title: Susceptibility of the QCD vacuum to CP-odd electromagnetic background fields.
abstract: We investigate two flavor quantum chromodynamics (QCD) in the presence of CP-odd electromagnetic background fields and determine, by means of lattice QCD simulations, the induced effective θ term to first order in E[over →] · B[over →]. 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, and then exploit the analytic continuation. Our results are relevant to a description of the effective pseudoscalar quantum electrodynamics-QCD interactions.
authors.affiliation: Dipartimento di Fisica, dell'Università di Pisa and INFN-Sezione di Pisa, Largo Pontecorvo 3, I-56127 Pisa, Italy. delia@df.unipi.it
authors.forename: Massimo
authors.initials: M
authors.lastname: D'Elia
authors.forename: Marco
authors.initials: M
authors.lastname: Mariti
authors.forename: Francesco
authors.initials: F
authors.lastname: Negro