A test of first order scaling in Nf=2 QCD

TL;DR

This study tests the universality class of Nf=2 QCD using lattice simulations, finding evidence for a first order transition rather than the expected O(4) universality class.

Contribution

It introduces a new analysis strategy to distinguish between universality classes in lattice QCD and provides evidence supporting a first order transition in Nf=2 QCD.

Findings

No agreement with O(4) universality class in the tested mass range.

Evidence of a first order transition from scaling behavior.

Chiral susceptibilities show deviations from expected scaling.

Abstract

We complete our analysis of Nf=2 QCD based on the lattice staggered fermion formulation. Using a series of Monte Carlo simulations at fixed (amq*Ls^yh) one is able to test the universality class with given critical exponent yh. This strategy has been used to test the O(4) universality class and it has been presented at the previous Lattice conferences. No agreement was found with simulations in the mass range amq=[0.01335,0.15] using lattices with Ls=16 up to 32 and Lt=4. With the same strategy, we now investigate the possibility of a first order transition using a new set of Monte Carlo data corresponding to yh=3 in the same mass and volume range as the one used for O(4). A substantial agreement is observed both in the specific heat scaling and in the scaling of the chiral condensate, while the chiral susceptibilities still presents visible deviation from scaling in the mass range explored.