Dynamical fat link fermions

TL;DR

This paper introduces an alternative projection method for fat link fermions in lattice QCD that enables the use of standard Hybrid Monte Carlo algorithms for dynamical simulations.

Contribution

It proposes a new projection technique that is differentiable, allowing efficient dynamical fermion simulations with fat link actions.

Findings

Enables the use of standard HMC algorithms with fat link fermions.

Provides a differentiable projection method for reunitarisation.

Facilitates more efficient lattice QCD simulations.

Abstract

The use of APE smearing or other blocking techniques in fermion actions can provide many advantages. There are many variants of these fat link actions in lattice QCD currently, such as FLIC fermions. Frequently, fat link actions make use of the APE blocking technique in combination with a projection of the blocked links back into the special unitary group. This reunitarisation is often performed using an iterative maximisation of a gauge invariant measure. This technique is not differentiable with respect to the gauge field and thus prevents the use of standard Hybrid Monte Carlo simulation algorithms. The use of an alternative projection technique circumvents this difficulty and allows the simulation of dynamical fat link fermions with standard HMC and its variants.