QCD with colour-sextet quarks

We study QCD with 2 colour-sextet quarks as a model for walking Technicolor, using lattice gauge theory simulations (RHMC) at finite temperature. Our goal is to determine if the massless theory is QCD-like (confining, with spontaneously-broken chiral symmetry) with a slowly varying coupling (walks) or if it is a conformal field theory. We do this by simulating the theory at finite temperature and observing how the coupling at the chiral-symmetry restoration temperature depends on the temporal extent $N_t$ of the lattice (in lattice units). If the theory is QCD-like, this coupling should approach zero in the large $N_t$ limit in the manner predicted by asymptotic freedom. If it is conformal, this coupling should approach a finite value in this limit, i.e. the transition would be a bulk transition. We discuss new results at $N_t=6,8$ and 12. These preliminary results indicate that the coupling does decrease with increasing $N_t$, but it is unclear if this is consistent with asymptotic freedom.

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