Eigenvalue spectra of QCD and the fate of $U_A(1)$ breaking towards the chiral limit

Abstract

The finite temperature phase diagram of QCD with two massless quark flavors is not yet understood because of the subtle effects of anomalous $U_A(1)$ symmetry. In this work we address this issue by studying the fate of the anomalous $U_A(1)$ symmetry in $2+1$ flavor QCD just above the chiral crossover transition temperature $T_c$, lowering the light quark mass towards the chiral limit along line of constant physical strange quark mass. We use the gauge configurations generated using the Highly Improved Staggered Quark (HISQ) discretization on lattice volumes $32^3\times 8$ and $56^3\times 8$ to study the renormalized eigenvalue spectrum of QCD with valence overlap Dirac operator. We have implemented new numerical techniques that have allowed us to measure about $100$-$200$ eigenvalues of the gauge ensembles with light quark masses $\gtrsim 0.6$ MeV. From a detailed analysis of the dependence of the renormalized eigenvalue spectrum and $U_A(1)$ breaking observables on the light quark mass, our study suggests $U_A(1)$ is broken at $T\gtrsim T_c$ even when the chiral limit is approached.

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Cited by in corpus (19)

• Chiral spin symmetry and the QCD phase diagram
• QCD phase transitions in the light quark chiral limit
• The chiral phase transition and the axial anomaly
• Localization of Dirac Fermions in Finite-Temperature Gauge Theory
• Second order chiral phase transition in three flavor quantum chromodynamics?
• Chiral spin symmetry and hot/dense QCD
• Anderson Metal-to-Critical Transition in QCD
• Eigenvalues of the QCD Dirac matrix with improved staggered quarks in the continuum limit
• Localised Dirac eigenmodes, chiral symmetry breaking, and Goldstone's theorem at finite temperature
• Deconfinement transition and localization of Dirac modes in finite-temperature ${\mathbb{Z}}_3$ gauge theory on the lattice
• Localisation of Dirac modes in gauge theories and Goldstone's theorem at finite temperature
• Thermal behavior of effective U_A(1) anomaly couplings in reflection of higher topological sectors
• QCD Anderson transition with overlap valence quarks on a twisted-mass sea
• $U_A(1)$ symmetry breaking quark interactions from vacuum polarization
• $U_A(1)$ symmetry restoration at high baryon density
• Understanding the approach to thermalization from the eigenspectrum of non-Abelian gauge theories
• Universal microscopic spectrum of the unquenched QCD Dirac operator at finite temperature
• Probing the chiral and $U(1)$ axial symmetry restoration via meson susceptibilities in holographic QCD
• Backreaction of mesonic fluctuations on the axial anomaly at finite temperature