Dear All,

We have the pleasure of inviting you to the Particle Theory Seminar on Tuesday, January 16  at 12:15, which will be given by

Michał Iglicki (Chalmers University of Technology)

entitled

„In-medium regularization of t-channel singularities of scattering processes".

Abstract:

Let us consider a 2-2 scattering process described by a t-channel diagram. If the mediator (the intermediate t-channel state) is kinematically allowed to be on mass-shell (p^2 = m^2), the matrix element suffers from a singularity caused by vanishing denominator of the Feynman propagator. It is then impossible to calculate the reaction rate, making it hard to obtain any quantitative predictions of, e.g., a given model of beyond-SM physics. Usually, to cure this issue, one uses the resummed propagator instead of the bare one. Then, the mediator's decay width provides a non-zero imaginary contribution to the denominator of the on-shell propagator, regularizing the singularity. Even if the mediator is stable (which is often the case in processes involving hypothetical dark particles), it can acquire an effective decay width due to interactions with particles forming the environment (medium) of the process. In such a case, the above method can still be employed. In my talk, I will provide a strict set of conditions for a given process to be affected by the singularty. I will also present and discuss results for the medium-induced effective width calculated for mediator of spin 0, 1/2 or 1. The discussion will be illustrated with examples coming from analysis of the so-called vector-fermion dark matter model.

(based on DOI:10.1007/JHEP06(2023)006, 10.1016/j.nuclphysb.2022.115967)

The speaker will be on-line, local participants are invited to meet in the seminar room D-2-02.