71 research outputs found
A High-Statistics Lattice Calculation of and in the meson
We present a high-statistics lattice calculation of the kinetic energy
of the heavy quark inside the -meson and of the
chromo-magnetic term , related to the -- mass splitting,
performed in the HQET. Our results have been obtained from a numerical
simulation based on 600 gauge field configurations generated at , on
a lattice volume and using, for the meson correlators, the
results obtained with the SW-Clover improved lattice action for the
light quarks. For the kinetic energy we found ~GeV, which
is interesting for phenomenological applications. We also find GeV, corresponding to GeV, which is about one half of the experimental value. The origin
of the discrepancy with the experimental number needs to be clarified.Comment: 26 pages, latex, 5 figure
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.
Spectator Effects in Inclusive Decays of Beauty Hadrons
We present a model-independent study of spectator effects, which are
responsible for the lifetime differences between beauty hadrons. These effects
can be parametrized in terms of hadronic matrix elements of four four-quark
operators. For mesons, the coefficients of the non-factorizable operators
turn out to be much larger than those of the factorizable ones, limiting
considerably the usefulness of the vacuum insertion approximation.
Non-factorizable contributions to the lifetime ratio
could naturally be of order 10--20%, and not even the sign of these
contributions can be predicted at present. In the case of the
baryon, heavy-quark symmetry is used to reduce the number of independent matrix
elements from four to two. In order to explain the large deviation from unity
in the experimental result for , it is necessary
that these baryon matrix elements be much larger than those estimated in quark
models. We have also reexamined the theoretical predictions for the
semileptonic branching ratio of mesons and charm counting, finding that,
given the present theoretical and experimental uncertainties, there is no
significant discrepancy with experiment.Comment: 32 pages, 5 postscript figures included, revised version to appear in
Nuclear Physics
Phenomenological constraints on SUSY SU(5) GUTs with non-universal gaugino masses
We study phenomenological aspects of supersymmetric SU(5) grand unified
theories with non-universal gaugino masses. For large tan beta, we investigate
constraints from the requirement of successful electroweak symmetry breaking,
the positivity of stau mass squared and the b to s gamma decay rate. In the
allowed region, the nature of the lightest supersymmetric particle is
determined. Examples of mass spectra are given. We also calculate loop
corrections to the bottom mass due to superpartners.Comment: 10 pages, 2 figures (8 eps files), uses REVTeX. Replaced to match the
version to be published in PRD: minor corrections and addition
Exclusive Decays of Beauty Hadrons
The principal difficulty in deducing weak interaction properties from
experimental measurements of -decays lies in controlling the strong
interaction effects. In this talk I review the status of theoretical
calculations of the amplitudes for exclusive leptonic and semileptonic decays,
in the latter case with special emphasis on the extraction of the and
matrix elements.Comment: Invited lecture presented at the workshop "Beauty '96", Rome, June
17-21 1996. 19 pages, latex, axodraw.sty, 7 figure
Plastic Flow in Two-Dimensional Solids
A time-dependent Ginzburg-Landau model of plastic deformation in
two-dimensional solids is presented. The fundamental dynamic variables are the
displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t.
Damping is assumed to arise from the shear viscosity in the momentum equation.
The elastic energy density is a periodic function of the shear and tetragonal
strains, which enables formation of slips at large strains. In this work we
neglect defects such as vacancies, interstitials, or grain boundaries. The
simplest slip consists of two edge dislocations with opposite Burgers vectors.
The formation energy of a slip is minimized if its orientation is parallel or
perpendicular to the flow in simple shear deformation and if it makes angles of
with respect to the stretched direction in uniaxial stretching.
High-density dislocations produced in plastic flow do not disappear even if
the flow is stopped. Thus large applied strains give rise to metastable,
structurally disordered states. We divide the elastic energy into an elastic
part due to affine deformation and a defect part. The latter represents degree
of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at
http://stat.scphys.kyoto-u.ac.jp/index-e.htm
A Phenomenological Analysis of Heavy Hadron Lifetimes
A phenomenological analysis of lifetimes of bottom and charmed hadrons within
the framework of the heavy quark expansion is performed. The baryon matrix
element is evaluated using the bag model and the nonrelativistic quark model.
We find that bottom-baryon lifetimes follow the pattern
.
However, neither the lifetime ratio nor the
absolute decay rates of the baryon and mesons can be explained.
One way of solving both difficulties is to allow the presence of linear
corrections by scaling the inclusive nonleptonic width with the fifth power of
the hadron mass rather than the heavy quark mass . The hierarchy
of bottom baryon lifetimes is dramatically modified to
: The
longest-lived among bottom baryons in the OPE prescription now
becomes shortest-lived. The replacement of by in nonleptonic
widths is natural and justified in the PQCD-based factorization approach
formulated in terms of hadron-level kinematics. For inclusive charmed baryon
decays, we argue that since the heavy quark expansion does not converge, local
duality cannot be tested in this case. We show that while the ansatz of
substituting the heavy quark mass by the hadron mass provides a much better
description of the charmed-baryon lifetime {\it ratios}, it appears unnatural
and unpredictive for describing the {\it absolute} inclusive decay rates of
charmed baryons, contrary to the bottom case.Comment: 35 pages, to appear in Phys. Rev. The CDF result on the lifetime
ratio of Lambda_b and B_d is discusse
Rare Charm Decays in the Standard Model and Beyond
We perform a comprehensive study of a number of rare charm decays,
incorporating the first evaluation of the QCD corrections to the short distance
contributions, as well as examining the long range effects. For processes
mediated by the transitions, we show that sensitivity to
short distance physics exists in kinematic regions away from the vector meson
resonances that dominate the total rate. In particular, we find that
and are sensitive to non-universal
soft-breaking effects in the Minimal Supersymmetric Standard Model with
R-parity conservation. We separately study the sensitivity of these modes to
R-parity violating effects and derive new bounds on R-parity violating
couplings. We also obtain predictions for these decays within extensions of the
Standard Model, including extensions of the Higgs, gauge and fermion sectors,
as well as models of dynamical electroweak symmetry breaking.Comment: 45 pages, typos fixed, discussions adde
Gaugino Mass Nonuniversality and Dark Matter in SUGRA, Strings and D Brane Models
The effects of nonuniversality of gaugino masses on dark matter are examined
within supersymmetric grand unification, and in string and D brane models with
R parity invariance. In SU(5) unified models nonuniversality in the gaugino
sector can be generated via the gauge kinetic energy function which may depend
on the 24, 75 and 200 dimensional Higgs representations. We also consider
string models which allow for nonuniversality of gaugino masses and D brane
models where nonuniversality arises from embeddings of the Standard Model gauge
group on five branes and nine branes. It is found that with gaugino mass
nonuniversality the range of the LSP mass can be extended much beyond the range
allowed in the universal SUGRA case, up to about 600 GeV even without
coannihilation effects in some regions of the parameter space. The effects of
coannihilation are not considered and inclusion of these effects may further
increase the allowed neutralino mass range. Similarly with the inclusion of
gaugino mass nonuniversality, the neutralino-proton () cross-section
can increase by as much as a factor of 10 in some of regions of the parameter
space. An analysis of the uncertainties in the quark density content of the
nucleon is given and their effects on cross-section are discussed.
The predictions of our analysis including nonuniversality is compared with the
current limits from dark matter detectors and implications for future dark
matter searches are discussed.Comment: Revised version, 23 pages, Latex, and 7 figure
First lattice calculation of the B-meson binding and kinetic energies
We present the first lattice calculation of the B-meson binding energy and of the kinetic energy -lambda(1)/2m(Q) of the heavy-quark inside the pseudoscalar B-meson. This calculation has required the non-perturbative subtraction of the power divergences present in matrix elements of the Lagrangian operator and of the kinetic energy operator , The non-perturbative renormalisation of the relevant operators has been implemented by imposing suitable renormalisation conditions on quark matrix elements, in the Landau gauge. Our numerical results have been obtained from several independent numerical simulations at beta = 6.0 and 6.2, and using, for the meson correlators, the results obtained by the APE group at the same values of beta. Our best estimate, obtained by combining results at different values of beta, is = 190(-30)(+50) MeV. For the running mass, we obtain () = 4.17 +/- 0.06 GeV, in reasonable agreement with previous determinations. From a subset of 36 configurations, we were only able to establish a loose upper bound on the 6-quark kinetic energy in a B-meson, lambda(1) = [B\\B]/(2M(B)) < 1 GeV2. This shows that a much larger statistical sample is needed to determine this important parameter
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