We compute the renormalized running coupling of SU(3) gauge theory coupled to N f = 2 flavors of massless Dirac fermions in the 2-index-symmetric (sextet) representation. This model is of particular interest as a minimal realization of the strongly interacting composite Higgs scenario. A recently proposed finite volume gradient flow scheme is used. The calculations are performed at several lattice spacings with two different implementations of the gradient flow allowing for a controlled continuum extrapolation and particular attention is paid to estimating the systematic uncertainties. For small values of the renormalized coupling our results for the β-function agree with perturbation theory. For moderate couplings we observe a downward deviation relative to the 2-loop β-function but in the coupling range where the continuum extrapolation is fully under control we do not observe an infrared fixed point. The explored range includes the locations of the zero of the 3-loop and the 4-loop β-functions in the $\overline{MS}$ scheme. The absence of a non-trivial zero in the β-function in the explored range of the coupling is consistent with our earlier findings based on hadronic observables, the chiral condensate and the GMOR relation. The present work is the first to report continuum non-perturbative results for the sextet model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

The running coupling of 8 flavors and 3 colors

We compute the renormalized running coupling of SU(3) gauge theory coupled to N f = 8 flavors of massless fundamental Dirac fermions. The recently proposed finite volume gradient flow scheme is used. The calculations are performed at several lattice spacings allowing for a controlled continuum extrapolation. The results for the discrete β-function show that it is monotonic without any sign of a fixed point in the range of couplings we cover. Finally, as a cross check the continuum results are compared with the well-known perturbative continuum β-function for small values of the renormalized coupling and perfect agreement is found.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Task P: Experimental Particle Physics (Final Report)

The UCSD Elementary Particle Physics group investigates physics at the High Energy Frontier by working exclusively on the CMS experiment at the Large Hadron Collider at CERN. The goal of all four PIs is to discover new facets of the as-yet unwritten laws of nature as a new high-energy regime is opened at the LHC. To that end, we are primarily working on the search for the Higgs boson(s), on the search for supersymmetry, and the search for other new particles and interactions. Further, our goal is to have a very significant intellectual impact on the experiment, as we have in the past. We have played a leading role in the Higgs search in the past and particularly in the observation of a new boson that is consistent with a Higgs-like particle. All four PIs are very involved in the Higgs search. Vivek Sharma was the CMS Higgs co-coordinator during 2010-11. One of our key goals is to measure the properties of this particle as accurately as possible during the upcoming proposal period. The most important modes for this measurement are H 0 → γγ, H 0 → ZZ, and H 0 → WW. We have played leading roles in the measurement of these channels up to now and our goal is to continue work in these channels, measuring the production modes of the “Higgs”, the spin and parity, and the decay branching fractions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗