Role of the $\sigma$-resonance in determining the convergence of chiral perturbation theory

TL;DR

This paper investigates how the light $\sigma$-resonance affects the convergence of chiral perturbation theory in a lattice gauge model, highlighting the importance of the resonance's mass in theoretical predictions.

Contribution

It demonstrates the impact of a light $\sigma$-resonance on chiral perturbation theory convergence using a lattice model with QCD-like symmetries, providing insights relevant for lattice QCD.

Findings

Chiral low energy constants are consistent between $p$-regime and $\e$-regime.

Chiral perturbation theory is accurate for $\xi \,<\, 0.002$ within 1%.

Deviations occur for $\xi \,>\, 0.0035$ due to the light $\sigma$-resonance.

Abstract

The dimensionless parameter $\xi = M_\pi^2/(16 \pi^2 F_\pi^2)$, where $F_\pi$ is the pion decay constant and $M_\pi$ is the pion mass, is expected to control the convergence of chiral perturbation theory applicable to QCD. Here we demonstrate that a strongly coupled lattice gauge theory model with the same symmetries as two-flavor QCD but with a much lighter $\sigma$-resonance is different. Our model allows us to study efficiently the convergence of chiral perturbation theory as a function of $\xi$. We first confirm that the leading low energy constants appearing in the chiral Lagrangian are the same when calculated from the $p$-regime and the $\epsilon$-regime as expected. However, $\xi \lesssim 0.002$ is necessary before 1-loop chiral perturbation theory predicts the data within 1%. For $\xi > 0.0035$ the data begin to deviate dramatically from 1-loop chiral perturbation theory predictions. We argue that this qualitative change is due to the presence of a light $\sigma$-resonance in our model. Our findings may be useful for lattice QCD studies.