Paul B. Mackenzie

Massive fermions in lattice gauge theory

This paper presents a formulation of lattice fermions applicable to all quark masses, large and small. We incorporate interactions from previous light-fermion and heavy-fermion methods, and thus ensure a smooth connection to these limiting cases. The couplings in improved actions are obtained for arbitrary fermion mass m{sub q}, without expansions around small- or large-mass limits. We treat both the action and external currents. By interpreting on-shell improvement criteria through the lattice theory{close_quote}s Hamiltonian, one finds that cutoff artifacts factorize into the form b{sub n}(m{sub q}a)[{bold p}a]{sup s{sub n}} where {bold p} is a momentum characteristic of the system under study, s{sub n} is related to the dimension of the nth interaction, and b{sub n}(m{sub q}a) is a bounded function, numerically always of order 1 or less. In heavy-quark systems {bold p} is typically rather smaller than the fermion mass m{sub q}. Therefore, artifacts of order (m{sub q}a){sup s} do not arise, even when m{sub q}a{approx_gt}1. An important by-product of our analysis is an interpretation of the Wilson and Sheikholeslami-Wohlert actions applied to nonrelativistic fermions. {copyright} {ital 1997} {ital The American Physical Society}

B- and D-meson decay constants from three-flavor lattice QCD

We calculate the leptonic decay constants ofB (s) andD (s) mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge congurations which include the eects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ms=10) and at three lattice spacings (a 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f B+ = 196:9(8:9) MeV, fBs = 242:0(9:5) MeV, f D+ = 218:9(11:3) MeV, fDs = 260:1(10:8) MeV, and the SU(3) avor-breaking ratios fBs =fB = 1:229(26) and fDs =fD = 1:188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.

Semileptonic decays of d mesons in three-flavor lattice QCD.

We present the first three-flavor lattice QCD calculations for D-->pilnu and D-->Klnu semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC Collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1/8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at q(2)=0 are f(D-->pi)(+)(0)=0.64(3)(6) and f(D-->K)(+)(0)=0.73(3)(7), where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the Cabibbo-Kobayashi-Maskawa matrix elements |V(cd)|=0.239(10)(24)(20) and |V(cs)|=0.969(39)(94)(24), where the last errors are from experimental uncertainties.

B →d ν form factors at nonzero recoil and |Vcb | from 2+1 -flavor lattice QCD

We present the first unquenched lattice-QCD calculation of the hadronic form factors for the exclusive decay

Semileptonic D→π/K and B→π/D decays in 2+1 flavor lattice QCD

\overline{B}\ensuremath{\rightarrow}D\ensuremath{\ell}\overline{\ensuremath{\nu}}

Constrained curve fitting

at nonzero recoil. We carry out numerical simulations on 14 ensembles of gauge-field configurations generated with

Charmed-meson decay constants in three-flavor lattice QCD

2+1

B→πlν semileptonic form factor from three-flavor lattice QCD: A model-independent determination of |Vub|

flavors of asqtad-improved staggered sea quarks. The ensembles encompass a wide range of lattice spacings (approximately 0.045 to 0.12 fm) and ratios of light (up and down) to strange sea-quark masses ranging from 0.05 to 0.4. For the

B(s)0-mixing matrix elements from lattice QCD for the Standard Model and beyond

b

Lattice QCD on small computers

and