Quark mass dependence of two-flavor QCD

TL;DR

This paper investigates how varying quark masses affect the phase structure of two-flavor QCD, highlighting the complexities in relating lattice results to perturbative schemes and implications for the strong CP problem.

Contribution

It analyzes the quark mass dependence of the QCD phase diagram, emphasizing non-universality and scheme dependence in non-degenerate quark masses.

Findings

Regions of first and second order transitions identified.

Non-perturbative effects depend on quark mass ratios and scheme.

Challenges in matching lattice and perturbative results discussed.

Abstract

I explore the rich phase diagram of two-flavor QCD as a function of the quark masses. The theory involves three parameters, including one that is CP violating. As the masses vary, regions of both first and second order transitions are expected. For non-degenerate quarks, non-perturbative effects cease to be universal, leaving individual quark mass ratios with a renormalization scheme dependence. This raises complications in matching lattice results with perturbative schemes and demonstrates the tautology of attacking the strong CP problem via a vanishing up quark mass.