Chiral Perturbation Theory with an Isosinglet Scalar

TL;DR

This paper extends chiral perturbation theory to include an isosinglet scalar, analyzing its effects on low-energy constants and fitting lattice data in near-conformal BSM models.

Contribution

It introduces a novel extension of chiral perturbation theory incorporating an isosinglet scalar and applies it to lattice data in near-conformal theories.

Findings

Calculated one-loop corrections to pion mass, decay constant, and scalar mass.

Fitted the extended theory to lattice data for SU(3) with Nf=8.

Demonstrated phenomenological relevance of scalar effects in near-conformal models.

Abstract

We present an extension of chiral perturbation theory that explicitly includes an isosinglet scalar in the Lagrangian. The dynamical effects from the scalar state is of phenomenological relevance in theories where the mass of the isosinglet scalar is comparable to the mass of the pseudo-Goldstone bosons. This near-degeneracy of states is for example observed in certain near-conformal BSM models. From the Lagrangian we calculate the one-loop radiative corrections to the pion mass, the pion decay constant, and the scalar mass. We then proceed and use the results to fit numerical lattice data for an SU(3) gauge theory with $N_f=8$ light flavours in the fundamental representation.