Further studies of QCD with sextet quarks

TL;DR

This study investigates the finite-temperature behavior of QCD with sextet quarks to determine if it exhibits walking or conformal dynamics, using lattice simulations at different temporal extents.

Contribution

It provides new lattice simulation data comparing 2-flavour and 3-flavour sextet quark theories to distinguish between walking and conformal behaviors.

Findings

2-flavour theory shows a decreasing coupling, suggesting walking behavior.

3-flavour theory's coupling decrease indicates simulations are not yet at large enough N_t.

Preliminary results suggest deviations from asymptotic freedom predictions.

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 $N_t \rightarrow \infty$ and hence the lattice spacing $a \rightarrow 0$ 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 $N_t$.