Since present Monte Carlo algorithms for lattice QCD may become trapped in a fixed topological charge sector, it is important to understand the effect of calculating at fixed topology. In this work, we show that although the restriction to a fixed topological sector becomes irrelevant in the infinite volume limit, it gives rise to characteristic finite size effects due to contributions from all θ-vacua. We calculate these effects and show how to extract physical results from numerical data obtained at fixed topology.
@article{arxiv.hep-lat/0302005,
title = {QCD at Fixed Topology},
author = {R. Brower and S. Chandrasekharan and J. Negele and U. -J. Wiese},
journal= {arXiv preprint arXiv:hep-lat/0302005},
year = {2008}
}