Theta vacuum
= Theta vacuum
{title2=$|\theta\rangle$}
{wiki}
A theta vacuum is a coherent state $|\theta\rangle=\sum_n e^{in\theta}|n\rangle$ formed from gauge vacua of different winding numbers. Large gauge transformations shift $n$ and act on this state by a phase. The <Yang-Mills theta term> gives the corresponding weighting of spacetime topological sectors.