S parameter news and updates

Summary

This project aims to extract the value of the Peskin-Takeuchi S parameter from lattice gauge theory. We use domain wall lattices to work in a fully self-consistent formulation with chiral fermions. We have posted at arXiv:1009.5967 initial results for 2-flavor and 6-flavor ensembles of gauge configurations generated by the LSD Collaboration, which have been submitted to PRL for publication.

Our 2-flavor results verify recent calculations of S in QCD (PRL 101:242001, 2008 and PRD 81:014504, 2010), and our 6-flavor results reveal a reduction in the S parameter per electroweak doublet, compared to the 2-flavor theory. This offers the first nonperturbative evidence from first-principles calculations that many-flavor "walking technicolor" models of electroweak symmetry breaking may produce a phenomenologically viable S parameter.

Currently we are using the USQCD clusters at Jlab as well as NSF Teragrid resources to accumulate additional statistics from the 2- and 6-flavor LSD ensembles, before turning to 10-flavor ensembles being generated by the LSD Collaboration at Livermore National Lab.

Project status as of 12 October 2010

• Implementation of a mixed-precision domain wall inverter in early 2010 significantly improved the code performance.
• Initial results posted at arXiv:1009.5967, submitted to PRL.
• Additional statistics are being accumulated using the USQCD clusters at Jlab and NSF Teragrid resources.