Non-perturbative determination of the $N_f=2+1$ QCD sphaleron rate

TL;DR

This paper presents the first non-perturbative lattice QCD calculation of the strong sphaleron rate for Nf=2+1 flavors at physical parameters, covering temperatures from 200 to 600 MeV, crucial for understanding QCD topological transitions.

Contribution

It introduces a novel non-perturbative lattice approach using a modified Backus-Gilbert method to determine the sphaleron rate at the physical point.

Findings

First reliable non-perturbative computation of the sphaleron rate in Nf=2+1 QCD.

Temperature range covered from 200 MeV to 600 MeV.

Results relevant for heavy-ion collisions and early-Universe cosmology.

Abstract

The strong sphaleron rate, i.e., the rate of real time QCD topological transitions, is a key phenomenological quantity, playing a fundamental role in several physical contexts. In heavy-ion collisions, a non-vanishing rate can lead to the so-called Chiral Magnetic Effect. In early-Universe cosmology, instead, it can be related to the rate of thermal production of QCD axions. In this talk, we present the first reliable fully non-perturbative computation of the strong sphaleron rate in $N_f=2+1$ QCD at the physical point by means of lattice simulations, in a range of temperatures going from 200 MeV to 600 MeV. Our strategy is based on the inversion of lattice correlators via a recently-proposed modified version of the Backus-Gilbert method.