The S Parameter in QCD from Domain Wall Fermions

TL;DR

This paper computes the S parameter in QCD using lattice simulations with Domain Wall Fermions, providing a test for methods applicable to beyond Standard Model theories and comparing results with experimental data.

Contribution

It introduces a lattice QCD calculation of the S parameter and pion mass splitting using Domain Wall Fermions, linking QCD results to electroweak precision constraints.

Findings

S(mH=120GeV) = 0.42(7) in agreement with previous results

Pion mass splitting consistent with experimental values

Method serves as a test for beyond Standard Model theories

Abstract

We have computed the SU(2) Low Energy Constant l5 and the mass splitting between charged and neutral pions from a lattice QCD simulation of nf = 2 + 1 flavors of Domain Wall Fermions at a scale of a-1 = 2.33GeV. Relating l5 to the S parameter in QCD we obtain a value of S(mH=120GeV) = 0.42(7), in agreement with previous determinations. Our result can be compared with the value of S from electroweak precision data which constrains strongly interacting models of new physics like Technicolor. This work in QCD serves as a test for the methods to compute the S parameter with Domain Wall Fermions in theories beyond the Standard Model. We also infer a value for the pion mass splitting in agreement with experiment.