Further studies of QCD with sextet quarks

Abstract

We continue our simulations of QCD with 2 flavours of colour-sextet quarks as a model for walking technicolor. QCD with 3 flavours of colour-sextet quarks is also studied for comparison with the 2-flavour theory. We simulate these theories at finite temperatures T, using lattices with a finite extent $N_{t}a=1/T$ in the (Euclidean) time direction. The lattice coupling at the chiral-symmetry-restoration transition is measured as a function of $N_t$. If this is indeed a finite-temperature transition, the evolution of this coupling with $N_t$ as $N_t\to \infty$ and hence the lattice spacing $a\to 0$ should be described by asymptotic freedom. If so, the theory is QCD-like and walking. If, however, this coupling approaches a constant non-zero value in the large $N_t$ limit, the transition is a bulk transition and the continuum theory is conformal. For the 2-flavour theory, the coupling does show a significant decrease between $N_t=8$ and $N_t=12$, favouring the walking scenario. However, preliminary results are that the change is less than that predicted by asymptotic freedom. For the 3-flavour case, which is expected to be conformal, there is still a significant decrease in the coupling between $N_t=6$ and $N_t=8$, indicating that we are not yet at large enough $N_t$.

Comments: Latex, 7 pages, 4 postscript figures. Presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, Germany and at Origin of Mass 2013, August 5 to August 22, 2013, Odense, Denmark