# Topology (and axion's properties) from lattice QCD with a dynamical charm

## TL;DR

This study uses lattice QCD simulations with four dynamical flavors to analyze topological properties relevant to the QCD axion as a Dark Matter candidate, especially near the QCD transition temperature.

## Contribution

It provides new lattice QCD results on topological susceptibility and charge distribution with dynamical charm quarks, supporting the dilute instanton gas approximation at high temperatures.

## Key findings

- Topological susceptibility shows a power-law decay consistent with DIGA at high T.
- Near the transition temperature, the effective exponent approaches DIGA predictions.
- Results help constrain the axion dark matter window based on topological properties.

## Abstract

We present results on QCD with four dynamical flavors in the temperature range $0.9 \lesssim T/T_c \lesssim 2$. We have performed lattice simulations with Wilson fermions at maximal twist and measured the topological charge with gluonic and fermionic methods. The topological charge distribution is studied by means of its cumulants, which encode relevant properties of the QCD axion, a plausible Dark Matter candidate. The topological susceptibility measured with the fermionic method exhibits a power-law decay for $T/T_c \gtrsim 2$, with an exponent close to the one predicted by the Dilute Instanton Gas Approximation (DIGA). Close to $T_c$ the temperature dependent effective exponent approaches the DIGA result from above, in agreement with recent analytic calculations. These results constrain the axion window, once an assumption on the fraction of axions contributing to Dark Matter is made.