$N_f=1+2$ mass dependence of the topological susceptibility

TL;DR

This paper investigates how the topological susceptibility in QCD depends on quark masses, using lattice simulations with different fermion masses to explore implications for the strong CP problem.

Contribution

It provides new lattice QCD results on the mass dependence of topological susceptibility, especially in the context of the $N_f=1+2$ flavor setup, highlighting non-perturbative effects.

Findings

Preliminary results for four different fermion masses.

Enhanced sensitivity to non-perturbative effects with large down quark mass.

Insights into the $m_u=0$ ambiguity in the strong CP problem.

Abstract

A massless up quark has long been proposed as a solution to the strong CP problem. While this solution is sometimes thought to have been excluded, it is actually still ill-defined. In this work, we study the mass dependence of the physical observable $\chi_t$, the topological susceptibility. Assigning an unphysically large value to the down mass allows to be more sensitive to the non-perturbative effects behind the $m_u=0$ ambiguity. Preliminary results are presented for four masses of clover fermions.