Universality crossover between chiral random matrix ensembles and twisted SU(2) lattice Dirac spectra

TL;DR

This paper investigates the universality crossover in Dirac spectra of QCD-like theories under perturbations, using random matrix theory and lattice simulations to accurately determine physical constants.

Contribution

It introduces a numerical approach to evaluate eigenvalue distributions in chiral random matrix ensembles and confirms universality through lattice model comparisons.

Findings

Excellent fit of spectral data with a one-parameter model

Precise determination of the pion decay constant F

Validation of universality across different lattice models

Abstract

Motivated by the statistical fluctuation of Dirac spectrum of QCD-like theories subjected to (pseudo)reality-violating perturbations and in the epsilon-regime, we compute the smallest eigenvalue distribution and the level spacing distribution of chiral and non-chiral parametric random matrix ensembles of Dyson-Mehta-Pandey type. To this end we employ the Nystrom method to numerically evaluate the Fredholm Pfaffian of the integral kernel for the chG(O,S)E-chGUE and G(O,S)E-GUE crossover. We confirm the validity and universality of our results by comparing them with several lattice models, namely fundamental and adjoint staggered Dirac spectra of SU(2) quenched lattice gauge theory under the twisted boundary condition (imaginary chemical potential) or perturbed by phase noise. Both in the zero-virtuality region and in the spectral bulk, excellent one-parameter fitting is achieved already on a small 4^4 lattice. Anticipated scaling of the fitting parameter with the twisting phase, mean level spacing, and the system size allows for precise determination of the pion decay (diffusion) constant F in the low-energy effective Lagrangian.