Real-Time thermal Ward-Takahashi Identity for vectorial current in QED and QCD

TL;DR

This paper proves the Ward-Takahashi identity at finite temperature and chemical potential for QED exactly and approximately for QCD, providing thermal constraints on fermion propagators relevant for physical processes.

Contribution

It offers a rigorous proof of the thermal Ward-Takahashi identity for QED and an approximate proof for QCD using the canonical operator approach.

Findings

Thermal WTI constrains the imaginary part of inverse fermion propagator.

At zero temperature and chemical potential, WTI reduces to its standard form.

Provides a practical example illustrating the application of thermal WTI.

Abstract

It is shown that, by means of canonical operator approach, the Ward-Takahashi identity (WTI) at finite temperature $T$ and finite chemical potential $\mu$ for complete vectorial vertex and complete fermion propagator can be simply proven, rigorously for Quantum Electrodynamics (QED) and approximately for Quantum Chromodynamics (QCD) where the ghost effect in the fermion sector is neglected. The WTI shown in the real-time thermal matrix form will give definite thermal constraints on the imaginary part of inverse complete Feynman propagator including self-energy for fermion and will play important role in relevant physical processes. When the above inverse propagator is assumed to be real, the thermal WTI will essentially be reduced to its form at $T=\mu=0$ thus one can use it in the latter's form. At this point, a practical example is indicated.