Theta vacuum physics from QCD at fixed topology

TL;DR

This paper introduces a method to extract physical quantities in the theta vacuum from fixed topology data, accounting for finite size effects, and demonstrates how to measure topological susceptibility via pseudoscalar correlators.

Contribution

It derives a general formula for finite size corrections in fixed topology simulations and shows how to measure topological susceptibility from two-point functions.

Findings

Finite size effects can be corrected using the derived formula.

Topological susceptibility can be obtained from pseudoscalar two-point functions.

The method extends previous work by Brower et al. to arbitrary correlators.

Abstract

We propose a method to obtain physical quantities in the theta vacuum from those at fixed topology, which are different by finite size effects. Extending the work by Brower et al., we derive the formula to estimate these finite size corrections for arbitrary correlators in terms of the topological susceptibility and the theta dependence. Applying this formula, we show that topological susceptibility can be measured through two-point functions of pseudoscalar operator.