Theta vacuum in different gauges

TL;DR

This paper refutes recent claims that the physical significance of the theta vacuum angle in QCD-like theories depends on gauge choice, using explicit QED2 constructions to reaffirm the standard view.

Contribution

It critically analyzes and counters recent arguments suggesting gauge dependence of the theta vacuum, reaffirming the gauge invariance of the theta parameter in QCD-like theories.

Findings

Explicit QED2 constructions show gauge independence of theta

Critique of recent claims about gauge-dependent theta significance

Reaffirmation of the standard gauge-invariant understanding

Abstract

In some recent papers it is claimed that the physical significance of the vacuum angle theta for QCD-like theories depends on the chosen gauge condition. We criticise the arguments that were given in support of this claim, and show by explicit construction for the case of QED$_2$ that and why they fail, confirming thereby the commonly accepted point of view.