S parameter and parity doubling below the conformal window

TL;DR

This paper investigates the reduction of the electroweak S parameter in SU(3) gauge theory with six fermions, providing detailed lattice calculations and discussing factors affecting the results, relevant for beyond Standard Model physics.

Contribution

It offers detailed lattice computation methods and insights into parity doubling and finite-volume effects in theories near the conformal window, extending previous findings.

Findings

Reduced S parameter observed in Nf=6 fermion theory

Finite-volume effects influence lattice results

Results support parity doubling near the conformal window

Abstract

Recently the Lattice Strong Dynamics Collaboration reported a reduction of the electroweak S parameter for SU(3) gauge theory with Nf=6 fermions in the fundamental representation, compared to scaled-up QCD (arXiv:1009.5967). Here I provide additional details of our calculation. I discuss our use of conserved lattice currents; the relation to vector--axial parity doubling; finite-volume effects; and the sensitivity of our results to the number of fermion doublets with chiral electroweak couplings. Results presented here include additional data, and do not affect our previously-published conclusions.