Simulation of QCD with N f = 2 + 1 flavors of non-perturbatively improved Wilson fermions

Abstract

Journal of High Energy Physics 2015.2 (2015): 043 reproduced by permission of Scuola Internazionale Superiore di Studi Avanzati (SISSA)We describe a new set of gauge configurations generated within the CLS effort. These ensembles have N f = 2 + 1 flavors of non-perturbatively improved Wilson fermions in the sea with the L ̈uscher-Weisz action used for the gluons. Open boundary conditions in time are used to address the problem of topological freezing at small lattice spacings and twisted-mass reweighting for improved stability of the simulations. We give the bare parameters at which the ensembles have been generated and how these parameters have been chosen. Details of the algorithmic setup and its performance are presented as well as measurements of the pion and kaon masses alongside the scale parameter t 0M.B., P.K., T.K. and S.S. are supported by the Deutsche Forschungsgemeinschaft (DFG) in the SFB/TR 09 “Computational Particle Physics”. G.P.E. acknowledges partial support by the MIUR-PRIN contract 20093BMNNPR and G.H. acknowledges support by the the Spanish MINECO through the Ram ́on y Cajal Programme and through the project FPA2012-31686 and by the Centro de excelencia Severo Ochoa Program SEV- 2012-0249. G.H. and H.H. acknowledge the support from the DFG in the SFB 1044. M.P. acknowledges partial support by the MIUR-PRIN contract 2010YJ2NYW and by the INFN SUMA project. E.E.S, J.S., and W.S. are supported by the SFB/TRR-55 “Hadron Physics from Lattice QCD” by the DFG. E.E.S. also acknowledges support from the EU grant PIRG07-GA-2010-26836

Non-perturbative improvement and renormalization of the axial current in N_f=3 lattice QCD

“…Similarly large cutoff effects at this β were also observed for this action in [24]. However, at smaller lattice spacings the results for both definitions of Z A are in good agreement within their errors.…”

The determination of α s by the ALPHA collaboration

“…Our computation of hadronic scales is based on the CLS large volume simulations with two degenerate light quarks, m u = m d and one additional strange quark [25]. 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 .…”

Non-perturbative determination of improvement coefficients using coordinate space correlators in Nf=2+1 lattice QCD

“…Therefore, errors from neglecting the associated radiative corrections will be completely insignificant in comparison to our statistical errors. However, we also corrected for the leading non-perturbative effect that is proportional to 4 . This correction relies not only on the validity of the Gell-Mann-Oakes-Renner relation in our regime of quark masses but there exist also perturbative corrections to the Wilson coefficient, that we have neglected.…”

“…We add 20% of the subtracted 4 terms to our systematic error budget to reflect this uncertainty. In order to discriminate whether the effect seen in the pseudoscalar channel is due to particularly large radiative corrections, lattice artefacts or interference from different higher order terms, a perturbative calculation of the 4 Wilson coefficient is ongoing.…”

“…In Table II we summarize the ensembles employed and how many measurements were taken; for more details see Refs. [4,15]. Typically we perform 50 to 100 measurements, that are separated by 20 to 40 molecular dynamics units (MDUs) in the Markov Monte-Carlo chain.…”