We describe two calculations involving P-wave mesons made of Wilson quarks: the strong coupling constant $alpha_s$ in the presence of two flavors of light dynamical fermions and the mass and decay constant of the $a_1$ meson.
We present preliminary results for light, strange and charmed pseudoscalar meson physics from simulations using four flavors of dynamical quarks with the highly improved staggered quark (HISQ) action. These simulations include lattice spacings rangin
g from 0.15 to 0.06 fm, and sea-quark masses both above and at their physical value. The major results are charm meson decay constants f_D, f_{D_s} and f_{D_s}/f_D and ratios of quark masses. This talk will focus on our procedures for finding the decay constants on each ensemble, the continuum extrapolation, and estimates of systematic error.
The Banks-Casher relation links the spectral density of the Dirac operator with the existence of a chiral condensate and spontaneous breaking of chiral symmetry. This relation receives corrections from a finite value of the quark mass, a finite space
-time volume and, if evaluated on a discrete lattice, from the finite value of the lattice spacing a. We present a status report of a determination of these corrections for Wilson quarks.
We determine the light meson spectrum in QCD in the presence of background magnetic fields using quenched Wilson fermions. Our continuum extrapolated results indicate a monotonous reduction of the connected neutral pion mass as the magnetic field gro
ws. The vector meson mass is found to remain nonzero, a finding relevant for the conjectured $rho$-meson condensation at strong magnetic fields. The continuum extrapolation was facilitated by adding a novel magnetic field-dependent improvement term to the additive quark mass renormalization. Without this term, sizable lattice artifacts that would deceptively indicate an unphysical rise of the connected neutral pion mass for strong magnetic fields are present. We also investigate the impact of these lattice artifacts on further observables like magnetic polarizabilities and discuss the magnetic field-induced mixing between $rho$-mesons and pions. We also derive Ward-Takashi identities for QCD+QED both in the continuum formulation and for (order $a$-improved) Wilson fermions.
We present our latest results for the excitations of static-light mesons on both quenched and unquenched lattices, where the light quarks are simulated using the chirally improved (CI) lattice Dirac operator.
The excited isovector meson spectrum is explored using two chirally improved dynamical quarks. Seven ensembles, with pion masses down to approx 250 MeV are discussed and used for extrapolations to the physical point. Strange mesons are investigated u
sing partially quenched s-quarks. Using the variational method, we extract excited states in several channels and most of the results are in good agreement with experiment.