Representation of spectral functions and thermodynamics

TL;DR

This paper proposes a method to represent spectral functions with a single effective field per quantum channel, avoiding symmetry issues of the resonance approximation, and explores its thermodynamic implications.

Contribution

It introduces a new representation approach for spectral functions that maintains system symmetries and provides thermodynamic analysis.

Findings

Effective field representation avoids symmetry breaking.

Comparison with resonance approximation discussed.

Thermodynamics computed using the new representation.

Abstract

In this paper we study the question of effective field assignment to measured or nonperturbatively calculated spectral functions. The straightforward procedure is to approximate it by a sum of independent Breit-Wigner resonances, and assign an independent field to each of these resonances. The problem with this idea is that it introduces new conserved quantities in the free model (the new particle numbers), therefore it changes the symmetry of the system. We avoid this inconsistency by representing each quantum channel with a single effective field, no matter how complicated the spectral function is. Thermodynamical characterization of the system will be computed with this representation method, and its relation to the independent resonance approximation will be discussed.