QCD and the eta prime Mass: Instantons or Confinement?

TL;DR

This paper proposes using lattice QCD with two colors at non-zero baryon density to distinguish whether instantons or confinement primarily generate the eta prime mass, offering a new approach to understanding non-perturbative QCD effects.

Contribution

It introduces a novel method to differentiate instanton effects from confinement in eta prime mass generation using lattice calculations in two-color QCD at finite density.

Findings

Instanton density varies with density, affecting eta prime mass.

Lattice results at high density can test instanton predictions.

Finite isospin density QCD can shed light on OZI-violation mechanisms.

Abstract

We argue that lattice calculations of the $\eta'$ mass in QCD with $N_c=2$ colors performed at non-zero baryon chemical potential can be used to study the mechanism responsible for the mass of the $\eta'$. QCD with two colors is an ideal laboratory because it exhibits confinement, chiral symmetry breaking and a would-be $U(1)_A$ Goldstone boson at all densities. Since the instanton density and the confinement scale vary with density in a very different way, instantons are clearly distinguishable from other possible mechanisms. There is an instanton prediction for the $\eta'$ mass at large density that can be compared to lattice results. The density dependence of the instanton contribution is a simple consequence of the integer topological charge carried by the instanton. We also argue that $N_c=3$ color QCD at finite isospin density can be used in order to study the origin of OZI-violation in the scalar sector.