Isoscalar mesons upon unbreaking of chiral symmetry

TL;DR

This study uses lattice QCD simulations to show that removing low-lying Dirac eigenmodes leads to chiral symmetry restoration and degeneracy of meson states, revealing an underlying SU(4) symmetry in the meson spectrum.

Contribution

It demonstrates that truncating low-lying Dirac eigenmodes results in chiral symmetry restoration and reveals an emergent SU(4) symmetry among mesons in lattice QCD.

Findings

Disconnected correlators vanish after mode removal.

All J=0 correlators with different quantum numbers become identical.

J=1 meson ground states show clear exponential decay and degeneracy.

Abstract

In a dynamical lattice simulation with the overlap Dirac operator and $N_f=2$ mass degenerate quarks we study all possible $J=0$ and $J=1$ correlators upon exclusion of the low lying "quasi-zero" modes from the valence quark propagators. After subtraction of a small amount of such Dirac eigenmodes all disconnected contributions vanish and all possible point-to-point $J=0$ correlators with different quantum numbers become identical, signaling a restoration of the $SU(2)_L \times SU(2)_R \times U(1)_A$. The original ground state of the $\pi$ meson does not survive this truncation, however. In contrast, in the $I=0$ and $I=1$ channels for the $J=1$ correlators the ground states have a very clean exponential decay. All possible chiral multiplets for the $J=1$ mesons become degenerate, indicating a restoration of an $SU(4)$ symmetry of the dynamical QCD-like string.