Thermodynamics of lattice QCD with 2 sextet quarks on N_t=8 lattices

TL;DR

This study investigates the thermodynamics of lattice QCD with 2 sextet quarks on N_t=8 lattices, exploring the nature of the chiral transition and its implications for walking technicolor theories.

Contribution

It extends lattice simulations to N_t=8, providing new data on the chiral transition and its scaling behavior, crucial for understanding conformal or walking dynamics.

Findings

Both deconfinement and chiral transitions move to weaker couplings with increasing N_t.

The change in the chiral transition coupling from N_t=6 to 8 is smaller than from 4 to 6.

Results suggest the need for larger N_t to determine if the theory exhibits walking behavior.

Abstract

We continue our lattice simulations of QCD with 2 flavours of colour-sextet quarks as a model for conformal or walking technicolor. A 2-loop perturbative calculation of the $\beta$-function which describes the evolution of this theory's running coupling constant predicts that it has a second zero at a finite coupling. This non-trivial zero would be an infrared stable fixed point, in which case the theory with massless quarks would be a conformal field theory. However, if the interaction between quarks and antiquarks becomes strong enough that a chiral condensate forms before this IR fixed point is reached, the theory is QCD-like with spontaneously broken chiral symmetry and confinement. However, the presence of the nearby IR fixed point means that there is a range of couplings for which the running coupling evolves very slowly, i.e. it 'walks'. We are simulating the lattice version of this theory with staggered quarks at finite temperature studying the changes in couplings at the deconfinement and chiral-symmetry restoring transitions as the temporal extent ($N_t$) of the lattice, measured in lattice units, is increased. Our earlier results on lattices with $N_t=4,6$ show both transitions move to weaker couplings as $N_t$ increases consistent with walking behaviour. In this paper we extend these calculations to $N_t=8$. Although both transition again move to weaker couplings the change in the coupling at the chiral transition from $N_t=6$ to $N_t=8$ is appreciably smaller than that from $N_t=4$ to $N_t=6$. This indicates that at $N_t=4,6$ we are seeing strong coupling effects and that we will need results from $N_t > 8$ to determine if the chiral-transition coupling approaches zero as $N_t \rightarrow \infty$, as needed for the theory to walk.