Tuning the strange quark mass in lattice simulations

Abstract

QCD lattice simulations with 2 + 1 flavours typically start at rather large up-down and strange quark masses and extrapolate first the strange quark mass to its physical value and then the up-down quark mass. An alternative method of tuning the quark masses is discussed here in which the singlet quark mass is kept fixed, which ensures that the kaon always has mass less than the physical kaon mass. It can also take into account the different renormalisations (for singlet and non-singlet quark masses) occurring for non-chirally invariant lattice fermions and so allows a smooth extrapolation to the physical quark masses. This procedure enables a wide range of quark masses to be probed, including the case with a heavy updown quark mass and light strange quark mass. Results show the correct order for the baryon octet and decuplet spectrum and an extrapolation to the physical pion mass gives mass values to within a few percent of their experimental values.2

Low-lying baryon masses using Nf=2 twisted mass clover-improved fermions directly at the physical pion mass

“…In addition, we compare with QCDSF-UKQCD results from Ref. [66], using N f = 2 + 1 SLiNC configurations. The Budapest-Marseille-Wuppertal (BMW) collaboration have also obtained the strange baryon spectrum using tree level improved 6-step stout smeared N f = 2 + 1 clover fermions and a tree level Symanzik improved gauge action [67] at a = 0.065, 0.085 and 0.125 fm.…”

The determination of α s by the ALPHA collaboration

“…In these simulations the trace, m u + m d + m s , of the quark mass matrix is held constant [26] while varying m u = m d in approaching the physical point defined by physical values for m π / f πK , m K / f πK . Along this trajectory in the quark mass plane the linear combination…”

Disconnected contributions to the spin of the nucleon

“…The lattice spacing a ¼ 0.074ð2Þ fm is set using a number of singlet quantities [29][30][31][32]. The clover action used comprises the tree-level Symanzik improved gluon action together with a stout smeared fermion action, modified for the implementation of the FH method [24].…”