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Seminare im Jahr 2017

Seminare in früheren Jahren

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 https://arxiv.org/abs/1704.01114 ], 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