Brian Pendleton

Hybrid Monte Carlo

We present a new method for the numerical simulation of lattice field theory. A hybrid (molecular dynamics/Langevin) algorithm is used to guide a Monte Carlo simulation. There are no discretization errors even for large step sizes. The method is especially efficient for systems such as quantum chromodynamics which contain fermionic degrees of freedom. Detailed results are presented for four-dimensional compact quantum electrodynamics including the dynamical effects of electrons.

Physical results from 2+1 flavor domain wall QCD and SU(2) chiral perturbation theory

We have simulated QCD using 2+1 flavors of domain wall quarks on a (2.74fm)3 volume with an inverse lattice scale of a?1=1.729(28) GeV. The up and down (light) quarks are degenerate in our calculations and we have used four values for the ratio of light quark masses to the strange (heavy) quark mass in our simulations: 0.217, 0.350, 0.617 and 0.884. We have measured pseudoscalar meson masses and decay constants, the kaon bag parameter BK and vector meson couplings. We have used SU(2) chiral perturbation theory, which assumes only the up and down quark masses are small, and SU(3) chiral perturbation theory to extrapolate to the physical values for the light quark masses. While next-to-leading order formulae from both approaches fit our data for light quarks, we find the higher order corrections for SU(3) very large, making such fits unreliable. We also find that SU(3) does not fit our data when the quark masses are near the physical strange quark mass. Thus, we rely on SU(2) chiral perturbation theory for accurate results. We use the masses of the ? baryon, and the ? and K mesons to set the lattice scale and determine the quark masses. We then find f?=124.1(3.6)stat(6.9)systMeV, fK=149.6(3.6)stat(6.3)systMeV and fK/f?=1.205(0.018)stat(0.062)syst. Using non-perturbative renormalization to relate lattice regularized quark masses to RI-MOM masses, and perturbation theory to relate these to MS¯ we find mMS¯ud(2GeV)=3.72(0.16)stat(0.33)ren(0.18)systMeV and mMS¯s(2GeV)=107.3(4.4)stat(9.7)ren(4.9)systMeV.

Continuum limit physics from 2+1 flavor domain wall QCD

We present physical results obtained from simulations usin g 2+1 flavors of domain wall quarks and the Iwasaki gauge action at two values of the lattice spac ing a, (a−1= 1.73 (3) GeV and a−1= 2.28 (3) GeV). On the coarser lattice, with 24 3×64×16 points (where the 16 corresponds to Ls, the extent of the 5 th dimension inherent in the domain wall fermion (DWF) formula tion

Gauge-invariant smearing and matrix correlators using Wilson fermions at beta =6.2.

We present an investigation of gauge-invariant smearing for Wilson fermions in quenched lattice QCD on a

2 + 1 flavor domain wall QCD on a (2 fm)3 lattice : Light meson spectroscopy with Ls = 16

24^3 \times 48

Neutral-Kaon Mixing from (2 + 1)-Flavor Domain-Wall QCD

lattice at

Acceptances and autocorrelations in hybrid Monte Carlo

\beta = 6.2

Cost of the generalised hybrid Monte Carlo algorithm for free field theory

. We demonstrate a smearing algorithm that allows a substantial improvement in the determination of the baryon spectrum obtained using propagators smeared at both source and sink, at only a small computational cost. We investigate the matrix of correlators constructed from local and smeared operators, and are able to expose excited states of both the mesons and baryons.

Phase diagrams of U(1) lattice Higgs models

We present results for light meson masses and pseudoscalar decay constants from the first of a series of lattice calculations with 2 + 1 dynamical flavors of domain wall fermions and the Iwasaki gauge action. The work reported here was done at a fixed lattice spacing of about 0.12 fm on a 16 3 × 32 lattice, which amounts to a spatial volume of (2 fm) 3 in physical units. The number of sites in the fifth dimension is 16, which gives m res = 0.00308(4) in these simulations. Three values of input light sea quark masses, m sea l ≈ 0.85m s , 0.59m s and 0.33m s were used to allow for extrapolations to the physical light quark limit, while the heavier sea quark mass was fixed to approximately the physical strange quark mass m s . The exact rational hybrid Monte Carlo algorithm was used to evaluate the fractional powers of the fermion determinants in the ensemble generation. We have found that f π = 127(4) MeV, f K = 157(5) MeV and f K /f π = 1.24(2), where the errors are statistical only, which are in good agreement with the experimental values.

Large scale applications of transputers in HEP: The Edinburgh concurrent supercomputer project

We present the first results for neutral-kaon mixing using (2+1)-flavors of domain-wall fermions. A new approach is used to extrapolate to the physical up and down quark masses from our numerical studies with pion masses in the range 240-420 MeV; only SU(2)_{L}xSU(2)_{R} chiral symmetry is assumed and the kaon is not assumed to be light. Our main result is B_{K};{MS[over ]}(2 GeV)=0.524(10)(28) where the first error is statistical and the second incorporates estimates for all systematic errors.