110 research outputs found
B Physics on the Lattice: , , , , mixing, \fb and all that
We present a short review of our most recent high statistics lattice
determinations in the HQET of the following important parameters in B physics:
the B--meson binding energy, and the kinetic energy of the
b quark in the B meson, , which due to the presence of power
divergences require a non--perturbative renormalization to be defined; the
running mass of the b quark,
; the -- mass splitting, whose
value in the HQET is determined by the matrix element of the chromo--magnetic
operator between B meson states, ; the B parameter of the
-- mixing, , and the decay constant of the B meson,
. All these quantities have been computed using a sample of gauge
field configurations on a lattice at . For
and , we obtain our
estimates by combining results from three independent lattice simulations at
, and on the same volume.Comment: 3 latex pages, uses espcrc2.sty (included). Talk presented at
LATTICE96(heavy quarks
Results from a Non-Perturbative Renormalization of Lattice Operators
We propose a general renormalization method, which avoids completely the use
of lattice perturbation theory. We present the results from its numerical
applications to two-fermion operators on a lattice, at
.Comment: 3 pages postscript file. Contribution to Lattice '9
A Numerical Study of Partially Twisted Boundary Conditions
We investigate the use of partially twisted boundary conditions in a lattice
simulation with two degenerate flavours of improved Wilson sea quarks. The use
of twisted boundary conditions on a cubic volume (L^3) gives access to
components of hadronic momenta other than integer multiples of 2*pi/L. Partial
twisting avoids the need for new gluon configurations for every choice of
momentum, while, as recently demonstrated, keeping the finite-volume errors
exponentially small for the physical quantities investigated in this letter. In
this study we focus on the spectrum of pseudo scalar and vector mesons, on
their leptonic decay constants and on Z_P, the matrix element of the pseudo
scalar density between the pseudo scalar meson and the vacuum. The results
confirm the momentum shift imposed by these boundary conditions and in addition
demonstrate that they do not introduce any appreciable noise. We therefore
advocate the use of partially twisted boundary conditions in applications where
good momentum resolution is necessary.Comment: 10 pages, 3 figure
Non-Perturbative Renormalisation of Composite Operators
It is shown that the renormalisation constants of two quark operators can be
accurately determined (to a precision of a few per-cent using 18 gluon
configurations) using Chiral Ward identities. A method for computing
renormalisation constants of generic composite operators without the use of
lattice perturbation theory is proposed.Comment: 3 pages, uuencoded compressed postscript file, to appear in the
Proceedings of the International Symposium on Lattice Field Theory, Dallas,
Texas, 12-17 October 1993, Southampton Preprint 93/94-0
Computation of the b-quark Mass with Perturbative Matching at the Next-to-Next-to-Leading Order
We compute the two-loop term in the perturbation series for the quark-mass in
the lattice Heavy Quark Effective Theory. This is an ingredient in the matching
factor required to obtain the -quark mass from lattice simulations of the
HQET. Combining our calculations with numerical results from the APE
collaboration, we find, at two-loop order, GeV. It was expected that
the two-loop term would have a significant effect and this is indeed what we
find. Depending on the choice of "reasonable" coupling constant in the one-loop
estimates the result for can change by several hundred MeV when the
two-loop terms are included.Comment: 24 Pages, 1 Figur
Finite-Volume Two-Pion Amplitudes in the I=0 Channel
We perform a calculation in one-loop chiral perturbation theory of the
two-pion matrix elements and correlation functions of an I=0 scalar operator,
in finite and infinite volumes for both full and quenched QCD. We show that
major difficulties arise in the quenched theory due to the lack of unitarity.
Similar problems are expected for quenched lattice calculations of amplitudes with . Our results raise the important question
of whether it is consistent to study amplitudes beyond leading
order in chiral perturbation theory in quenched or partially quenched QCD.Comment: Version to appear on Phys. Lett. B, with only very minor and
stylistic change
A High Statistics Lattice Calculation of The B-meson Binding Energy
We present a high statistics lattice calculation of the B--meson binding
energy of the heavy--quark inside the pseudoscalar
B--meson. Our numerical results have been obtained from several independent
numerical simulations at , and , and using, for the meson
correlators, the results obtained by the APE group at the same values of
. Our best estimate, obtained by combining results at different values
of , is MeV. For the
running mass, we obtain
GeV, in reasonable
agreement with previous determinations. The systematic error is the truncation
of the perturbative series in the matching condition of the relevant operator
of the Heavy Quark Effective Theory.Comment: Latex, 13 pages, 1 figure appended in uuencoded gzip.tar.fil
Future Perspectives in Lattice Field Theory
I review some of the contributions which lattice simulations are likely to
make during the next five years or so to the development of our understanding
of particle physics. Particular emphasis is given to the evaluation of
non-perturbative QCD effects in experimentally measurable amplitudes, and the
corresponding extraction of fundamental parameters.Comment: 10 Pages, Latex, 3 .eps figures and espcrc2.sty files. To be
published in the proceedings of the XVIIth International Symposium on Lattice
Field Theory, \textit{Lattice 99}, Pisa, Italy, June~28th - July~3rd 199
Renormalization of the Lattice HQET Isgur-Wise Function
We compute the perturbative renormalization factors required to match to the
continuum Isgur-Wise function, calculated using lattice Heavy Quark Effective
Theory. The velocity, mass, wavefunction and current renormalizations are
calculated for both the forward difference and backward difference actions for
a variety of velocities. Subtleties are clarified regarding tadpole
improvement, regulating divergences, and variations of techniques used in these
renormalizations.Comment: 28 pages, 0 figures, LaTeX. Final version accepted for publication in
Phys. Rev. D. (Minor changes.
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