# Chiral Susceptibilities in noncompact QED: a new determination of the $\gamma$ exponent and the critical couplings

## TL;DR

This paper measures susceptibilities in noncompact QED4 on various lattices, determining the critical exponent gamma as 1 and confirming critical couplings with high precision, challenging some theoretical predictions.

## Contribution

The study provides a new, precise determination of the gamma exponent and critical couplings in noncompact QED4 using susceptibility measurements in the chiral limit.

## Key findings

- Gamma exponent is 1, independent of flavor symmetry.
- Critical couplings match previous fermion effective action results.
- Results contradict certain scalar mean field theory predictions.

## Abstract

We report the results of a measurement of susceptibilities in noncompact $QED_4$ in $8^4, 10^4$ and $12^4$ lattices. Due to the potentialities of the $MFA$ approach, we have done simulations in the chiral limit which are therefore free from arbitrary mass extrapolations. Our results in the Coulomb phase show unambiguously that the susceptibility critical exponent $\gamma=1$ independently of the flavour symmetry group. The critical couplings extracted from these calculations are in perfect agreement with previous determinations based on the fermion effective action and plaquette energy, and outside the predictions of a logarithmically improved scalar mean field theory by eight standard deviations.