Four Flavor Finite Temperature Phase Transition with HYP Action: Where is the First Order Phase Transition Line?

TL;DR

This study investigates the finite temperature phase transition of four-flavor staggered fermions with HYP fat links, showing that increased smoothness weakens the first order transition and may eliminate it within accessible parameters.

Contribution

The paper introduces a new algorithm for simulating fermions with HYP fat links and demonstrates how smearing affects the phase transition behavior.

Findings

First order transition weakens with increased smearing.

No transition observed with the smoothest HYP action at accessible temperatures.

Improved flavor symmetry likely influences the phase diagram.

Abstract

We study the finite temperature phase transition of four flavor staggered fermions with hypercubic fat link actions on N_t=4 and N_t=6 temporal lattices. Our fat links are constructed with hypercubic blocking (HYP) and therefore are very compact. We present a new algorithm for simulating fermions coupled to HYP fat links. The algorithm has a simple form based on the standard overrelaxation and heatbath updatings for the pure gauge action. We observe that as we increase the smoothness of the gauge fields by changing the parameters of the blocking the very pronounced first order phase transition of the thin link action becomes weaker and moves to physically uninteresting values of the gauge coupling. With our smoothest HYP action we do not find any indication of a phase transition in the accessible temperature range on the N_t=4 or 6 lattices even at quark masses close to the physical light quark mass. We argue that the observed difference in the phase diagram is due to the improved flavor symmetry of the smeared link actions.