Simulation of an ensemble of Nf = 2 + 1 + 1 twisted mass cloverimproved fermions at physical quark masses

Jacob Finkenrath,Giancarlo Rossi,Simone Bacchio,Constantia Alexandrou,Panagiotis Charalambous,Bartosz Kostrzewa,Carsten Urbach,Karl Jansen,Roberto Frezzotti,Petros Dimopoulos

doi:10.1051/epjconf/201817502003

Abstract

We present a general strategy aimed at generating Nf = 2+1+1 configurations with quarks at their physical mass using maximally twisted mass fermions to ensure automatic O(a) improvement, in the presence of a clover term tuned to reduce the charged to neutral pion mass difference. The target system, for the moment, is a lattice of size 643 × 128 with a lattice spacing a ~ 0:08 fm. We show preliminary results on the pion and kaon mass and decay constants.

Highlights

During the last decade, lattice QCD simulations with light quarks having physical masses on large enough volumes have become feasible owing to improvements in lattice actions and numerical algorithms as well as due to steadily increasing computational power
The tuning procedure is quite complicated as a number of parameters have to be simultaneously set at appropriate values
We use the Hybrid Monte Carlo (HMC) algorithms [12] with Hasenbusch mass-preconditioning [13] for the light quark sector and the rational HMC [14] for the heavy quark sector

Summary

Introduction

Lattice QCD simulations with light quarks having physical masses on large enough volumes have become feasible owing to improvements in lattice actions and numerical algorithms as well as due to steadily increasing computational power. We illustrate a strategy aimed at generating N f = 2 + 1 + 1 configurations with quarks at the physical mass using maximally twisted fermions to ensure automatic O(a) improvement This bonus does not come without a price, as the twisted regularization breaks isospin leading to an undesired (negative) neutral pion to charged mass splitting. Conserved Axial Current (PCAC) mass vanishes, which is equivalent to tuning the bare mass parameter κ(m) to its critical value [4, 5] In this case, the renormalized light quark mass is at maximal twist and related to m = μ /ZP with ZP the pseudoscalar renormalization constant.

Tuning towards physical quark masses

Stable algorithms

Observables

Conclusion