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Seminare im Jahr 2019

Dark Matter Direct Detection Theory - From Extensions of the Standard Model to Observables
Dozent/Speaker: Dr. Christopher Körber (RUB, TPII)
Termin/Date: Do. 14.05.2020, 16:15 - 17:45
Ort/Location: virtual
Übersicht/Abstract: What is the nature of so called Dark Matter and does it interact with regular matter except through gravity? Direct detection experiments aim to answer this question. Yet, propagating measurements (or constraints) to the fundamental theory requires bridging several scales - from target nucleus to individual nucleons to the level of quarks & gluons and beyond. In this talk I describe the methods used, assumptions made and challenges faced by the bridging of scales to address implications of measurements.
Spinning black holes with Skyrme hairs and soliton stars
Dozent/Speaker: Dr. Yakov Shnir (JINR, Dubna, Russian Federation)
Termin/Date: Do. 12.03.2020, 15:00 - 16:30
Ort/Location: NB 6/173
Übersicht/Abstract: We study a new families of stationary rotating axially symmetric hairy black holes which represent solutions of the Einstein-Skyrme model in the Kerr spacetime. We found that the spinning axially symmetric cloudy solutions of the model also exist in the regular asymptotically flat space-time without the event horizon. The latter congurations are similar to the usual rotating boson stars, which, in the at flat space limit are linked to the axially symmetric Q-balls, in both cases the solutions exist for some restricted range of values of the angular frequency and possess a quantized angular momentum. Considering similar solution in the O(3) sigma model, we show that, depending on the values of the parameters of the model and the Hawking temperature, the branch structure of the corresponding cloudy solutions varies from the usual inspirraling pattern, which is typical for the boson stars, to the two branch structure, similar to that of the black holes with Skyrme hairs. As another examples of spinning black holes with synchronized hairs we consider families of parity-odd solutions of the Einstein-Klein-Gordon model. Finally, we discuss Dirac stars and compare their properties with the usual boson stars.
Calculation of The Three-Pion Exchange Nucleon-Nucleon Potential in Chiral Effective Field Theory
Dozent/Speaker: Victor Springer (RUB)
Termin/Date: Do. 27.02.2020, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Chiral effective field theory is a powerful tool in order to describe low energy nucleon-nucleon (NN) reactions. In this framework, a long range part of an NN potential is described by the exchange of pions. Whereas one and two pion exchanges were studied well in the past, only a few calculations to the three pion exchange exit in literature. Since in one of them singularities in the spectral function representation were found, it is of interest to study this potential in another way. In this talk, I will discuss the three pion exchange NN potential in a chiral EFT with the method of unitary transformation. Using dimensional regularization, the occurring two-loop tensor integrals are reduced to two so-called sunset master integrals. For those, a one-dimensional integral representation in terms of Bessel functions was found.
Novel chiral Hamiltonian and observables in light and medium-mass nuclei
Dozent/Speaker: Dr. Vittorio Somã, CEA Saclay, France
Termin/Date: Do. 30.01.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Recent advances in nuclear structure theory have led to the availability of several complementary ab initio many-body techniques applicable to light and medium-mass nuclei as well as nuclear matter. After successful benchmarks between different approaches, the focus is moving to the development of improved models of nuclear Hamiltonians, currently representing the largest source of uncertainty in ab initio calculations of nuclear systems. In this context, a novel parameterisation of a Hamiltonian based on chiral effective field theory has been recently introduced. Specifically, three-nucleon operators at next-to-next-to-leading order are combined with an existing (and successful) two-body interaction containing terms up to next-to-next-to-next-to-leading order. The resulting potential is labelled NN+3N(lnl). Using results from no-core shell model and self-consistent Green's function approaches, in this seminar I will explore the performance of this new interaction across light and medium-mass nuclei. Both systematics along complete isotopic chains and specific medium-mass isotopes of high experimental relevance will be discussed. Finally, perspectives on the description of doubly open-shell nuclei will be addressed.
Eigenvector Continuation as a Tool for Ab Initio Simulations
Dozent/Speaker: Dr. Dillon Frame (Forschungszentrum Jülich)
Termin/Date: Do. 28.11.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Eigenvector Continuation is a new mathematical tool that has been developed for use in determining the eigenvectors of Hamiltonian matrices in situations where obtaining them directly is otherwise impractical. This method relies on projecting the Hamiltonian into a low-dimensional subspace formed out of known eigenvectors, and using analytic continuation to determine the eigenvector of interest. In this talk, I will show the applications of this method to three systems: the Bose-Hubbard model, neutron matter on the lattice, and the non-perturbative inclusion of the Coulomb interaction in C-12 and O-16.
Study of Axial Pion Production in Chiral Perturbation Theory
Dozent/Speaker: Tim Höhne (University of Bochum)
Termin/Date: Do. 26.09.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In the present work we study axial pion production within heavy-baryon chiral perturbation theory. We set up the necessary theoretical framework and give the chiral Lagrangians describing the interactions among pions, nucleons and external sources. Afterwards we employ these Lagrangians to calculate the full axial pion production amplitude up to NNLO including tree- and loop contributions and renormalize it. For the comparison to experiments we then focus on weak charged current neutrino induced pion production containing axial pion production as a subprocess. This process does not only involve axial but also vector pion production. After also calculating and renormalizing the vector pion production amplitude up to NNLO, both amplitudes are combined and used to calculate the neutrino induced pion production total cross section. Plenty of consistency checks are deployed to assure the calculation was done correctly. Finally the obtained cross sections are compared to a covariant calculation as well as existing experimental data.
Lattice simulations with chiral effective field theory for light and medium-mass nuclei
Dozent/Speaker: Prof. Dr. Serdar Elhatisari (Karamanoglu Mehmetbey University, Karaman, Turkey)
Termin/Date: Do. 11.07.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Chiral effective field theory ($\chi$EFT) is a model-independent and systematic approach for describing the interactions between nucleons having energies below the chiral symmetry breaking scale. Nuclear lattice effective field theory (NLEFT) is a powerful numerical method formulated in the framework of $\chi$EFT to study the few- and many-nucleon problems. There has been significant progress in \emph{ab initio} nuclear structure and nuclear scattering calculations using NLEFT. In this talk I discuss recent developments in NLEFT calculations including degrees of locality of the nuclear forces, a new lattice formulation of $\chi$EFT interactions with a simpler decomposition into spin channels, Galilean invarience restoration interaction on the lattice etc. I also present recent results on the ground state energies of light and medium-mass nuclei from lattice simulations with $\chi$EFT at next-to-next-to-next-to-leading order.
Studies of 3-D Structure of the Nucleon from CLAS and CLAS12 at Jefferson Lab
Dozent/Speaker: Prof. Dr. Kyungseon Joo (University of Connecticut)
Termin/Date: Mi. 10.07.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Recent developments of generalized parton distributions (GPDs) and transversely dependent momentum distributions (TMDs) have opened a new window on a 3D imaging of the nucleon, going far beyond the one-dimensional, longitudinal structure probed in inclusive deep-inelastic scattering, and the transverse structure encoded in the different form factors. The 3D imaging of the valence quarks is a cornerstone of the new 12 GeV experimental program at Jefferson Lab, and a future proposed US-based electron ion collider (EIC) will extend this imaging to sea quarks and gluons. In this talk, I will describe recent measurements in exclusive and semi-inclusive deep processes with the CLAS detector, the CEBAF Large Acceptance Spectrometer at Jefferson Lab to study 3D structure of the nucleon, and I will also explore future directions using the new CLAS12 detector.
Symmetries, Ergodicity, and the Sign problem
Dozent/Speaker: Prof. Dr. Tom Luu (FZ Jülich)
Termin/Date: Do. 23.05.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The hybrid monte carlo algorithm (HMC) is a numerical workhorse in simulations of strongly interacting phenomena, such as lattice QCD, nuclear lattice EFT, and strongly correlated electrons in low dimensions. An implicit assumption in these HMC simulations is that the algorithm is ergodic, i.e. any state space can be reached with positive probability. However, this is not always the case and depends on the underlying symmetries of the system. HMC also requires a positive definite probability measure, a lack of which is known as the sign problem. These two aspects are not independent of each, and I show how attempts to solve one aspect may worsen the other. In particular, I describe how attempts to alleviate the sign problem via holomorphic flow leads to an ergodicity problem. I present solutions to such ergodicity issues via the use of `ergodicity jumps'. The interplay between ergodicity and the sign problem has direct bearing on lattice QCD simulations at finite baryon chemical potential and nuclear lattice EFT calculations of neutron-rich nuclei.
Few-body bound states and resonances in finite volume
Dozent/Speaker: Dr. Sebastian König (TU Darmstadt)
Termin/Date: Do. 16.05.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Since the pioneering work of Lüscher in the 1980s it is well known that considering quantum systems in finite volume, specifically, finite periodic boxes, can be used as a powerful computational tool to extract physical observables. While this formalism has been worked out in great detail in the two-body sector, much effort is currently being invested into deriving analogous relations for systems with more constituents. Such work is relevant not only for nuclear physics, where lattice methods are now able to calculate few- and many-nucleon states, but also for other fields such as simulations of cold atomic systems. In this talk, I will present recent progress that has been achieved for the extraction of few-body bound-state and resonances properties from finite-volume simulations, focusing on results that are valid for systems with an arbitrary number of constituents.
Three-particle dynamics and resonances in a finite volume
Dozent/Speaker: Prof. Dr. Hans-Werner Hammer (TU Darmstadt)
Termin/Date: Do. 9.05.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The three-particle quantization condition relates finite-volume energies obtained on the lattice to infinite-volume scattering amplitudes. It can be partially diagonalized in the center-of-mass frame by using the cubic symmetry on the lattice. Instead of spherical harmonics, the amplitudes are expanded in the basis functions of different irreducible representations of the octahedral group. We discuss the numerical solution and properties of such a projected quantization condition in a simple model and discuss their interpretation in terms of bound and scattering states.
Moreover, we discuss the extraction of multi-body resonance properties from avoided level crossings in finite volume spectra.
Exact summation of chiral logs in 2D: quasi-renormalizable QFTs, Dixon's elliptic functions, and all that
Dozent/Speaker: Dr. Kirill Semenov-Tian-Shansky (Petersburg Nuclear Physics Institute)
Termin/Date: Do. 18.04.2019, 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: We discuss the non-linear recurrence relations for the coefficients of Leading Logarithms (LLs) in massless Effective Field Theories (EFTs). These relations can be worked out relying on the fundamental properties of quantum field theory amplitudes: analyticity, unitarity and crossing symmetry and generalize the renormalization group technique for the case of non-renormalizable EFTs. We put particular emphasize on the 2D case and address the mathematical properties of the relevant class of non-linear recurrence relations. We present a number of highly non-trivial solutions in terms of elliptic functions. We introduce the class of quasi-renormalizable quantum field theories for which the summation of leading logarithmic corrections for $2 \rightarrow 2$ scattering amplitudes results in manifestation of an infinite number of the Landau poles. Finally, we present explicit examples of quasi-renormalizable QFTs in 2D.
Exclusive decays $\chi_{cJ}\rightarrow K^*(892)K $ within the effective field theory framework
Dozent/Speaker: Dr. Nikolay Kivel (Petersburg Nuclear Physics Institute)
Termin/Date: Do. 17.04.2019, 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: Charmonia hadronic decays $\chi_{cJ}\rightarrow K^*(892)\bar{K} $ are considered within the effective field theory framework. The colour-singlet and colour-octet contributions are studied using potential NRQCD effective theory. It is shown that the heavy quark spin symmetry allows one to establish the relation between the colour-octet matrix elements and to compute the hard spin symmetry breaking corrections. The obtained results are used for the phenomenological description of the measured branching fractions.
Weak reactions of the deuteron in $\chi$EFT
Dozent/Speaker: Dr. Bijaya Acharya (Uni Mainz)
Termin/Date: Do. 24.01.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Chiral effective field theory ($\chi$EFT) provides a unified framework for constructing nuclear potentials as well as the couplings of nuclei to external electroweak sources with controlled uncertainties. However, quantification of these uncertainties even for the simplest of nuclear systems present several challenges. I will present the results of the latest $\chi$EFT calculations, along with uncertainty estimates, for several electroweak observables involving the deuteron: (i) the proton-proton fusion reaction which can not be measured reliably in the lab, but is an important ingredient in stellar astrophysics models, (ii) the muon-deuteron capture rate whose upcoming measurement will determine the low energy constant $c_D$ that parametrizes the pion-range part of the three-nucleon force, and (iii) the response functions that enter the neutrino-deuteron scattering cross section, which upon extension to the medium-mass region of the nuclear chart, will provide important input for current and future neutrino experiments.
Relativistic ab initio calculation in finite nuclear systems and its promotion to nuclear density functional
Dozent/Speaker: Dr. Shihang Shen (University of Milan)
Termin/Date: Do. 17.01.2019, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Nuclear ab initio calculation is one of the most fundamental tasks of nuclear physics, and there have been many exciting progresses in the past. Yet it is still difficult to describe the whole nuclear chart using ab initio methods with a low-enough cost to achieve high-enough precisions, comparing with nuclear density functional theory. On the other hand, nuclear density functional has its difficulty and certain terms in the functional are difficult to be determined. In this case, ab initio calculation is important and can help to provide valuable information. I will discuss recent progress of one of the ab initio methods, the relativistic Brueckner-Hartree-Fock theory, in finite nuclear system, with emphasis on the importance of relativistic effect. Then I will show how such ab initio calculation can help to build better nuclear density functionals.

Seminare im Jahr 2018

Effective field theory and the derivation of the Salam-Weinberg model
Dozent/Speaker: Dr. Jambul Gegelia (FZ-Juelich)
Termin/Date: Do. 25.10.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We revisit the problem of deriving local gauge invariance with spontaneous symmetry breaking in the context of an effective field theory. We consider the most general Lagrangian of massive vector bosons interacting with a massive scalar field and massless U(1) gauge field. We impose the conditions of generating the right number of constraints for systems with spin-one particles and perturbative renormalizability as well as the separation of scales at one-loop order. We find that the above conditions result in severe restrictions on the coupling constants of the interaction terms. These restrictions lead to the gauge-invariant Lagrangian with spontaneous symmetry breaking taken in the unitary gauge as the leading order approximation to an effective field theory.
Bayesian Uncertainty Quantification for NN scattering
Dozent/Speaker: Prof. Dr. Daniel Phillips (Ohio University, USA)
Termin/Date: Do. 18.10.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk I will discuss two related aspects of our recent efforts to quantify the uncertainties in NN scattering calculations in chiral effective field theory (ChiEFT). First, I will show how truncation errors in effective field theories can be given a proper statistical interpretation using Bayesian methods. And I will then employ that statistical interpretation to infer the breakdown scale of the chiral EFT treatment of NN scattering from the convergence pattern of the ChiEFT series. But I will also explain why a full treatment of ChiEFT truncation errors in NN observables requires a model for the way in which those errors are correlated in scattering energy and angle. We have used Gaussian-process models for these correlations; I will describe those models and how their adoption affects the conclusions of our analyses of ChiEFT truncation errors. I will then turn my attention to parameter estimation in NN scattering, demonstrating how the use of posterior probability distributions for the ChiEFT low-energy constants that affect NN scattering can elucidate physics. I will finish by combining the two themes of my presentation, showing how the inclusion of truncation errors in parameter estimation yields confidence intervals for NN low-energy constants which do not depend on the energy range of the data included in the fit.
Adiabatic Hamiltonians: from Lattice Simulations to Continuum
Dozent/Speaker: Lukas Bovermann (RUB)
Termin/Date: Mi. 17.10.2018, 11:15 - 12:45
Ort/Location: NB 6/173
4-Nucleon-Force Contributions to $\alpha$-Binding Energy
Dozent/Speaker: Patrick Lipka, RUB, TP2
Termin/Date: Do. 11.10.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Abstract will follow later
Electromagnetic Nuclear Response Functions
Dozent/Speaker: Prof. Sonia Bacca (University Mainz)
Termin/Date: Do. 05.07.2018, 13:30 - 15:00
Ort/Location: NB 7/173
Übersicht/Abstract: Atomic nuclei drive the synthesis of chemical elements, serve as star fuel and as laboratories to test fundamental interactions and the Standard Model.¬† Predictions of nuclear properties that start from forces among nucleons and their interactions with external probes as described by chiral effective field theory are arguably the doorway to a solid connection between observations and the underlying fundamental theory of quantum chromo-dynamics.
Today, thanks to advances in many-body theory and high performance computing, we can calculate nuclear properties for increasingly large systems and estimate theoretical uncertainties. Nuclear response functions are key observables to study the nuclear dynamics. As such they have been subject of intensive studies. I will present recent highlights, that portrait the role of electromagnetic responses in tackling contemporary issues, such as the proton-radius puzzle and the neutron-skin thickness.
Dozent/Speaker: Prof. Peter Schweizer (University of Connecticut)
Termin/Date: Mi. 04.07.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Abstract will follow later
Search for possible light-quark exotics: Review of experimental data and interpretations.
Dozent/Speaker: Prof. V. Kuznetsov (Petersburg Nuclear Physics Institute)
Termin/Date: Mi. 27.06.2018, 13:15 - 14:45
Ort/Location: NB 7/173
Übersicht/Abstract: The decisive identification of a narrow enhancement at W ˜ 1.68 GeV in the excitation functions of the γn -> ηn (the so-called "neutron anomaly") and some other reactions is one of the challenges in the domain of hadronic physics. Furthermore the recent experimental data reveal two resonant structures at W ˜ 1.68 GeV and W ˜ 1.72 GeV.
These structures may signal the existence of one (N(1685)) or two narrow resonances (N(1685) and N(1726)). The properties of N(1685), if it does really exist, namely the strong photo-excitation on the neutron and the suppressed decay to the πN final state, do coincide well to those expected for the second member of the exotic anti-decuplet predicted in the framework of the Chiral Soliton Model.
The review of recent experimental data and their interpretations will be presented. It seems questionable if the interference phenomena suggested by Bonn-Gatchina and several other group- sciteani, could explain the whole complex of experimental findings. More probable hypotheses would be either the existence of one or two narrow resonances N(1685) and N(1726) or the sub-threshold virtual meson-nucleon production (cusps).
Dozent/Speaker: Prof. Dr. Michal Praszalowicz (Jagiellonian University, Krakow)
Termin/Date: Fr. 27.04.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Recent measurements of the total pp cross-section and the so called rho parameter by the TOTEM Collaboration at the LHC cannot be reconciled with the parametrizations of the forward scattering amplitude that does not include a C-parity odd contribution, so called odderon. We shall¬† review the S matrix approach to the low momentum transfer processes introducing the concepts of Regge trajectories, Pomeron and odderon. QCD interpretation of the Pomeron and the odderon will be discussed. Finally we shall present recent analysis of the TOTEM data that seem to indicate the evidence for the odderon.
Will be announced soon
Dozent/Speaker: Prof. Dr. A.L. Kataev (INR RAS, Moscow)
Termin/Date: Do. 26.04.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Scheme and gauge (in)dependence of the ¬†generalized Crewther relation between e^+e^- - annihilation Adler function and polarised Bjorken sum rule in perturbative QCD and the $\]beta$-function factorization property
On a possibility of baryonic exotica
Dozent/Speaker: Prof. Dr. Michal Praszalowicz (Jagiellonian University, Krakow)
Termin/Date: Do. 19.04.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Models based on chiral symmetry predict the baryonic states with exotic quantum numbers (pentaquarks) that have relatively low masses and small widths. We shall briefly review both theoretical and experimental status of a possibility of exotica in the light sector. Next we shall show how to extend chiral models to baryons with one heavy quark and show that one may expect exotic states also in this case. Finally we shall try to interpret recently discovered by the LHCb collaboration five Omega^*_c resonances in terms of regular and exotic excitations of the ground state Omega_c.
Neutrinoless double beta decay in effective field theory
Dozent/Speaker: Dr. Jordy de Vries (NIKHEF, Amsterdam)
Termin/Date: Di. 13.02.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Next-generation neutrinoless double-beta decay experiments aim to discover lepton-number violation in order to shed light on the nature of neutrino masses. A non-zero signal would have profound implications by demonstrating the existence of elementary Majorana particles and possibly pointing towards a solution of matter-antimatter asymmetry in the universe. However, the interpretation of the experimental signal (or lack thereof) requires care. First of all, a single nonzero measurement would indicate lepton-number violation but will not identify the underlying source. Second, complicated hadronic and nuclear input is required to connect the experimental data to a fundamental description of lepton-number violation. In this talk, I will use effective field theories to describe neutrinoless double-beta decay processes. In particular, I will apply the Standard Model effective field theory and chiral effective field theory to bridge the gap between high-energy models of lepton-number violation to neutrinoless double-beta decay experiments.
Few-neutron resonance study using transition operators
Dozent/Speaker: Dr. Arnoldas Deltuva (Vilnius University)
Termin/Date: Do. 01.02.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Existing bound-state type calculations of few-neutron resonances yield contradicting results. A direct study of the three- and four-neutron continuum using rigorous scattering equations with realistic potentials and search for possible resonances is aimed. Faddeev-type integral equations for transition operators are solved in the momentum-space partial-wave framework. The evolution of resonances is studied by enhancing the strength of the two-neutron interaction in partial waves with nonzero orbital momentum. Calculated few-neutron transition operators exhibit resonant behavior for sufficiently large enhancement factors; pole trajectories in the complex-energy energy plane are extracted from their energy dependence. However, the resonant behavior completely disappears for the physical interaction strength.
Production of tensor glueball in reaction $\gamma\gamma\rightarrow G_2\pi^0$
Dozent/Speaker: Dr. N. Kivel (Universität Mainz)
Termin/Date: Do. 11.01.2018, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We studied production of tensor glueball in the reaction $\gamma\gamma\rightarrow G_2\pi^0$ at large energy and large scattering angles.
The scattering amplitude is computed within the collinear factorisation framework that allows us to estimate the cross section. We obtained that if the value of the tensor gluon coupling is not too small $f^T_g\sim 100$~MeV then the cross section can be measured in the future BELLE-II experiment.

Seminare im Jahr 2017

Three-body scattering in isobar formulation
Dozent/Speaker: Dr. Maxim Mai (George Washington University)
Termin/Date: Do. 02.11.2017, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In the so-called isobar parametrization the three-particle states are populated via an interacting two-particle system (resonant or non-resonant), and a spectator. Using this parametrization, we derive the isobar-spectator interaction such that the three-body Unitarity is ensured exactly. In the first part of my talk I will show the major steps of this derivation. (arXiv:1706.06118)
The second part of the talk will be dedicated to the finite-volume implementation of the framework (arXiv:1709.08222). Imaginary parts in the infinite volume, dictated by Unitarity, determine the dominant power-law finite volume effects to ensure the correct 3-body quantization condition. Furthermore, various building blocks of the 3->3 amplitude in the finite volume can become singular. However, when all contributions are summed-up, only genuine 3-body singularities remain. I will demonstrate the corresponding cancellation mechanisms explicitly for the simplified case of only one S-wave isobar.
Current Conservation in Effective Field Theories for the Two-Nucleon System
Dozent/Speaker: Daniel Möller
Termin/Date: Do. 14.09.2017 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: It is well understood that the two-nucleon system in chiral effective field theory can be treated non-perturbatively solving a suitably regularized Lippmann-Schwinger equation. However, it is not evident yet how to properly regularize and include in this framework electromagnetic current operators. On these grounds the renormalization of electromagnetic interaction in the two-nucleon system at very low energies is studied. Since the interest is in the regime well below the pion production threshold, the approach proposed here is based on two-nucleon contact interactions only. In this case the two-nucleon potential is separable and the Lippmann-Schwinger equation is solvable analytically. The regularized current is consistently derived from the regularized potential via current conservation and the functionality of this scheme is verified by the comparison of the results to those within the perturbative treatment by Kaplan, Savage, and Wise, where renormalization is transparent. Observables are computed for both cases and it is shown that consistent current regularization is needed to produce reliable results.
Nucleon Mass in Chiral Pertubation Theory Beyond one Loop
Dozent/Speaker: Nils Conrad
Termin/Date: Di. 12.09.2017 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The nucleon mass is calculated in SU(2) chiral perturbation theory up to the chiral order O(q^6). For that purpose a power counting scheme is constructed and all self energy diagrams up to order O(q^6) are taken into account, which include two loop diagrams. The diagrams are reduced to a small set of master integrals using an algorithm from Tarasov (1997). A further goal is to renormalize the remaining integrals using extended-on-the-mass-shell renormalization, so that the renormalized expressions are consistent with the power counting.
Extracting scattering observables and resonance properties from lattice QCD
Dozent/Speaker: Dr. Maxwell T Hansen (Mainz University)
Termin/Date: Do. 20.07.2017 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: QCD, the quantum theory of the strong force, gives rise to a rich variety of short-lived resonance states. Understanding these in detail is of great interest, both for predicting backgrounds in new-physics searches and for gaining general insight into strong-force dynamics and phenomenology. The numerical technique of lattice QCD (LQCD), which has proven very successful in studying the properties stable hadrons, should also play an important role in understanding states that decay via the strong force. However, numerical LQCD calculations are necessarily performed in a finite volume and with Euclidean time, and this limits the extraction of the scattering and transition amplitudes required for characterizing resonant states. In the past decades, great progress has been made to overcome this limitation by using finite volume as a tool rather than an artifact, and deriving non-perturbative, analytic relations between the finite- and infinite-volume theories. I will review recent developments in this work with particular focus on three-hadron final states.
Bringing Light into the Darkness? About Dark Matter Scattering off Light Nuclei
Dozent/Speaker: Dr. Christopher Körber (Forschungszentrum Jülich)
Termin/Date: Do. 13.07.2017, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: What do we know about Dark Matter and how can we possibly describe it on a fundamental scale?
In this talk, I present the scattering of Dark Matter particles off various light nuclei within the framework of chiral effective field theory. I focus on scalar interactions and include one- and two-nucleon scattering processes whose form and strength are dictated by chiral symmetry. The nuclear wave functions are calculated from chiral effective field theory interactions as well. The convergence pattern of the chiral expansion in the nuclear potential and the Dark Matter-nucleus currents is investigated. This allows to provide a systematic uncertainty estimate of the calculations. Results for ${}^2$H, ${}^3$H, and ${}^3$He nuclei, which are theoretically interesting and the latter is a potential target for experiments, are provided.
The Nucleon Axial Charge from QCD
Dozent/Speaker: Dr. Evan Berkowitz (Forschungszentrum Jülich)
Termin/Date: Do. 29.06.2017, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The axial charge g_A=1.2723(23) is one of the essential characterizations of the nucleon and plays a fundamental role in our understanding of nuclear physics, controlling nuclear beta decay and pion exchange. It has long been considered a critical benchmark for lattice QCD and yet has proved substantially more challenging to compute than expected. I will describe our recent calculation [ largely described in ], g_A = 1.283(17) and explain the new analytic results and associated computational strategies that, when combined with improved algorithms and leadership-class computing, have unlocked this and other nuclear matrix elements.
On a possibility of charmed exotica
Dozent/Speaker: Prof. Hyun-Chul Kim (Inha University, Incheon, Republic of Korea)
Termin/Date: Do. 01.06.2017, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We employ the chiral quark-soliton model to describe excited baryons with one heavy quark. Identifying known charmed baryons with multiplets allowed by the model, we argue that apart from regular excitations of the ground state multiplets, some of recently reported by the LHCb collaboration narrow Omega_c states, may correspond to the exotic pentaquarks. This interpretation can be easily verified experimentally, since exotic Omega_c†states -- contrary to the regular excitations -- form isospin triplets, rather than singlets.
Self-dual solitons in the Skyrme model
Dozent/Speaker: Dr. Yakov Shnir (JINR, Dubna, Russia)
Termin/Date: Do. 18.05.2017, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We discuss recent development, related with construction of self-dual soliton solutions of the generalized Skyrme model. A new model is proposed, which possesses a self-dual sector that saturates the Bogomolny bound leading to an energy depending linearly on the topological charge. The self-duality equations are conformally invariant in three space dimensions leading to a toroidal ansatz and exact self-dual Skyrmion solutions. Those solutions are labelled by two integers and, despite their toroidal character, the energy density is spherically symmetric when those integers are equal and oblate or prolate otherwise.
Soft-/rapidity- anomalous dimension correspondence
Dozent/Speaker: Dr. Alexey Vladimirov (Regensburg University)
Termin/Date: Do. 20.12.2016, 10:15 - 11:45
Ort/Location: NB 6/173
Übersicht/Abstract: We present the overview of the modern factorization theorems with the emphasis on the structure of soft factors. In particular, we discuss recently discovered correspondence between soft factors for multi-particle production and for multi-parton scattering. The correspondence is valid to all orders of perturbation theory and provides a proof of rapidity renormalization procedure for multi-parton scattering soft factors (including the transverse momentum dependent (TMD) soft factor as a special case). It also results to an exact relation between the rapidity anomalous dimension and the well-known soft anomalous dimension. The three-loop rapidity anomalous dimensions for TMD and a general multi-parton scattering are derived.
Relativistic nucleon-nucleon interaction in chiral effective field theor
Dozent/Speaker: Dr. Xiu-Lei Ren (RUB, Bochum, Deutschland)
Termin/Date: Do. 15.12.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the strong need for a covarian chiral force in relativistic nuclear structure studies, we develop a new covariant scheme to construct the nucleon-nucleon interaction in th framework of chiral effective field theory. In this talk, I will highlight the relativistic effects of chiral nuclear force up to leadin order, which can improve the description of the scattering phase shifts with low angular momenta than the leading order Weinberg approach Particularly, the description of the 1S0, 3P0, and 1P1 partial waves is similar to that of the next-to-leading order Weinberg approach. Thi covariant formulation appears to be more efficient than the non-relativistic one and may provide an essential input to relativistic nuclea structure studies

Seminare im Jahr 2016

Soft-/rapidity- anomalous dimension correspondence
Dozent/Speaker: Dr. Alexey Vladimirov (Regensburg University)
Termin/Date: Do. 20.12.2016, 10:15 - 11:45
Ort/Location: NB 6/173
Übersicht/Abstract: We present the overview of the modern factorization theorems with the emphasis on the structure of soft factors. In particular, we discuss recently discovered correspondence between soft factors for multi-particle production and for multi-parton scattering. The correspondence is valid to all orders of perturbation theory and provides a proof of rapidity renormalization procedure for multi-parton scattering soft factors (including the transverse momentum dependent (TMD) soft factor as a special case). It also results to an exact relation between the rapidity anomalous dimension and the well-known soft anomalous dimension. The three-loop rapidity anomalous dimensions for TMD and a general multi-parton scattering are derived.
Relativistic nucleon-nucleon interaction in chiral effective field theor
Dozent/Speaker: Dr. Xiu-Lei Ren (RUB, Bochum, Deutschland)
Termin/Date: Do. 15.12.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the strong need for a covarian chiral force in relativistic nuclear structure studies, we develop a new covariant scheme to construct the nucleon-nucleon interaction in th framework of chiral effective field theory. In this talk, I will highlight the relativistic effects of chiral nuclear force up to leadin order, which can improve the description of the scattering phase shifts with low angular momenta than the leading order Weinberg approach Particularly, the description of the 1S0, 3P0, and 1P1 partial waves is similar to that of the next-to-leading order Weinberg approach. Thi covariant formulation appears to be more efficient than the non-relativistic one and may provide an essential input to relativistic nuclea structure studies
Hard electroproduction of tensor mesons within the QCD factorization framework
Dozent/Speaker: Dr. Nikolai Kivel (Universität Mainz)
Termin/Date: Do. 01.12.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Due to multiple possible polarizations hard exclusive production of tensor mesons by virtual photons or in heavy meson decays offers interesting possibilities to study the helicity structure of the underlying short-distance process. Motivated by the first measurement of the transition form factor Y^* -> Y F^2(1270) at large momentum transfers by the BELLE collaboration we present an improved QCD analysis of this reaction in the framework of collinear factorization including contributions of twist-three quark-antiquark- gluon operators and an estimate of soft end-point corrections using light-cone sum rules. The results appear to be in good agreement with the data, in particular the predicted scaling behavior is reproduced in all cases.
The quark model and the missing hyperons
Dozent/Speaker: Prof. Dr. Fred Myhrer
(USC, South Carolina, USA)
Termin/Date: Do. 07.07.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The seminar will discuss the first excited Lambda og Sigma states. Different quark model evaluations will be presented. The different evaluated configuration mixing will influence the hyperon decay branching ratios, which can be measured.
The energy-momentum tensor of the nucleon, and the new charmonium-pentaquark states at LHCb
Dozent/Speaker: Prof. Dr. P. Schweitzer
(UConn, Conneticut, USA)
Termin/Date: Do. 30.06.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Information on the nucleon form factors of the energy-momentum tensor (EMT) can, in principle, be accessed via generalized parton distribution functions from studies of hard-exclusive reactions. This promises new insights like the spin decomposition of the nucleon, or mechanical nucleon properties related to the stress tensor. The prospects to learn in this way new lessons about the nucleon have triggered in the recent past significant interest in generalized parton distribution functions and EMT form factors. Recently, it was shown that the knowledge of the EMT form factors has also a very practical application: it can be used to describe the effective interaction of charmonia with baryons, and provide an appealing explanation of the binding mechanism of the charmonium-pentaquark states observed last year at LHCb. In this talk, the physics content of the EMT form factors is discussed, the application to charmonium-pentaquarks is sketched, and recent progress is reviewed.
Recent Results in Nuclear Lattice Effective Field Theory
Dozent/Speaker: Prof. Dr. Dean J. Lee
(NCSU, North Carolina, USA)
Termin/Date: Do. 23.06.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: This talk reviews some recent progress made by the Nuclear Lattice Effective Field Theory Collaboration. In the first part I discuss an ab initio calculation of alpha-alpha scattering which uses a technique called the adiabatic projection method. In the second part I present evidence that nuclear matter is near a quantum phase transition. I discuss the control parameter for this transition and consequences for nuclear clustering and the binding of protons and neutrons within nuclei.
QCD evolution of sum rules and positivity constraints
Dozent/Speaker: Prof. Dr. Oleg Teryaev
(JINR, Dubna, Russland)
Termin/Date: Do. 13.06.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Stability of sum rules and positivity constraints for various parton distributions is naturally explained in the framework of kinetic interpretation of relevant QCD evolution equations. The latter imply the scale arrows being the full analogs of time arrow. The new twist-3 energy-momentum sum rule is considered and the related experimental studies of T-odd spin asymmetry in Drell-Yan process are discussed.
Nuclear physics from (lattice) quantum chromodynamics
Dozent/Speaker: Dr. Johannes Kirscher
(The Hebrew University of Jerusalem, Jerusalem, Israel)
Termin/Date: Do. 09.06.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will present recent progress in the fundamental derivation of the theory of nuclei. The lattice method to derive few-nucleon amplitudes directly from QCD will be introduced as an experimental apparatus. For the analysis of its data I will describe a theoretical framework with a brief motivation for the effective-field-theory formalism. Result obtained within this approach for the three and four-nucleon system and an outlook on the future of the program, which comprises the investigation of electromagnetic properties and the inclusion of additional degrees of freedom, will conclude the talk.
Lamb shift in light muonic atoms: constraints from photonuclear sum rules
Dozent/Speaker: Dr. Misha Gorshteyn
(Johannes Gutenberg-Universität Mainz, Mainz, Deutschland)
Termin/Date: Do. 28.04.2016, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I generalize the photonuclear sum rule of Levinger and Bethe to the case of virtual photons and show that the nuclear magnetic polarizability can be directly extracted from the inclusive electrodisintegration data. I consider the case of the deuteron and He-3 to study the validity of this new sum rule. I apply the new sum rule to the calculation of the nuclear polarizability correction to the Lamb shift in muonic deuterium and helium-3 in the context of the "proton radius puzzle" and the experiments on the muonic atoms spectroscopy where nuclear and hadronic structure-dependent corrections are amongst the main sources of the uncertainty for the extraction of nuclear radii.
Coupled-channel dynamics for charmonium-like states
Dozent/Speaker: Fabian Schefczik
(RUB, Bochum, Deutschland)
Termin/Date: Mi. 23.03.2016, 14:15 - 15:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk we address the interpretation of the X(3872) state found in the charmonium spectrum as a heavy-meson molecule consisting of a D and a D* meson. Using the framework of heavy hadron chiral perturbation theory (HHChPT) we derive the LO potentials for the interaction between the mesons, which, to this order, consist of the contact and the one-pion exchange potentials. Heavy quark spin symmetry suggests the existence of a molecular partner state of the X(3872) near the D*D* threshold. In order to investigate this issue, we derive partial wave coupled channel equations for the D*D* problem, whose solution allows us to find the D*D* partner state of the X(3872). In particular, we calculate the binding energy of the D*D* molecule up to second order corrections in the contact range theory. We investigate the role of non-perturbative static one-pion exchange and estimate the size of corrections from three body dynamic. The role of particle coupled channel effects is also discussed.
Confinement as spontaneous breakdown of translational invariance
Dozent/Speaker: Maxim Polyakov ((Petersburg Nuclear Physics Institute, St. Petersburg, Russia)
Termin/Date: Fr. 05.02.2016 , 10:00 - 11:30
Ort/Location: NB 7/173
Übersicht/Abstract: The traditional interpretation of heavy quark confinement in terms of Wilson area law was suggested more than forty years ago. From the very beginning it was clear that some sort of string picture must stand behind the area law. But it took time to rectify the theory, eliminating naive models and imprecise arguments (whatever important they could be historically), and to organize the chaos of various approximations to a systematic expansion in a single small expansion parameter (inverse size of the contour in case of Wilson loops). Nowadays we understand that the area law is just the top of an iceberg and that a much more fundamental phenomenon determines physics of confinement: "effective string formation". This phenomenon allows for a precise theoretical definition in terms of native matrix elements of the gauge theory without appealing to models, to fundamental string theory and without unnecessary assumptions like large Nc, SUSY or AdS/CFT framework. The phenomenon of "effective string formation" has many common features with spontaneous breakdown of continuous symmetries. In particular, one can construct effective Lagrangian containing all terms compatible with the pattern of spontaneously broken and non-broken symmetries and one can order these terms according to the gradient counting. This approach known as effective string theory (EST) is similar to EChPT. The spontaneously broken symmetry is translational invariance. The EST analog of Weinberg term is Nambu string action. In applications to Wilson loops the role of the small parameter justifying the applicability of EST is played by the inverse size of Wilson loop 1/L. A peculiar feature of EST is that NLO terms of EST contribute to Wilson loops starting from a rather high order of 1/L3. Therefore EST has a high-precision predictive power with only one parameter of the effective action (string tension). Predictions of EST were successfully tested on the lattice for various gauge groups and various space-time dimensions. Especially impressive tests of EST are done in D=3 Z2 gauge theory where combining Z2/Ising duality and advanced lattice algorithms one can achieve an unprecedented accuracy for very large Wilson loops in MC simulations.
Short-Distance RG-Analysis of X(3872) Radiative Decays"
Dozent/Speaker: Daniel A. S. Molnar (University of São Paulo, São Paulo, Brazil)
Termin/Date: Do. 04.02.2016 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Exotic mesons are states which do not fit in the conventional quark model. The exotic meson X(3872) is one of the first states to be observed experimentally, and consequently one of the most studied. Recently, possible explanations about its structural nature have been discussed in the literature. Among them, the molecular interpretation is one of the most successful, since X(3872) hadronic decays appear to be very well described by a molecular structure of two other loosely-bound mesons D and D* providing the dominant long-distance behavior. Nevertheless, radiative decays may have a relevant contribution from short-range physics. In this work, we perform a renormalization-group analysis to estimate the sensitivity of the X(3872) radiative decays regarding the long- and short-distance contributions.
LHCb pentaquarks
Dozent/Speaker: Maxim Polyakov (RUB, Bochum, Deutschland)
Termin/Date: Do. 28.01.2016 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We interpret the newly discovered pentaquark Pc(4450) as a bound state of charmonium ψ(2S) and the nucleon. The binding potential is due to charmonium-nucleon interaction that in the heavy quark approximation is proportional to the product of the charmonium chromoelectric polarizability and the nucleon energy-momentum distribution. We use the large Nc expansion to estimate the quarkonium polarizability and calculate the nucleon properties in the framework of the mean-field picture of light baryons. Two almost degenerate states JP=(1/2)- and JP=(3/2)- are predicted at the position of the Pc(4450) pentaquark. We find that the nucleon-ψ(2S) bound state has a naturally narrow width in the range of tens of MeV. The unitary multiplet partners of the Pc(4450) pentaquark and the generalization to bb-nucleon pentaquark bound states are discussed.
Light nuclei in a pionless effective field theory using the stochastic variational method
Dozent/Speaker: Dr. Vadim Lensky (Johannes-Gutenberg Universität, Mainz, Deutschland)
Termin/Date: Do. 14.01.2016 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We construct a potential model based on the low-momentum pionless effective field theory with a Gaussian regulator, and apply this to the nuclei with atomic number less than or equal to 4, using the stochastic variational method to solve for the nuclear wave functions. We look for consistency between the binding energies and the charge radii of these nuclei, and show that to next-to-next-to leading order the method shows excellent convergence, even for a system as dense as 4He.

Seminare im Jahr 2015

Four-nucleon reactions
Dozent/Speaker: Dr. Arnoldas Deltuva (Vilnius University, Vilnius, Lithuania)
Termin/Date: Do. 10.12.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Four-nucleon reaction calculations at energies above the four-body breakup threshold will be presented. They were performed in the momentum-space framework for transition operators. Results have been obtained for n+3H and p+3He elastic scattering and for elastic, charge-exchange, transfer, and breakup reactions initiated by n+3He, p+3H, or d+d collisions.
A description of χcJ → e+e- decay within the effective theory framework
Dozent/Speaker: Dr. Nikolai Kivel (Johannes Gutenberg-Universität, Mainz, Germany)
Termin/Date: Do. 03.12.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We present a calculation of the width for χcJ → e+e- decay. The amplitude of the process is computed within the NRQC framework. The leading-order contribution is described by two terms associated with the two different integration domains in the electromagnetic loop describing two-photon annihilation of the heavy quark-antiquark pair. The corresponding operators are defined in the framework of NRQCD. The matrix element of one of these operators describes a configuration with an ultrasoft photon. In order to compute this contribution we use the heavy hadron chiral perturbation theory. We obtain that this contribution is numerically dominant.
Magnetic monopoles: Neverending Story
Dozent/Speaker: Prof. Dr. Yakov Shnir (Oldenburg University)
Termin/Date: Do. 15.10.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In the history of theoretical physics the hypothesis about a possible existence of a magnetic monopole clearly has no analogy. There is no other purely theoretical construction which would manage not only survive without any experimental evidence in the course of more then a century, but remains in the focus of the intensive research of generations of physicists.
For the last 25 years the theory of magnetic monopole surprisely becomes closely connected with many actual directions of theoretical physics, like for example, the problem of confinement in Quantum Chromodynamics, the problem of proton decay, astrophysics and evolution of the early Universe, or supersymmetrical extension of the Standard Model, to name just a few. It looks plausibly that the answer on the question: "Why in our World a monopole does not exist?" is a key to the understanding of very foundations of Nature.
The talk will survey the developments of the monopole theory from 1269 to the present time. A brief discussion of the different aspects of the monopole, including current experimental status of the monopole, shall be presented.
Reduction Formalism of Two-Loop Integrals
Dozent/Speaker: Nora Rijneveen (RUB, Bochum, Deutschland)
Termin/Date: Do. 24.09.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Nowadays, high precision calculations in chiral perturbation theory require demanding calculations up to two-loop order. On this level it is much more efficient to automatize the calculations. As the first step towards this direction within chiral effective field theory we reconsidered the reduction formalism of two-loop self-energy integrals. This work shows how these integrals can be reduced to master integrals. The methods that are needed to obtain recurrence relations and to deal with tensor integrals are presented. Subsequently, the required reduction relations are derived systematically. The formalism is applied to the pion mass and an outlook is given.
The Reaction γN → γNπ in Chiral Perturbation Theory
Dozent/Speaker: Jan Hildebrand (RUB, Bochum, Deutschland)
Termin/Date: Di. 22.09.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We study reaction in γN → γNπ in the framework of Chiral Perturbation Theory up to the second order with Δ(1232) as an explicit degree of freedom. The results are compared with recent experimental data to γp → γpπ⁰ at MAMI and a Low Energy Constant has been fitted. On doing so, the effect of the Δ-resonance is of special interest.
Chiral-odd GPDs in multi-color limit of QCD
Dozent/Speaker: Prof. Dr. Peter Schweitzer (University of Connecticut, Connecticut, USA)
Termin/Date: Do. 30.07.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Generalized parton distribution functions (GPDs) are among the most fascinating and promising novel tools to learn new lessons about the quark-gluon structure of the nucleon. Not much is known from experiment about GPDs. This is in particular the case for chiral-odd GPDs, which only recently emerged as promising tools to describe certain subleading twist observables in hard-exclusive pion and eta-meson production in an effective handbag approach. In this talk the results are reported of a recent study of chiral-odd GPDs in the multi-color limit of QCD. While it is experimentally well-established that the number of colors in nature is Nc = 3, from theoretical point of view the formal expansion in powers of the 'small parameter' 1/Nc is a powerful first-principle approach. The obtained results explain trends seen in recent data from Jefferson Lab.
NN scattering in Lattice Effective Field Theory: Progress and perspectives
Dozent/Speaker: Dr. Jose Manuel Alarcon Soriano, Universität Bonn, HISKP
Termin/Date: Fr. 24.07.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk I will overview some recent important developments in the study of NN scattering within the Lattice Effective Field Theory (Lattice EFT) formulation. First, I will show briefly how the theory is formulated on the lattice, and how the observables are computed. Later, I will comment on the recent improvements made in the extraction of these observables, and study the convergence of the approach. Also, I will show the first attempt to study the lattice spacing dependence in the transfer matrix formalism, and show that a good description of the S-waves can be obtained at leading order for smaller spacings. Finally, I will comment on some techniques that recently appeared in the literature, and that could help in solving some problems persisting in the current formulation.
Physics Opportunities with a secondary K_L^0 Beam at JLab
Dozent/Speaker: Prof. Dr. Moskov Amaryan (Old Dominion University, Norfolk, USA)
Termin/Date: Do. 23.07.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk we discuss Letter of Intent submitted to JLab PAC to create secondary beam of K_L beam. It is shown that using high current electron beam of CEBAF an intensive beam of bremsstrahlung photons could be used to produce a K_L beam in the range of few hudred MeV up to (6-7) GeV to impinge on physics target of GLUEX experiment at Hall-D. Estimated intensity of the K_L beam on the order of 10^4/s is the highest ever achieved for the hadron spectroscopy. This will allow to observe dozens of predicted excited hyperon states that so far escaped being observed. A rich program with hydrogen and deuterium targets may be extended using polarized targets and draw an exciting avenue towards complete experiment with measurement of all underlying partial wave amplitudes of KN scattering.
Light front representation of transverse densities in the chiral periphery of the nucleon
Dozent/Speaker: Dr. Carlos Granados (Uppsala University, Uppsala, Sweden)
Termin/Date: Do. 25.06.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The pion contributions to the electric and magnetic transverse densities of the nucleon are studied for peripheral distances (~O(Mp-1)) where the dynamics are dominated by ChEFT and the densities can be calculated model-independently through ChPT. These densities are computed as overlap integrals of light front wave functions associated to the pion-nucleon (and Delta) fluctuations of the nucleon in light front time. This methodology allows the development of a first quantized description of a relativistic system from which important features of transverse densities are revealed. The orbital motion of the peripheral pion causes a large left-right asymmetry of the current in a transversely polarized nucleon, which results in the approximate equality of the peripheral charge and magnetization densities. The striking effect testifies to the essentially relativistic nature of chiral dynamics and could be observed in nucleon electromagnetic form factor measurements at low momentum transfer. The methodology developed here can be applied to nucleon form factors of other operators, such as the energy-momentum tensor.
Pion and rho-meson structure from Sum Rules
Dozent/Speaker: Dr. Alexander Pimikov (BLTP, JINR, Dubna, Russia)
Termin/Date: Do. 18.06.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The quark structures of the pion and the rho-meson are considered in different approaches using different types of Sum Rules: QCD Sum Rules with nonlocal condensates (NLC), Light Cone Sum Rules (LCSR), and Anomaly Sum Rules (ASR) to address form factors and distribution amplitudes. The LCSR approach was minutely studied in the low-momentum region, where different sources of theoretical uncertainties were estimated. The applicability limit of the LCSRs at low momenta is discussed by employing the comparison of results on the pion-photon transition form factor obtained in LCSR and Anomaly SR. Using QCD sum rules with NLCs, we show that the distribution amplitude of the longitudinally polarized rho-meson may have a shorttailed platykurtic profile in close analogy to our recently proposed platykurtic distribution amplitude for the pion. Such a chimera distribution de facto amalgamates the broad unimodal profile of the distribution amplitude, obtained with a Dyson-Schwinger equations-based computational scheme, with the suppressed tails characterizing the bimodal distribution amplitudes derived from QCD sum rules with nonlocal condensates.
How can we unravel the mysteries of the XYZ states
Dozent/Speaker: Prof. Dr. Christoph Hanhart (Forschungszentrum Jülich)
Termin/Date: Do. 28.05.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In recent years many states were discovered both in the charmonium as well as i the bottomonium sector that do not fit into the standard quark model picture - thi is especially true for the charged states $Z_b(10610)$, $Z_b(10650)$, $Z(4430)$ $Z_c(3900)$ and $Z_c(4020)$ The nature of these states is heavily discussed in the literature. The mos prominent proposals put forward are compact tetraquarks -- bound states o heavy diaquarks and heavy anti-diquarks --- hadroquarkonia --- a compac quarkonium core surrounded by a light quark cloud --- or hadronic molecules -- bound states of two color neutral mesons
Analytic Evolution of Singular Distribution Amplitudes in QCD
Dozent/Speaker: Dr. A. Tandogan-Kunkel (Forschungszentrum Jülich)
Termin/Date: Do. 21.05.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We describe a method of analytic evolution of distribution amplitudes (DA) that have singularities, such as non-zero values at the end-points of the support region, jumps at some points inside the support region and cusps. We illustrate the method by applying it to the evolution of a flat (constant) DA, antisymmetric flat DA and then use it for evolution of the two-photon generalized distribution amplitude. Our approach has advantages over the standard method of expansion in Gegenbauer polynomials, which requires infinite number of terms in order to accurately reproduce functions in the vicinity of singular points, and over a straightforward iteration of an initial distribution with evolution kernel. The latter produces logarithmically divergent terms at each iteration, while in our method the logarithmic singularities are summed from the start, which immediately produces a continuous curve, with only one or two iterations needed afterwards in order to get rather precise results.
A recipe for EFT uncertainty quantification
Dozent/Speaker: Prof. Dr. Richard J. Furnstahl (Ohio State University, USA)
Termin/Date: Do. 30.04.2015 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: As theoretical calculations of nuclear structure and reactions become more precise, there is increasing awareness of the need for better uncertainty quantification (UQ). Theory errors are usually systematic rather than random. Examples are the errors from using a finite harmonic oscillator basis and the errors from omitted higher-order terms in an effective field theory (EFT) expansion. I will focus on UQ in nuclear EFT calculations and illustrate how a Bayesian framework can be used to avoid overfitting of EFT constants, assess and propagate EFT truncation errors, and diagnose whether the EFT is working as advertised.
Antinucleon-Nucleon Interaction and the Related Hadron Physics
Dozent/Speaker: Dr. Xian-Wei Kang (FZ Jülich)
Termin/Date: Do. 12.03.2015 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: See abstract for further details
Bochum-Cracow collaboration on three-nucleon reactions: achievements and challenges
Dozent/Speaker: Prof. Dr. Henryk Witala
Jagiellonian University, Cracow, Poland
Termin/Date: Do. 23.04.2015 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Zeilen der Zusammenfassung / der Übersicht über den Vortrag
A new approach to piecewise linear Wilson lines
Dozent/Speaker: Dr. Frederik van der Veken
University of Antwerp, Department of Physics, Belgium
Termin/Date: Do. 05.02.2015, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Wilson lines are key objects in many QCD calculations. They are parallel transporters of the gauge field that can be used to render non-local operator products gauge invariant, which is especially useful for calculations concerning validation of factorisation schemes and in calculations for constructing or modelling parton density functions. We develop an algorithm to express Wilson lines that are defined on piecewise linear paths in function of their Wilson segments, reducing the number of diagrams needed to be calculated. We show how different linear path topologies can be related using their colour structure. This framework allows one to easily switch results between different Wilson line structures, which is helpful when testing different structures against each other, e.g. when checking universality properties of non-perturbative objects.
Roy-Steiner equations for pion-nucleon scattering
Dozent/Speaker: Dr. Martin Hoferichter
TU Darmstadt - Institut für Kernphysik
Termin/Date: Do. 22.01.2015, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The combination of analyticity, unitarity, and crossing symmetry provides self-consistency constraints for the low-energy phase shifts of pion-nucleon scattering in the form of a system of coupled integral equations. In the talk I will present the status of our solution of these equations and discuss the implications for an improved phenomenological determination of the pion-nucleon sigma term.

Seminare im Jahr 2014

Dispersive approach for three-particle final states interactions: an applications to omega/phi->3pi
Dozent/Speaker: Dr. Igor Danilkin (Jefferson Lab Theory Center, USA)
Termin/Date: Do. 4.12.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will focus my talk on our recent studies of three-body final state interactions: arXiv:1409.7708, 1409.8652. We considered the decays omega/phi -> 3pi in the dispersive framework that is based on the Khuri-Treiman equation. The inelastic contributions were parametrized by the power series in a suitably chosen conformal variable that properly account for the analytic properties of the amplitude. Our results indicated that the final state interactions may be sizable. In my talk the Dalitz plot distributions and integrated decay widths will be presented. As a further application of the formalism I will also discuss the electromagnetic transition form factors of omega/phi -> pi0 gamma*.
Bottom-up holographic approach to QCD
Dozent/Speaker: Prof. Dr. Sergey Afonin (Saint-Petersburg State University)
Termin/Date: Do. 13.11.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: One of the most known result of the string theory consists in the idea that some strongly coupled gauge theories may have a dual description in terms of a higher dimensional weakly coupled gravitational theory - the so-called AdS/CFT correspondence or gauge/gravity correspondence. The attempts to apply this idea to the real QCD are often referred to as "holographic QCD" or "AdS/QCD approach". One of directions in this field is to start from the real QCD and guess a tentative dual higher dimensional weakly coupled field model following the principles of gauge/gravity correspondence. The ensuing phenomenology can be then developed and compared with experimental data and with various theoretical results. Such a bottom-up holographic approach turned out to be unexpectedly successful in many cases. In the given talk, the bottom-up holographic approach to QCD will be explained in detail and a short review of many results will be given.
Exploring the phase structure and dynamics of QCD
Dozent/Speaker: Prof. Dr. Jan Pawlowski (Universität Heidelberg)
Termin/Date: Do. 6.11.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I give an overview on the phase structure of QCD at vanishing and finite temperature and density. Specifically results are discussed for the order parameters of confinement-deconfinement and chiral phase transitions, the nature of these transitions and their interrelation, as well as the thermodynamics of QCD.6The above results are then used for the computation of gluon spectral functions and transport coefficients, i.e. the viscosity over entropy ratio at finite temperature.
Two-cluster scattering on the lattice using the adiabatic projection method and Impurity lattice Monte Carlo.
Dozent/Speaker: Dr. Serdar Elhatisari (Universität Bonn)
Termin/Date: Do. 16.10.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Lattice effective field theory is a powerful numerical method which is formulated in the framework of effective field theory. Recent developments in lattice EFT allow one to study nuclear scattering and reactions. A general framework for calculating scattering and reactions on the lattice the adiabatic projection method. This method uses a set of initial cluster states and Euclidean time projection to give a systematically improvable description of the low-lying cluster states in a finite volume. For large Euclidean time, the set of cluster states span the low-energy subspace of two-cluster continuum states. I present recent lattice Monte Carlo calculations using the adiabatic projection method.
Four-body reactions in nuclear and universal bosonic systems
Dozent/Speaker: Dr. Arnoldas Deltuva ( University of Lisbon, Portugal)
Termin/Date: Do. 13.02.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will review results for four-nucleon scattering and for collisions in the universal four-boson system. They are obtained using four-particle equations for transition operators and solving them in the momentum space framework. Recent progress in three-nucleon e.m. reactions and three-body nuclear reactions will be presented as well.
Electric dipole moment of the nucleon from lattice QCD
Dozent/Speaker: Prof. Dr. Gerrit Schierholz (DESY, Hamburg)
Termin/Date: Do. 6.02.2014, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The electric dipole moment (EDM) of the nucleon provides a unique and sensitive probe to physics beyond the Standard Model. With the increasingly precise experimental efforts to observe the EDM of neutron and proton, it is important to have a rigorous calculation directly from QCD. In this talk first results from a direct simulation at nonvanishing vacuum angle theta are presented.
Insights into the quark Orbital Angular Momentum with experimental prospect
Dozent/Speaker: Dr. Aurore Courtoy (Liege University, Belgium)
Termin/Date: Do. 30.01.2014, 17:15 - 18:45
Ort/Location: NB 6/173
Übersicht/Abstract: We will present a recently analysis of the Generalized Transverse Momentum PDFs (called GTMDs), focusing on parity relations and their relation to the parton Orbital Angular Momentum. In particular, we argue that due to Parity constraints, the helicity combination of GTMDs that describes the configuration of an unpolarized quark in a longitudinally polarized nucleon, can enter the deeply virtual Compton scattering amplitude only through matrix elements involving a final state interaction. The relevant matrix elements in turn involve light cone operators projections in the transverse direction, or they appear in the deeply virtual Compton scattering amplitude at twist three. We show that the twist three contributions associated to orbital angular momentum are related to the target-spin asymmetry in deeply virtual Compton scattering, already measured at HERMES.

Seminare im Jahr 2013

Testing quark forces in baryons using the 1/Nc expansion
Dozent/Speaker: Dr. Carlos Schat (Conicet - University of Buenos Aires)
Termin/Date: Do. 24.10.2013, 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will discuss how a quark model can be matched to the more systematic 1/Nc operator expansion for the masses of excited baryons. Assuming the most general two-body quark-quark interactions two new relations between the masses of L=1 baryons are found. These relations correlate their mixing angles and can be used to test for the presence of three-body forces.
Light Scalar mesons: No ordinary hadrons
Dozent/Speaker: J. R. Peláez(Departamento de Física Teórica II. Universidad Complutense de Madrid)
Termin/Date: Wed. 11-07-2013, 16:00 - 17:30
Ort/Location: NB 6/173
Latest Results from Nuclear Lattice Effective Field Theory
Dozent/Speaker: Prof. Dr. Dean J. Lee ( North Carolina State University, USA)
Termin/Date: Do. 27.06.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: I summarize some of the latest results obtained from applying effective field theory on the lattice to low-energy nuclear physics. Some topics include the spectrum and structure of carbon-12 and oxygen-16, the stellar production of these life-essential elements and the dependence on the fundamental parameters of nature, the ground state energy of nuclei beyond twenty nucleons, the equation of state and pairing gap of neutron matter, and calculations of nuclear scattering and reactions on the lattice.
Nucleon-Nucleon scattering from dispersion relations:  Next-to-leading order study
Dozent/Speaker: Prof. Dr. José Antonio Oller (Universidad de Marcia, Spain)
Termin/Date: Do. 20.06.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: We consider nucleon-nucleon (NN) interactions from Chiral Effective Field Theory applying the N/D method. We calculate the discontinuity of the NN partial-wave amplitudes across the left-hand cut (LHC) by including one-pion exchange (OPE), once-iterated OPE and leading irreducible two-pion exchange (TPE) calculated in Chiral Perturbation Theory (ChPT). We discuss both uncoupled and coupled partial-waves. Phase shifts and mixing angles are typically rather well reproduced, and a clear improvement of the results obtained previously with only OPE is manifest. We also show that the contributions to the discontinuity across the LHC are amenable to a chiral expansion. Our method also establishes correlations between the $S$-wave effective ranges and scattering lengths based on unitarity, analyticity and chiral symmetry.
Nucleon polarizabilities in Compton Scattering
Dozent/Speaker: Dr. Barbara Pasquini (Universita di Pavia, Italy)
Termin/Date: Mi. 8.5.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: The polarizabilities of a composite system such as the nucleon are elementary structure constants, just as its size and shape. The physical content of the nucleon polarizabilities can be visualized best by effective multipole interactions for the coupling of the electric and magnetic fields of a photon with the internal structure of the nucleon. This structure can be accessed by Compton scattering process on the nucleon. In this talk, I will review the current status of theoretical and experimental studies for these observables, and I will introduce the dispersion relations formalism as a powerful tool to extract the polarizabilities from experiments with a minimum of model dependence.
The muonic hydrogen lamb shift and the proton radius
Dozent/Speaker: Prof. Dr. Antonio Miquel Pineda (Universitat Autonoma de Barcelona, Spain)
Termin/Date: Fr. 3.5.2013 , 16:15 - 18:00
Ort/Location: NB 6/173
Übersicht/Abstract: Recently the muonic hydrogen lamb shift has been measured with unprecedented accuracy, allowing for a precise determination of the proton radius. This determination is around 5-7 sigma away from the CODATA value obtained from (mainly) the hydrogen lamb shift and the electron-proton scattering. Within an effective field theory formalism, I will define the proton radius and review the theoretical prediction for the muonic hydrogen lamb shift studying both the pure QED-like computation and the hadronic effects.
Improved description of the p N scattering phenomenology in covariant baryon chiral perturbation theory
Dozent/Speaker: Dr. Jose Manuel Alarcon Soriano (Johannes Gutenberg Universität Mainz, Institut fur Kernphysik)
Termin/Date: Do. 25.04.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: Chiral perturbation theory is an effective field theory of the strong interactions at low energies based on the spontaneous (and explicit) breaking of the chiral symmetry observed in the hadronic spectrum at low energies. While for mesons, identified with the Goldstone bosons, this theory has been very successful, its applicability to the baryonic sector is not so straightforward due to the fact that the baryons are not "soft" particles, like the Goldstone bosons. This has lead to questioning the convergence of chiral perturbation theory with baryons (BChPT) in the physical region. In this seminar I will show how BChPT is able to predict correctly the pion-nucleon scattering phenomenology at low energies, giving results that are in good agreement with independent determinations and solving different problems that questioned the reliability of the theory. This is achieved by combining two important ingredients: the good analytical properties of a relativistic calculation and the explicit contribution of the (1232) resonance. In this way, we are able to connect, for first time in the literature, the information that lies in the physical region, with several subthreshold quantities related to important low energy theorems. This good convergence allowed us to extract, from experimental information, updated values of the pion-nucleon sigma term and the strangeness content of the nucleon. These, in contrast with the old ones, give rise to a new scenario where the sigma-terms are now compatible with updated phenomenology, recent experimental determinations and LQCD calculations.
Operator product expansion in QCD in off-forward kinematics
Dozent/Speaker: Dr. Alexander Manashov (Institut fur Theoretische Physik, Universitat Regensburg)
Termin/Date: Do. 18.04.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: We develop a general approach to the calculation of target mass and finite t = (p'-p)2 corrections in hard processes which can be studied in the framework of the operator product expansion and involve momentum transfer from the initial to the final hadron state. Such corrections, which are usually referred to as kinematic, can be defined as contributions of operators of all twists that can be reduced to total derivatives of the leading twist operators. As the principal result, we provide a set of projection operators that pick up the "kinematic" part of an arbitrary flavor-nonsinglet twist-four operator in QCD. A complete expression is derived for the time-ordered product of two electromagnetic currents that includes all kinematic corrections to twist-four accuracy. The results are immediately applicable to the studies of deeply-virtual Compton scattering, transition γ* -> M γ form factors and related processes.
Pion Distribution Amplitude and Pion-photon transition form factor in sum rules
Dozent/Speaker: Dr. Alexander Pimikov (Dept. Phys., Uni Valencia-CSIC, Spain)
Termin/Date: Do. 11.04.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: We study the pion structure in terms of the pion Distribution Amplitude (DA) and the transition pion-photon form factor in the frameworks of QCD sum rules with nonlocal condensate and light-cone sum rules. A global fit of the pion DA to the data from different collaborations (CELLO, CLEO, BaBar, Belle) on the pion- photon transition form factor is carried out using light-cone sum rules.
The analysis includes the next-to-leading QCD radiative corrections and the twist- four contributions, while the main next-to-next-to-leading term and the twist-six contribution are taken into account in the form of theoretical uncertainties.
Evolution light-like Wilson loops and transverse-momentum dependent parton densities
Dozent/Speaker: Dr. Igor Cherednikov (Uni Antwerpen, Dept. Fysica, Belgium)
Termin/Date: Do. 21.03.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: Connection between the energy evolution of the polygonal light-like Wilson exponentials and the geometry of the loop space is addressed. The renormalization properties and the differential area evolution of these Wilson polygons are studied by making use of the universal Schwinger quantum dynamical approach. The relevance of the dynamical differential equations in the loop space to evolution of the collinear and transverse-momentum dependent parton distribution functions is discussed.
Interface between Theoretical Framework of GPDs and Experimental Measurements of DVCS
Dozent/Speaker: Prof. Dr. Chuen Ji (North Carolina State University, USA)
Termin/Date: Do. 07.03.2013 , 16:00 - 17:30
Ort/Location: NB 6/173
Übersicht/Abstract: Generalized Parton Distributions (GPD)s in Deeply Virtual Compton Scattering (DVCS) have been widely recognized and used as a useful tool to explore the quark and gluon structure of the target hadrons. We discuss the interface between the current theoretical framework based on GPD?s and experiments of DVCS observables. We point out that the present theoretical framework needs to be extended to cover the current and future DVCS experiments. Implications in the Jefferson Lab experiment of DVCS will also be discussed.
Nucleon-nucleon effective field theory with dibaryon fields
Dozent/Speaker: Prof. Dr. Joan Soto (Universitat de Barcelona, Spain)
Termin/Date: Do. 17.01.2013 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will introduce a non-relativistic effective field theory for low energy nucleons that includes explicit dibaryon fields in addition to nucleons and pions. The calculations can be carried out in dimensional regularization and standard minimal subtraction scheme, and hence the power counting becomes explicit. I will present results at NLO and NNLO for the nucleon-nucleon phase shifts in the 1S0 and 3S1-3D1 channels. The outcome is analogous to that of the KSW approach. I will finally show how this effective theory facilitates the resummation of a certain class of diagrams, involving the so called radiation pions, that may give rise to large contributions to the scattering lengths. Recent results on chiral extrapolation formulas for the latter will be presented.
Low-energy few-nucleon reactions in chiral effective field theory
Dozent/Speaker: Dr. Laura Elisa Marcucci (INFN, Pisa)
Termin/Date: Do. 10.01.2013 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Chiral effective field theory (chiEFT) provides a unique opportunity to study nuclear reactions within a framework, where the nuclear Hamiltonian and the nuclear electro-weak transition operators are consistently derived. We have applied such a framework to study muon capture on light nuclei, and we have verified that the calculated total capture rate is in agreement with the available experimental data, as well as with the results obtained in the "old-fashion" potential-model approach. Encouraged by these results, we have applied the same chiEFT framework to study nuclear reactions of astrophysical interest, starting from the pp reaction (p+p --> d + e^+ + nu_e). After reviewing the main aspects of this calculation, I will present the results for the astrophysical S-factor, in a wide energy range (0-100 keV). The astrophysics implications of these results will be discussed. Finally, I will shortly outline the ongoing and future work along this line.

Seminare im Jahr 2012

Photon fusion reactions in a dispersive field theory (DFT) from chiral Lagrangian with vector meson fields
Dozent/Speaker: Dr. Igor Danilkin (Theorie Department GSI, Darmstadt)
Termin/Date: Do. 13.12.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: We study the reactions γγ→π0π0, π+π-, K0bar{K}0, K+K-, η η and π0η based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains 5 unknown parameters that are relevant for the photon fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon fusion data γγ→ π0π0, π+π-, π0η and to the decay η→π0γγ. In order to derive gauge invariant reaction amplitudes in the resonance region constraints from micro-causality and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a0 meson in the π0η channel is dynamically generated and an accurate reproduction of the γγ→ π0η data is achieved up to 1.2 GeV. Based on our parameter sets we predict the γγ→ K0\bar{K}0, K+K-, η η cross sections.
Time-reversal violation in light nuclei in effective field theory
Dozent/Speaker: Dr. Jordy de Vries (University of Groningen, KVI, Niederlande)
Termin/Date: Do. 6.12.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Electric dipole moments (EDMs) break parity and time-reversal (T) symmetry and, by the CPT-theorem, CP-symmetry. If measured they are unambigious signs of new physics, since CP-violation in the quark mixing matrix predict EDMs orders of magnitude away from current experimental limits. The SM also contains the QCD vacuum angle (the theta term) whose value is unknown but strongly limited by neutron EDM experiments. This smallness leaves room for T-violation from physics beyond-the-SM which is expected to exist in order to explain the universal matter/antimatter asymmetry. An open question remains: If an EDM is measured, is it caused by the theta-term or from physics beyond the SM? Triggered by experimental plans to measure the EDMs of light nuclei with unprecedented accuracy in storage rings, this talk will be focused on these systems. After giving an overview of the field of EDMs and the relevant concepts, I will present a framework, based on effective field theories (in particular chiral perturbation theory), in which we calculate light-nuclear EDMs in a consistent framework. I will argue that measurements of a few of these EDMs could point towards the fundamental mechanism of time-reversal violation.
Padé approximation and meromorphization of large N QFT
Dozent/Speaker: Dr. K. Semenov-Tian-Shansky (Liege University)
Termin/Date: Fr. 30.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk we are going to review A. Migdal's approach for planar confining QFT. We discuss the meromorphization procedure which consists in imposing proper analyticity requirements for the set of the Green functions of the theory in order to improve the convergence of the perturbative expansion. Meromorphization procedure generalizes the Padé approximation techniques in the limit of infinite order. It allows to elaborate the set of highly non-trivial restrictions for the physical mass spectrum and the anomalous dimensions of the perturbation theory. We argue that meromorphization, which turns to be an identical transformation of the full theory, may be seen as an interesting working example of matching large N quantum field theory to a dual resonance model and discuss the possible impact of the approach.
The controversy concerning the definition of quark and gluon angular momentum: what's it all about and does it matter?
Dozent/Speaker: Prof. Dr. Elliot Leader (Imperial College, London, UK)
Termin/Date: Do. 29.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: A controversy has arisen as a result of the claim, a few years ago, that all QED textbooks of the past 50 years have been wrong in stating that the photon angular momentum cannot be split into a spin part and an orbital part in a gauge invariant way. The analogue for QCD is important, since we claim to measure the spin of the gluon. I shall give a pedagogical background to the controversy and discuss some of the unexpected issues that have emerged as a consequence, and I shall provide an assessment of the present situation .
Instantons, gluon spin and equivalence principle
Dozent/Speaker: Prof. Dr. Oleg Teryaev (JINR, Dubna)
Termin/Date: Mi. 28.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The absorption of gluon spin in the nucleon to the contribution of Belinfante energy-momentum tensor may be spoiled by the pole in the matrix element of topolgical current. This may lead to the violation of the equivalence principle in the interaction of nucleon spin with gravity and Earth rotation. The realistic alternatives are the nullification of pole contribution or the impossibility to split gluon angular momentum to spin and orbital parts.
High-Accuracy Analysis of Compton Scattering in Chiral EFT: Status and Future
Dozent/Speaker: Prof. Dr. Harald W. Grießhammer ( Institute for Nuclear Studies, Department of Physics, George Washington University, Washington DC, USA)
Termin/Date: Do. 22.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Compton scattering from protons and neutrons provides important insight into the structure of the nucleon. We present a new extraction of the static electric and magnetic dipole polarisabilities of the proton and neutron from all published elastic data below 300 MeV in Chiral Effective Field Theory. Including the Δ(1232) as explicit degrees of freedom is particularly important for the proton above about 100 MeV and for deuteron Compton scattering at >90 MeV as measured at SAL and MAXlab. Consistency arguments dictate including the np-rescattering states and automatically render the correct Thomson limit. We show that the static electric and magnetic scalar polarisabilities of the proton and neutron are identical within the accuracy of available data. In view of ongoing effort at HIγS, MAMI and MAXlab, we address in detail single- and doubly-polarised observables. Several of them can be used to extract not only scalar nucleon polarisabilities, but also the so-far practically un-determined spin-dependent polarisabilities which parameterise the stiffness of the nucleon spin in external electro-magnetic fields. Amongst the questions addressed are: convergence of the expansion when including the Δ and the role of np-rescattering in few-nucleon systems. The next steps in the programme are outlined.
Bound states in a box
Dozent/Speaker: Sebastian König (HISKP (Theorie), Universität Bonn)
Termin/Date: Do. 15.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: When a bound state is put in a finite volume, its mass (energy) is shifted compared to the infinite-volume solution. In the eighties, Lüscher derived an explicit formula for the case of S-wave bound states in a periodic cubic box. In this talk, I will discuss the extension of the formalism to bound states with higher orbital angular momentum. Moreover, I will show how the boundary conditions are changed when one considers bound states in moving frames and how this leads to topological correction factors in the scattering of composite particles. The results have applications to lattice calculations for various kinds of systems.
Issues in the Description of Deeply Virtual Compton Scattering in terms of Generalized Parton Distributions
Dozent/Speaker: Prof. Dr. B.L.G. Bakker ( Vrije Universiteit Amsterdam)
Termin/Date: Do. 8.11.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The amplitudes of Deeply Virtual Compton Scattering (DVCS) can be parametrized in terms of Compton Form Factors (CFFs).The number of CFFs involved is determined by the target spin alone. As an example we discuss the determination of the number of independent from factors for a number of simple cases. Important limitations are provided by Lorentz covariance and electromagnetic gauge invariance. In the scaling regime, the CFFs can be related to Generalized Parton Distributions (GPDs). As the GPDs are directly related to partonic correlators in QCD, it is important to check that the link between CFFs, which are immediately related to the data, and GPDs is precise in the present and planned experiments. A discussion of this issue is given with the conclusion that some open problems still remain.
Chiral corrections to nucleon GPDs
Dozent/Speaker: Alena Moiseeva (TP2, RUB)
Termin/Date: Fr. 26.10.2012 , 14:15 - 15:45
Ort/Location: NB 6/173
Übersicht/Abstract: In a framework of the heavy baryon chiral perturbation theory we obtain the leading chiral corrections to nucleon GPDs. We discuss difficulties of consideration non-local light-cone operators within heavy baryon approach and methods to solve them. We also discuss effects appearing at the scales $x\sim\frac{m_\pi}{M_N}$ and $x\sim\frac{m_\pi^2}{M_N^2}$. We point that being relevant at the region $x\sim1$, the Mellin moments method fails to restore GDPs at those regions of small x.
Loopless neutron EDM and charm CP violation: The Standard Model and beyond
Dozent/Speaker: Prof. Dr. Nikolai Uraltsev (Siegen University and Petersburg NPI)
Termin/Date: Do.25.10.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: It is argued that the electric dipole moment of the neutron in the Standard Model is generated via bound-state physics already at tree level to the second order in the weak interactions. The related contribution has a regular nonvanishing chiral limit and does not depend on the mass splitting between s and d quarks. We estimate it to be about 10^(-31)e*cm. More accurate evaluation is expected within the nucleon description as a soliton of the chiral QCD fields.
If the CP asymmetry in D-> K^+K^- / pi^+pi^- recently reported by LHCb and CDF implies new `milliweak' Delta C=1 interactions beyond those of the SM, this would likewise enhance the above contribution to d_n originating at the charm mass scale. The estimated increase is 30 to 100 times, or even higher in certain model yet not quite natural examples.
Recent Results on Heavy Quarkonium from Belle
Dozent/Speaker: Prof. Dr. Simon Eidelman (Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University)
Termin/Date: Do. 11.10.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Recent results on the heavy quarkonia obtained in the Belle experiment at the KEKB B factory are reported. They include progress in charmonium studies, studies of the h_b(1P,2P) mesons, discovery of the charged states Z_1(10610) and Z_2(10650), observation of the eta_b(1S) and first evidence for the eta_b(2S) state as well as some others.
Ab initio nuclear structure and reactions - perspectives and challenges
Dozent/Speaker: Prof. Dr. James Vary ( Iowa State University, USA)
Termin/Date: Do. 5.7.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The vision of solving the nuclear many-body problem with fundamental interactions tied to QCD via Chiral perturbation theory appears to be gaining credibility. The goals are to preserve the predictive power of the underlying theory, to test fundamental symmetries with the nucleus as laboratory and to develop new understandings of the full range of complex nuclear phenomena.Advances in theoretical frameworks (renormalization and many-body methods) as well as in computational resources (new algorithms and leadership-class parallel computers) signal a new generation of theory simulations that will yield valuable insights into origins of nuclear shell structure, collective phenomena and complex reaction dynamics.I will outline some recent achievements and present ambitious consensus plans along with their challenges for a coming decade of research that will strengthen the links between nuclear theory and nuclear experiment, between nuclear physics and astrophysics, and between nuclear physics and nuclear energy applications.
Effective Theory Evaluation of Correction to Low-Energy Anti-neutrino Proton Scattering
Dozent/Speaker: Prof. Dr. Fred Myhrer (University of South Carolina, USA)
Termin/Date: Mi. 27.6.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Reactor anti-neutrinos are used by the Chooz, Daya Bay and RENO collaborations in order to determine the last neutrino mixing angle, $\Theta_{13}$ from measurements of the inverse neutron beta-decay reaction. If this mixing angle is too small it would be difficult to extract the CP-violating phase in the neutrino mixing matrix. The talk will concentrate on a model independent approach to evaluate the important radiative and recoil corrections necessary to extract an accurate value of $\Theta_{13}$. We will compare these corrections with the ones in neutron beta-decay.
Hadronic parity violation in effective field theory
Dozent/Speaker: Prof. Dr. Mathias Schindler (University of South Carolina, USA)
Termin/Date: Do. 21.6.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The weak interaction between quarks induces a parity-violating component in the nucleon-nucleon interaction. Due to the nonperturbative nature of QCD at low energies, a detailed understanding of how the weak quark-quark interactions manifest themselves in the forces between nucleons remains elusive. Experiments in two-, three-, and few-nucleon systems (including photons) are being performed to map out this weak component of the nuclear force. A theoretical program to analyze and interpret the obtained data based on effective field theory will be described. This approach allows for a systematic and model independent description of two- and few-nucleon observables. Results for parity-violating observables in the two- and three-nucleon sectors will be presented, including a discussion of the relevance of parity-violating three-nucleon interactions.
Effective field theory on the lattice: Ab initio calculations of nuclei and many-body systems
Dozent/Speaker: Prof. Dr. Dean J. Lee (North Carolina State University, USA)
Termin/Date: Do. 14.6.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Effective field theory provides a systematic approach to interacting quantum systems at low energies and densities. Lattice effective field theory combines this approach with non-perturbative lattice methods. I discuss recent applications of lattice effective field theory to the physics of neutron matter and nuclei. I also discuss new developments and ideas in the field.
Gauge invariance and resummations for TMDs
Dozent/Speaker: Dr. Ignazio Scimemi (Complutense University of Madrid,Spain)
Termin/Date: Do. 10.5.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In the past years a lot of work has been devoted to the proper definition of transverse momentum distributions. In this talk I will discuss the problems for gauge invariance of these definitions in the framework of effective field theory of QCD.I will discuss also the use of several regulators and final results for resummation of TMDs at higher orders.
Soft spectator scattering in the nucleon form factors at large Q^2 within the SCET approach
Dozent/Speaker: Dr. Nikolai Kivel (Helmholtz-Institut Mainz)
Termin/Date: Di. 8.5.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: The proton form factors at large momentum transfer are dominated by two contributions which are associated with the hard and soft rescattering respectively. Motivated by a very active experimental form factor program at intermediate values of momentum transfers, $Q^{2}\sim 5-15~\text{GeV}^{2}$, where an understanding in terms of only a hard scattering mechanism cannot yet be expected, we investigate in this work the soft spectator scattering contribution using soft collinear effective theory (SCET). Within such description, the form factor is characterized, besides the hard scale $Q^2$, by a hard-collinear scale $Q \Lambda$, which arises due to presence of soft spectators, with virtuality $\Lambda^2$ ($\Lambda \sim 0.3-0.5$~GeV), such that $Q^{2}\gg Q\Lambda\gg \Lambda^{2}$. In case of nucleon FFs the soft spectator scattering mechanism contributes at leading power accuracy and therefore it must be considered in the systematic QCD factorization approach. We discuss how to generalize the well known Brodsky-Lepage collinear factorization in order to include the soft spectator contribution using the SCET technique. We carefully investigated the factorization of the soft and collinear modes in this case and demonstrate that even for the FF $F_{1}$ the pure collinear factorization could not be valid due to the mixing of the soft and collinear contributions. As a result this allows one to put specific constrains on the end-point behavior of the nucleon distribution amplitude.
Heavy meson molecules in effective field theory
Dozent/Speaker: M. Pavón Valderrama
Termin/Date: Do. 3.5.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: In this talk I want to discuss the role of the one pion exchange potential and heavy quark symmetry in heavy meson molecules such as the X(3872) [1] or the recently discovered Zb (10610) and Zb (10650) [2]. By using techniques developed in atomic physics for handling power-law singular potentials [3,4], which have been also successfully employed in nuclear physics [5], I determine the range of center-of-mass momenta for which the one pion exchange potential is perturbative [6]. In this momentum range, the one pion exchange potential can be considered a subleading order correction, leaving at lowest order a very simple effective field theory consisting only on contact-range interactions (basically X-EFT [7] in the case of the charm sector). In this regard, non-perturbative one pion exchange is only required in the bottom isoscalar sector, a case for which the resulting effective field theory has been analyzed at lowest order for BB* /B*B- molecules in Ref. [8]. I also explore the consequences of heavy quark spin symmetry within a pionless effective field theory approach for the isoscalar charmed meson-antimeson molecules. In particular, I argue that the assumption that the X(3872) is a J P C = 1++ DD* /D*D- molecule implies the existence of a 2 ++D*D* narrow state with an approximate mass of 4012 MeV [9]. Further heavy quark spin symmetry partners of the X(3872) can be deduced if we conjecture the molecular nature of another "XYZ" state, for which we choose the X(3915) resonance [10], leading to the prediction of three new partners with masses of 3710, 3820 and 3955 MeV.

1. Belle Collaboration, Phys.Rev.Lett. 91 (2003) 262001
2. Belle Collaboration, arXiv:1105.4583 and arXiv:1110.2251 [hep-ex]
3. M. Cavagnero, Phys.Rev. A50, 2841 (1994)
4. B. Gao, Phys.Rev. A59, 2778 (1999)
5. M. C. Birse, Phys.Rev. C74, 014003 (2006)
6. M. Pavon Valderrama, arXiv:1204.2400 [hep-ph]
7. S. Fleming, M. Kusunoki, T. Mehen, and U. van Kolck, Phys. Rev. D76, 034006 (2007)
8. J. Nieves, M. Pavon Valderrama, Phys.Rev. D84 (2011) 056015
9. J. Nieves, M. Pavon Valderrama, arXiv:1204.2790 [hep-ph]
10. S. Uehara et al. (Belle), Phys. Rev. Lett. 104 (2010) 092001
New Applications of Renormalization Group Methods in Nuclear Physics
Dozent/Speaker: Dr. Kai Hebeler (The Ohio State University, USA)
Termin/Date: Do. 26.4.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Renewed interest in the physics of nuclei is stimulated by experiments at rare isotope facilities, which open the way to new regions of exotic nuclei, and by astrophysical observations and simulations of neutron stars and supernovae, which require controlled constraints on the equation of state of nucleonic matter. The use of Renormalization Group methods to lower the characteristic resolution of inter-nucleon interactions is opening new avenues for microscopic calculations of low-energy nuclear structure and reactions. I will give an overview over recent developments and discuss various results for the nuclear equation of state and the consequences for the structure of neutron stars, short-range correlations and the role of many-body forces in nuclear systems.
Compton scattering: from deeply virtual to quasi-real
Dozent/Speaker: Dr. Dieter Müller (Ruhr Universität Bochum)
Termin/Date: 24.04.2012
Ort/Location: NB6/173
Übersicht/Abstract: We study deeply virtual Compton scattering at a proposed electron-ion-collider and explore the possible impact of such measurements for the access of generalized parton distributions. In particular we give emphasize to the transverse distribution of sea quarks and gluons and show that such measurements will also provide information on the angular momentum sum rule.
Transverse-Momentum-Dependent Observables: Factorization Theorems And The Relevant Hadronic Matrix Elements
Dozent/Speaker: Dr. Ahmad Idilbi (Universität Regensburg)
Termin/Date: Do. 19.4.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: I will present the theoretical tools needed to address transverse-momentum-dependent observables like the q_t-dependent Higgs boson production spectrum or the analogous Drell-Yan lepton pair production. I will outline how to derive factorization theorems for such observables within an effective field theory techniques. This will lead us to discuss the hadronic matrix elements that appear in such theorems and their properties. If time allows I will perform a comparison with the existing literature on the those topics.
he manifestation of conformal symmetry in QCD and its violation within higher-order perturbation theory
Dozent/Speaker: Prof. Dr. A. L. Kataev (INR, Moskow)
Termin/Date: Mi. 14.3.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: It is known that due to the property of conformal symmetry the basic Crewther relation connects the 3-point function of axial vector-vector-vector fermion currents with the product of two-point function of non-singlet axial-vector fermion currents and the leading twist term of the operator product expansion of two vector currents . The relation between the observable quantities (amplitude of \pi^0\gamma\gamma decay, cross-section of the e^+e^- annihilation to hadrons and deep-inelastic scattering sum rules (Bjorken sum rule, Ellis-Jaffe sum rule and Gross-Llewellyn Smith sum rule) is explained.The current status of studies of various representation of perturbative structures for the conformal symmetry breaking corrections to the Crewther relation for SU(N_c) and U(1) gauge models are discussed. Special attention is paid to the manifestation in these expressions of the conformal anomaly, namely of the factor (\bet(a)/a), where $\beta(a)$ is the perturbative expression for the renormalization group beta-function, defined in the minimal subtractions scheme, or the 't Hooft scheme.
Two-nucleon and three-nucleon systems in three-dimensions
Dozent/Speaker: Prof. Dr. Jacek Golak (Jagiellonian University, Krakow)
Termin/Date: Do. 2.2.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: Recently a new formalism for treating two- and three-nucleon bound states in a three-dimensional approach has been proposed. Starting from the so-called operator forms for the deuteron and triton wave functions, the spin degrees of freedom are removed by suitable operations and only scalar expressions depending on momenta remain. This method can be also extended to nucleon-nucleon scattering, where the nucleon-nucleon t-matrix is represented by six spin-momentum operators accompanied by six scalar functions of momentum vectors. I present the formulation and provide numerical examples for the deuteron and nucleon-nucleon scattering observables. I also show how this new formulation can be used to describe electron scattering off the deuteron. A comparison to results from a standard partial wave decomposition proves the reliability of this new formulation.
Axial anomaly and transition formfactors of pseudoscalar mesons
Dozent/Speaker: Prof. Dr. Oganesian A.G. (ITEP, JINR)
Termin/Date: Do. 26.1.2012 , 16:15 - 17:45
Ort/Location: NB 6/173
Übersicht/Abstract: y use of the dispersive approach to axial anomaly it is shown that the axial anomaly reveals itself as a collective effect of meson spectrum. This allows one to get the relation between possible corrections to continuum and to lower states within QCD method which does not rely on factorization hypothesis. It is shown, relying on the recent data of BaBar collaboration, that the relative non OPE origin corrections to continuum are necessary and even small correction to continuum can dramatically change the pion form factor. In the same approach, the exact non-perturbative QCD sum rule for the transition form factors of $\eta$ and $\eta'$ is obtained. This sum rule allows to express the transition form factors entirely in terms of meson decay constants. It is in a good agreement with experimental data for all $Q^2$.