Large Gauge Transformations and the Light-Front Vacuum Structure
  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. 
L. Martinovic (Institute of Physics, Bratislava)