Excited-state contribution to the axial-vector and pseudo-scalar correlators with two extra pions

Understand

We study multi-particle state contributions to the QCD two-point functions of the axial-vector and pseudo-scalar quark bilinears in a finite spatial volume.

• For sufficiently small quark masses one expects three-meson states with two additional pions at rest to have the lowest total energy after the ground state.
• We calculate this three-meson state contribution using chiral perturbation theory.
• We find it to be strongly suppressed and too small to be seen in present-day lattice simulations.