35 research outputs found
Hybrid Quarkonia with High Statistics from NRQCD
We have studied the O(mv^6) effects in NRQCD on the spectrum of heavy
quarkonia and compare our results for different lattices (quenched and
dynamical). We also report on an investigation into hybrid states within the
framework of NRQCD. This suggests that the lowest lying hybrid is around the
B^* \bar B threshold and 3 standard deviations above the B \bar B.Comment: 3 pages, LaTeX2e, 4 figures, uses styles [espcrc2, epsf], talk
presented at Lattice 9
NRQCD on an anisotropic lattice
We present preliminary results for the Upsilon spectrum on an anisotropic
lattice using the improved O(mv^6) NRQCD Hamiltonian. We find accurate results
can be obtained in moderate computer times and that they agree with earlier
results on an isotropic lattice.Comment: 3 pages, LATEX2e, talk presented at LATTICE '98 by R.R. Horgan, uses
styles[espcrc2,epsfig
QCD Pressure and the Trace Anomaly
Exact relations between the QCD thermal pressure and the trace anomaly are
derived. These are used, first, to prove the equivalence of the thermodynamic
and the hydrodynamic pressure in equilibrium in the presence of the trace
anomaly, closing a gap in previous arguments. Second, in the temporal axial
gauge a formula is derived which expresses the thermal pressure in terms of a
Dyson-resummed two-point function. This overcomes the infrared problems
encountered in the conventional perturbation-theory approach.Comment: 9 pages plain te
Improved Langevin Methods for Spin Systems
We investigate methods for variance reduction and the elimination of
systematic error in a Fourier accelerated Langevin scheme for general spin
models. We present results for the model in
two-dimensions that are consistent wit h those from multi-grid methods. We
argue that the timing for the Langevin method makes it comparable to multi-grid
for a given level of error.Comment: 16, DAMTP-92-7
Semileptonic B Decays from an NRQCD/D234 Action
Semileptonic B decays are studied on quenched anisotropic lattices using
Symanzik improved glue, NRQCD heavy quark and D234 light quark actions. We
employ constrained fits to extract ground state contributions to two- and
three-point correlators. Results for the B --> pi, l nubar decay form factors
are compared with previous lattice results. We find that our systematic errors
(excluding quenching errors) are dominated by chiral extrapolation
uncertainties.Comment: Lattice2002(Heavy quark physics
Lattice perturbation theory for gluonic and fermionic actions
We calculate the two loop Landau mean links and the one loop renormalisation
of the anisotropy for Wilson and improved SU(3) gauge actions, using twisted
boundary conditions as a gauge invariant infrared regulator. We show these
accurately describe simulated results, and outline a method for generating
Feynman rules for general lattice field theories, in a form suitable for
efficient numerical calculation of perturbative loop diagrams.Comment: 6 pages of LaTeX. Two posters at Lattice2002(improve) combine
Radial Excited States for Heavy Quark Systems in NRQCD
Following the Non-Relativistic QCD approach we use a gauge invariant smearing
method with factorization to measure the excitation energies for a heavy
system on a lattice at . The results come
from averaging over an ensemble of 60 QCD configurations. In order to enhance
the signal from each configuration we use wall sources for quark propagators.
The quark Hamiltonian contains only the simplest non-relativistic kinetic
energy term. The results are listed for a range of bare quark masses. The mass
splittings are insensitive to this variable though there are a slight trends
with increasing quark mass. For an appropriate choice of UV cut-off
(Gev) the mass spectrum compares reasonably well with the
experimental values for the spin-averaged energy gaps of the system.
We also present results for the and waves for the lowest bare quark
mass. The results are consistent with degeneracy between the two types of
wave. This encourages the idea that even with our simple quark Hamiltonian the
departure from rotational invariance is not great.Comment: 12 page
Non-Relativistic QCD for Heavy Quark Systems
We employ a nonrelativistic version of QCD (NRQCD) to study heavy
quark-antiquark bound states in the lowest approximation without fine
structure. We use gluon configurations on a 16^3 by 48 lattice at beta=6.2 from
the UKQCD collaboration. For quark masses in the vicinity of the b we obtain
bound state masses for S, P and both types of D wave. We also detect signals
for two types of hybrids (quark,antiquark,gluon states). The results are
sufficiently accurate to confirm that the values of the D wave mass from both
lattice D waves coincide indicating that the cubical invariance of the lattice
is restored to full rotational invariance at large distance.
Our results also show that the S-P splitting is indeed insensitive to
variations in the bare quark mass from Ma=1.0 to Ma=1.9.Comment: 13 pages, DAMTP-92-7
Eliminating Infrared Divergences in the Pressure
The pressure of a system in thermal equilibrium is expressed as a mass
integral over a sum of thermal propagators. This allows a Dyson resummation and
is used to demonstrate that potential infrared divergences are rendered
harmless.Comment: 6 pages plain tex, including figures embedded using eps
Automatically generating Feynman rules for improved lattice field theories
Deriving the Feynman rules for lattice perturbation theory from actions and
operators is complicated, especially when improvement terms are present. This
physically important task is, however, suitable for automation. We describe a
flexible algorithm for generating Feynman rules for a wide range of lattice
field theories including gluons, relativistic fermions and heavy quarks. We
also present an efficient implementation of this in a freely available,
multi-platform programming language (\python), optimised to deal with a wide
class of lattice field theories