Particle Theory Seminars

The particle theory seminars are organized by the Theory Group of the Laboratory for Particle Physics (LTP) at PSI.

The next seminar will take place on Friday, June 20, at 11:15 AM in WBGB/019.

Speaker: Eleftheria Solomonidi (IFIC, Universitat de València)

Title: Rare charm decays with cascade topologies & implications for CP violation

Abstract

The CP violation observed in the hadronic decays of charmed mesons remains a puzzling open question for theorists. Calculations relying on the assumption of inelastic final-state interactions occurring between the pairs of pions and kaons fall short of the experimental value. It has been pointed out that a third channel of four pions can leave imprints on the CP asymmetries of the two-body decays. At the same time, plenty of data are available for rare decays such as D⁰ → π⁺π^-l⁺l^-, which provide a promising environment for the search for new physics. With this motivation, we study the cascade topology D⁰ → a₁(1260)⁺( → ρ(770)⁰ π⁺) π^-, which has been measured to contribute significantly to the 4π decays of the same meson, and estimate its effect on the branching ratio of the rare decays. I will also comment on the possibility of this topology contributing to the decay amplitude of D⁰ → π⁺π^- and by extension to the related CP asymmetry.

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The last seminar took place on Thursday, March 20, at 11:00 AM in WBGB/020.

Speaker: Eirini Lymperiadou (HISKP, University of Bonn)

Title: A model for light tensor meson transition form factors

Abstract

This work deals with the construction of a mostly dynamical approach for the derivation of tensor meson transition form factors (TFFs). The specific case of the a2(1320) tensor meson is examined in the context of the hadronic light-by-light (HLbL) term of the anomalous magnetic moment of the muon a_μ. The goal is to provide a TFF description that will minimize the uncertainties introduced due to model dependencies, approximation and the scarcity of data for this case. The constructed framework and the calculations performed will be presented along with the utilized theoretical concepts, such as dispersion relations, left-hand cuts and the Passarinio-Veltman decomposition. 
 

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The following seminar took place on Friday, February 21 at 11:30 AM in WHGA/121

Speaker: Lisa Biermann (PSI)

Title: Aspects of the Electroweak Phase Transition

Abstract

The hot early universe might have been in a different ground state than our universe today. This opens the possiblity that our universe transitioned from a high-temperature vacuum (which for example restores the electroweak symmetry) to the low-temperature vacuum of today in which the electroweak symmetry is spontaneously broken via an electroweak phase transition (EWPT). Models beyond the Standard Model (BSM) can (unlike the Standard Model) encorporate a (strong) first-order EWPT while also reproducing all experimental collider data. This additional possibility of a strong first-order EWPT can then serve as the required departure from thermal equilibrium, allowing to explain the observed matter-antimatter asymmetry of the universe at the electroweak scale. Furthermore, a first-order EWPT sources a stochastic gravitational wave background to which e.g. the future space-bound gravitational wave observatory LISA might become sensitive.

In this talk, I will dive into finite-temperature field theory and present several BSM extensions of the scalar sector that allow for first-order electroweak phase transitions, as well as observable gravitational waves. I will highlight how EWPTs position these models at the intersection of collider phenomenology and cosmology, i.e. how they are tested from these two perspectives.