Chiral spin symmetry and the QCD phase diagram

Abstract

Lattice QCD simulations with chirally symmetric quarks have recently established approximate $$SU(2)_{CS}$$ S U ( 2 ) CS and $$SU(2N_F)$$ S U ( 2 N F ) symmetries of the quantum effective action in a temperature range above the chiral crossover $$T_\textrm{ch}$$ T ch , in which color-electric interactions between quarks dominate the dynamics. We show that such an intermediate temperature range between the chirally broken and plasma regimes is fully consistent with published screening mass spectra, which demonstrate the breakdown of thermal perturbation theory at the crossover between the partonic and the chiral spin symmetric regime at $$T_s\sim (2-3)T_\textrm{ch}$$ T s ∼ ( 2 - 3 ) T ch . From the known behavior of screening masses with baryon chemical potential, we deduce qualitatively how this chiral spin symmetric band extends into the QCD phase diagram. In the cold and dense region, we propose parity doubled baryons as possible candidates for chiral spin symmetric matter. This represents a special case of quarkyonic matter with confinement and restored chiral symmetry, and can smoothly transform to quark matter at sufficiently high densities. Finally, we discuss the potential of dilepton spectra to identify such matter forms.

Non-perturbative insights into the spectral properties of QCD at finite temperature

“…1 supports the physical picture that the pion and its excitations are sequentially melted, and that this process happens gradually and at temperatures significantly larger than the effective chiral symmetry restoration scale T pc . This picture is also consistent with the expectations of chiral spin symmetry, which predicts the existence of hadron-like states where chiral symmetry is effectively restored but quarks are still bound [28][29][30], and has been shown to be approximately realised in the temperature range T pc T 3T pc on the same lattice configurations [28,29].…”

On chiral spin symmetry and the QCD phase diagram

“…In the cold and dense regime, baryon parity doublet matter is consistent with chiral spin symmetry, provided it is decoupled from π, σ to leading order, otherwise it is only chirally symmetric. Similarly, quarkyonic matter with a chirally symmetric confined regime [18,19] may also be chiral spin symmetric, as discussed in [20]. This is independent of the question whether or not there is a non-analytic chiral phase transition.…”

QCD thermodynamics: an overview of recent progress

“…This trend is brought [32] as additional evidence, along with previously observed multiplet patterns in Domain Wall simulations for 𝑁 f = 2 for the emergent chiral spin symmetry discussed in Refs. [33,34]. In a scenario with chiral spin symmetry at work there would be three temperature regimes with distinguishable symmetries in QCD with an intermediate, approximately SU(4)-symmetric, one featuring a dominance of color electric quark-gluon interactions before these too get screened at about 3𝑇 𝑐 and the usual chiral symmetry gets recovered via a crossover.…”