Large Gauge Transformations and the Light-Front Vacuum Structure

TL;DR

This paper investigates residual gauge symmetries in light-front gauge theories, revealing vacuum degeneracy and coherent states, and discusses implications for the structure of the quantum vacuum, including potential extensions to more complex theories.

Contribution

It demonstrates how residual gauge symmetries lead to vacuum degeneracy and coherent states in light-front quantized theories, providing a new perspective on vacuum structure without a Dirac sea.

Findings

Unitary operators generate degenerate coherent-state vacua.

Fermionic vacuum component emerges naturally without Dirac sea.

Discussion of theta-vacuum in the massive Schwinger model.

Abstract

A residual gauge symmetry, exhibited by light-front gauge theories quantized in a finite volume, is analyzed at the quantum level. Unitary operators, which implement the symmetry, transform the trivial Fock vacuum into an infinite set of degenerate coherent-state vacua. A fermionic component of the vacuum emerges naturally without the need to introduce a Dirac sea. The vacuum degeneracy along with the derivation of the theta-vacuum is discussed within the massive Schwinger model. A possible generalization of the approach to more realistic gauge theories is suggested.