Theorie Palaver

Programm für das Wintersemester 2022/2023

Tuesdays, 14:00 Uhr s.t.

Institut für Physik
Lorentz room (Staudingerweg 7, 5th floor)
live at Zoom

08.11.22Cem Eröncel, DESY
Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it has been subject to extensive theoretical and experimental research in recent years. The most popular ALP production mechanism studied in the literature is the misalignment mechanism, where the ALP field initially has negligible kinetic energy and starts oscillating when its mass becomes comparable to the Hubble scale. Recently, a new mechanism called Kinetic Misalignment has been proposed where the ALP field receives large kinetic energy at early times due to the explicit breaking of the Peccei-Quinn symmetry. This causes a delay in the onset of oscillations so that the ALP dark matter parameter space can be expanded to lower values of the axion decay constant. At the same time, the ALP fluctuations grow exponentially via parametric resonance in this setup, and most of the energy in the homogeneous mode is converted to ALP particles. This process is known as fragmentation. In this talk, I will discuss the observational consequences of fragmentation for the axion mini-clusters and show that a sizable region of the ALP parameter space can be tested by future experiments that probe the small-scale structure.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

11.11.22Pere Masjuan, Universitat Autonoma de Barcelona
The role of Pade approximants as fitting functions
15:00 Uhr s.t., HIM building, room 02.111

Note the special time and room.

15.11.22Mathias Becker, JGU Mainz
A non-minimal dark sector could explain why WIMP dark matter has evaded detection so far. Based on the extensively studied example of a simplified t-channel dark matter model involving a colored mediator, we demonstrate that the Sommerfeld effect and bound state formation must be considered for an accurate prediction of the relic density and thus also when inferring the experimental constraints on the model. We find that parameter space thought to be excluded by LHC searches and direct detection experiments still remains viable. Moreover, we point out that the search for bound state resonances at the LHC offers a unique opportunity to constrain a wide range of dark matter couplings inaccessible to prompt and long-lived particle searches.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor)

22.11.22Alfredo Guerrera, Padua U. and INFN
Axion--Like--Particles are among the most economical and well motivated extensions of the Standard Model. In this talk ALP production from hadronic and leptonic meson decays are studied. The hadronization part of these decay amplitudes has been obtained using Brodsky--Lepage method or LQCD, at needs. In particular, the general expressions for ALP emission in mesonic s-- and t--channel tree--level processes are thoroughly discussed, for pseudoscalar and vector mesons. Accordingly, exact results as well as some useful approximation for meson-to-meson and meson leptonic decay amplitudes are presented. I will the discuss the phenomenology of various decays and highlight the most robust in terms of experimental searches and theoretical predictions. Finally, bounds on the (low--energy effective Lagrangian) ALP--fermion couplings are derived, from present and future flavour experiments. If I have time left I'll also cover some of the new form factors calculations in B mesogenesis.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom


29.11.22Markus Fröb, U. Leipzig

Perturbative Quantum Gravity: Diffeomorphisms, Observables and Noncommutativity 

Perturbative Quantum Gravity (pQG), the effective quantum field theory of gravitational fluctuations around a given background, is currently the only experimentally accessible theory of quantum gravity. Its tree-level predictions, in the form of temperature fluctuations of the Cosmic Microwave Background, have been experimentally confirmed, and it is possible that loop corrections are accessible to future experiments. However, while the tree-level results are well understood also from a theoretical point of view, the diffeomorphism symmetry of gravity makes the construction of invariant observables very difficult beyond this. Only recently, this issue has been overcome, and a class of causal invariant observables has been constructed. I will discuss this construction and how it can be related to observations, and present some predictions of pQG for graviton loop corrections to the Newtonian gravitational potential and the Hubble rate, the local expansion rate of the universe. Lastly, I show that pQG also predicts that spacetime becomes non-commutative at the Planck scale, but in a different way from previous approaches. The talk is based (in particular) on the recent papers arXiv:1806.11124, 2108.11960, 2109.09753 and 2207.03345.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

zukünftige Termine
06.12.22Johanna Erdmenger, Würzburg U.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

07.02.23Weiguang Jiang, JGU Mainz
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

Koordination: Kontakt:

Dr. Anke Biekötter

Dr. Philipp Böer

Dr. Enrico Morgante