Conformality in many-flavour lattice QCD at strong coupling

TL;DR

This study challenges the traditional view that chiral symmetry is always broken at strong coupling in lattice QCD, showing instead that with many flavors, a chirally symmetric, conformal phase emerges, which can be studied via lattice simulations.

Contribution

The paper demonstrates, through Monte Carlo simulations, that chiral symmetry can be restored at strong coupling for many flavors, revealing a conformal phase connected to continuum QCD.

Findings

Chiral symmetry is restored via a first-order transition at high flavor numbers.

The chirally symmetric phase exhibits IR-conformality with all masses vanishing as 1/L.

The strong-coupling phase provides a useful setting to study IR-conformal behavior.

Abstract

It is widely believed that chiral symmetry is spontaneously broken at zero temperature in the strong coupling limit of staggered fermions, for any number of colors and flavors. Using Monte Carlo simulations, we show that this conventional wisdom, based on a mean-field analysis, is wrong. For sufficiently many fundamental flavors, chiral symmetry is restored via a bulk, first-order transition. This chirally symmetric phase appears to be analytically connected with the expected conformal window of many-flavor continuum QCD. We perform simulations in the chirally symmetric phase at zero quark mass for various system sizes L, and measure the torelon mass, the Dirac spectrum and the hadron spectrum. All masses go to zero with 1/L. L is hence the only infrared length scale. Thus, the strong-coupling chirally restored phase appears as a convenient laboratory to study IR-conformality. Finally, we present a conjecture for the phase diagram of lattice QCD as a function of the bare coupling and the number of quark flavors.