Convergence Rate and Locality of Improved Overlap Fermions

TL;DR

This paper introduces improved overlap fermions for QCD that significantly accelerate convergence and enhance locality and rotational symmetry, reducing computational overhead while maintaining accuracy.

Contribution

The authors develop a new class of Ginsparg-Wilson fermions using an approximately chiral Dirac operator, improving convergence and locality over standard methods.

Findings

Convergence accelerated by a factor of 5

Locality exponent doubled, indicating better correlation decay

Approximate rotation invariance significantly improved

Abstract

We construct new Ginsparg-Wilson fermions for QCD by inserting an approximately chiral Dirac operator - which involves ingredients of a perfect action - into the overlap formula. This accelerates the convergence of the overlap Dirac operator by a factor of 5 compared to the standard construction, which inserts the Wilson fermion as a point of departure. Taking into account the effort for treating the improved fermion, we are left with an total computational overhead of about a factor 3. This remaining factor is likely to be compensated by other virtues; here we show that the level of locality is clearly improved, so that the exponent of the correlation decay is doubled. We also show that approximate rotation invariance is drastically improved, but a careful scaling test has to be postponed.