37 research outputs found
The heavy quark's self energy from moving NRQCD on the lattice
We present a calculation of the heavy quark's self energy in moving NRQCD to
one-loop in perturbation theory. Results for the energy shift and external
momentum renormalisation are discussed and compared with non-perturbative
results. We show that the momentum renormalisation is small, which is the
result of a remnant of re-parameterisation invariance on the lattice.Comment: Talk given at Lattice2004(heavy), Fermilab, June 21-26, 200
Exploratory lattice QCD study of the rare kaon decay
In Ref [1] we have presented the results of an exploratory lattice QCD
computation of the long-distance contribution to the
decay amplitude. In the present paper we describe the details of this
calculation, which includes the implementation of a number of novel techniques.
The decay amplitude is dominated by short-distance
contributions which can be computed in perturbation theory with the only
required non-perturbative input being the relatively well-known form factors of
semileptonic kaon decays. The long-distance contributions, which are the target
of this work, are expected to be of O(5%) in the branching ratio. Our study
demonstrates the feasibility of lattice QCD computations of the
decay amplitude, and in particular of the
long-distance component. Though this calculation is performed on a small
lattice () and at unphysical pion, kaon and charm quark masses,
MeV, MeV and m_c^{\overline{\mathrm{MS}}}(\mbox{2
GeV})=863 MeV, the techniques presented in this work can readily be applied to
a future realistic calculation.Comment: 74 pages, 12 figure
Perturbative and Nonperturbative Renormalization in Lattice QCD
We investigate the perturbative and nonperturbative renormalization of
composite operators in lattice QCD restricting ourselves to operators that are
bilinear in the quark fields (quark-antiquark operators). These include
operators which are relevant to the calculation of moments of hadronic
structure functions. The nonperturbative computations are based on Monte Carlo
simulations with two flavors of clover fermions and utilize the
Rome-Southampton method also known as the RI-MOM scheme. We compare the results
of this approach with various estimates from lattice perturbation theory, in
particular with recent two-loop calculations.Comment: 54 pages, 15 figures; v2: several clarifications and additions, two
more figures, results unchanged; v3: typos in eqs.(C33) and (E2) corrected,
results unchange
The pion's electromagnetic form factor at small momentum transfer in full lattice QCD
We compute the electromagnetic form factor of a "pion" with mass m_pi=330MeV
at low values of Q^2\equiv -q^2, where q is the momentum transfer. The
computations are performed in a lattice simulation using an ensemble of the
RBC/UKQCD collaboration's gauge configurations with Domain Wall Fermions and
the Iwasaki gauge action with an inverse lattice spacing of 1.73(3)GeV. In
order to be able to reach low momentum transfers we use partially twisted
boundary conditions using the techniques we have developed and tested earlier.
For the pion of mass 330MeV we find a charge radius given by
_{330MeV}=0.354(31)fm^2 which, using NLO SU(2) chiral perturbation
theory, extrapolates to a value of =0.418(31)fm^2 for a physical pion,
in agreement with the experimentally determined result. We confirm that there
is a significant reduction in computational cost when using propagators
computed from a single time-slice stochastic source compared to using those
with a point source; for m_pi=330MeV and volume (2.74fm)^3 we find the
reduction is approximately a factor of 12.Comment: 20 pages, 3 figure