Dirac spectral density in Nf=2+1 QCD at T=230 MeV

We compute the renormalized Dirac spectral density in Nf=2+1 QCD at physical quark masses, temperature T=230 MeV, and system size Ls=3.4 fm. To that end, we perform a pointwise continuum limit of the staggered density in lattice QCD with staggered quarks. We find, for the first time, that a clear infrared structure (IR peak) emerges in the density of the Dirac operator describing dynamical quarks. We also provide numerical evidence that a component of this peak, which becomes dominant in the thermodynamic limit, is due to a nontrivial accumulation of near-zero modes. Features of this structure are consistent with those previously attributed to the recently proposed IR phase of thermal QCD. Our results (i) provide the only complete first-principles evidence that these IR features exist and are physical, (ii) improve the upper bound for IR phase transition temperature TIR so that the new window is 200<230 MeV, and (iii) are consistent with the nonrestoration of anomalous UA(1) symmetry (chiral limit) below T=230 MeV.