Brower, R; Chandrasekharan, S; Negele, JW; Wiese, U-J, *LATTICE QCD AT FIXED TOPOLOGY*,
Phys. Lett. B, vol. 560
(2003),
pp. 64-74 .
**Abstract:**

*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 $\theta$-vacua. We calculate these effects and show how
to extract physical results from numerical data obtained at
fixed topology.*