A surprise with many-flavor staggered fermions in the strong coupling limit

TL;DR

This study uses Monte Carlo simulations to challenge the traditional view that chiral symmetry is always broken at strong coupling in staggered fermions, revealing a phase transition to a conformal phase at high flavor numbers.

Contribution

It demonstrates that chiral symmetry restoration occurs at strong coupling for many flavors, connecting lattice results with continuum conformal window predictions.

Findings

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

The chirally symmetric phase exhibits scale invariance with observables scaling with system size.

The phase diagram of lattice QCD is conjectured as a function of coupling and flavor number.

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 and the Dirac spectrum. We find that all observables scale with L, which 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.