Effects of staggered fermions and mixed actions on the scalar correlator

TL;DR

This paper provides analytic predictions for the scalar correlator in lattice QCD with staggered and mixed actions, highlighting the effects of taste breaking and unphysical intermediate states on the scalar meson mass extraction.

Contribution

It introduces the calculation of the bubble contribution to the scalar correlator within Staggered and Mixed Chiral Perturbation Theory, accounting for taste breaking effects.

Findings

The bubble contribution's effective mass is below M_pi+M_eta due to taste breaking.

The scalar correlator can become negative with mixed quark actions when tuning quark masses.

Unphysical intermediate states influence the scalar correlator at small quark masses.

Abstract

We provide the analytic predictions for the flavor non-singlet scalar correlator, which will enable determination of the scalar meson mass from the lattice scalar correlator. We consider simulations with 2+1 staggered sea quarks and staggered or chiral valence quarks. At small u/d masses the correlator is dominated by the bubble contribution, which is the intermediate state with two pseudoscalar mesons. We determine the bubble contribution within Staggered and Mixed Chiral Perturbation Theory. Its effective mass is smaller than the mass M_pi+M_eta, which is the lightest intermediate state in proper 2+1 QCD. The unphysical effective mass is a consequence of the taste breaking that makes possible the intermediate state with mass 2*M_pi. We find that the scalar correlator can be negative in the simulations with mixed quark actions if the sea and valence quark masses are tuned by matching the pion masses M_{val,val}=M_{pi_5}.