Susceptibility of the QCD vacuum to CP-odd electromagnetic background fields

TL;DR

This study uses lattice QCD simulations to explore how CP-odd electromagnetic fields influence the QCD vacuum, revealing the induced effective theta term and its implications for pseudoscalar interactions.

Contribution

It provides the first lattice QCD determination of the induced theta term in the presence of CP-odd electromagnetic backgrounds, using a novel analytic continuation approach.

Findings

Induced effective theta term is proportional to the scalar product of E and B fields.

Results are obtained at lattice spacings down to 0.1 fm and pion masses around 480 MeV.

The study offers insights into pseudoscalar QED-QCD interactions.

Abstract

We investigate two flavor QCD in presence of CP-odd electromagnetic background fields and determine, by means of lattice QCD simulations, the induced effective theta term to the first order in the scalar product of E and B. We employ a rooted staggered discretization and study lattice spacings down to 0.1 fm and Goldstone pion masses around 480 MeV. In order to deal with a positive measure, we consider purely imaginary electric fields and real magnetic fields, then exploiting analytic continuation. Our results are relevant to a description of the effective pseudoscalar QED-QCD interactions.