Photon emissivity in the vicinity of a critical point - A case study within the quark meson model

TL;DR

This paper investigates how photon emission rates are affected by the phase structure near a critical point in the quark meson model, highlighting the influence of phase transitions and effective masses on emissivity.

Contribution

It provides a case study linking phase transition features with photon emissivity using the quark meson model, emphasizing the role of effective masses and thermodynamics.

Findings

Photon emissivities strongly depend on effective masses of particles.

First-order phase transitions significantly alter photon emission rates.

Thermodynamic properties are closely linked to emission rates.

Abstract

The quark meson (linear sigma) model with linearized fluctuations displays at a critical end point the onset of a curve of first-order phase transitions (FOPTs) located at non-zero chemical potentials and temperatures below a certain cross-over temperature. The model qualifies well for an illustrative example to study the impact of the emerging FOPT, e.g. on photon emissivities. Such a case study unravels the tight interlocking of the phase structure with the emission rates, here calculated according to lowest-order tree level processes by kinetic theory expressions. It is the strong dependence of the rates on the effective masses of the involved degrees of freedom which distinctively vary over the phase diagram thus shaping the emissivity accordingly. At the same time, thermodynamic properties of the medium are linked decisively to these effective masses, i.e. a consistent evaluation of thermodynamics, governing for instance adiabatic expansion paths, and emission rates is maintained within such an approach.