Lattice QCD ensembles with four flavors of highly improved staggered quarks

Abstract

We present results from our simulations of quantum chromodynamics (QCD) with four flavors of quarks: u, d, s, and c. These simulations are performed with a one-loop Symanzik improved gauge action, and the highly improved staggered quark (HISQ) action. We are generating gauge configurations with four values of the lattice spacing ranging from 0.06 fm to 0.15 fm, and three values of the light quark mass, including the value for which the Goldstone pion mass is equal to the physical pion mass. We discuss simulation algorithms, scale setting, taste symmetry breaking, and the autocorrelations of various quantities. We also present results for the topological susceptibility which demonstrate the improvement of the HISQ configurations relative to those generated earlier with the asqtad improved staggered action.

Axion phenomenology and θ-dependence from N f = 2 + 1 lattice QCD

“…For standard discretizations, such properties are recovered only for small enough lattice spacings, so that a careful investigation of the continuum limit becomes essential. Indeed only recently it was possible to measure the dependence of the topological susceptibility on the quark masses to a sufficient accuracy to be compared with the prediction of chiral perturbation theory [23][24][25][26][27].…”

Twisted finite-volume corrections to K l3 decays with partially-quenched and rooted-staggered quarks

“…With the exception of the meson masses and the hairpin couplings, those parameters are originally listed in ref. [18]. The taste splittings shown in table 2 are averages over tastes that are degenerate under the residual SO(4) taste symmetry, which is unbroken at the order to which we are working.…”

“…Taste splittings from refs. [18,39,40] and the r 1 /a in table 1 and hairpin vertices from an unpublished MILC analysis. The correspondence between ensembles here and in table 1 is given by the lattice spacing a since the splittings used are the same for all ensembles with a given lattice spacing.…”

“…From the pion and kaon masses in table 1 we fix the lowest order masses 1 for the neutral particles (pseudo-scalar taste for JHEP03(2017)120 Table 1. Parameters for the HISQ N f = 2 + 1 + 1 MILC ensembles we have used in the numerical results [18]. The numbers not in that reference come from the on-going FNAL/MILC analysis [38].…”

“…We have applied the numerical programs to a set of ensembles from the MILC collaboration's HISQ ensembles [18] to show expected sizes of the corrections. The main conclusions are that the finite-volume corrections are small for present lattices.…”