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

Abstract

We present results on QCD with four dynamical flavors in the temperature range 0.9 T/T c 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 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.

The dark-matter axion mass

“…sanyi et al at lower temperatures [36][37][38][39][40][41], although no group has reproduced these higher temperatures and even below 600 MeV there are some results which appear discrepant [42,43]. Therefore we will explore other n values but consider values near n = 7.5 to be likely correct.…”

Estimating $$\chi _\mathrm {top}$$ lattice artifacts from flowed SU(2) calorons

“…In this case, besides the now rather well-determined value of the topological susceptibility in vacuum [8], we also need the topological susceptibility in the temperature range 3 T c -7 T c [9,10], since this is the temperature range where a cosmological axion density would be established. The exploration of topological susceptibility at high temperatures within QCD has recently become the topic of intense investigation [11][12][13][14][15][16][17][18]. (For a recent review of the axion see Ref.…”

Axions, instantons, and the lattice

“…Recently there have been a number of papers reporting lattice calculations of χ(T ) at temperatures above the critical temperature, both in pure gauge theory/quenched approximations [9,10,8] and in QCD [11,12,13,7,14,15,16]. In some cases, discrepancies are found at high temperatures compared with the dilute instanton gas prediction.…”