159 research outputs found
1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-
Using a known result by Falk et al. for the 1/m_b^2 correction to the
dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we
calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry
in this decay. Employing an up-to-date range of values for the non-perturbative
parameter \lambda_1, we find that the correction is much smaller than it should
have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear
in Physical Review D. The complete postscript file is also available from URL
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g
Next--to--Leading Order Corrections to Meson Masses in the Heavy Quark Effective Theory
We use the QCD sum rule approach to calculate the splitting between vector
and pseudoscalar mesons containing one light and one heavy quark, and the
kinetic energy of the heavy quark. Our result for the splitting induced by the
chromomagnetic interaction agrees to the experimental data on charm and beauty
mesons. For the matrix element of the kinetic energy operator, we obtain the
value .Comment: 33 ps., PS figures included, requires REVTEX.3 and psfig,
TUM-T31-42/93/R (additional contribution to kinetic energy taken into
account, marginal changes in the results
Exclusive Radiative B-Decays in the Light-Cone QCD Sum Rule Approach
We carry out a detailed study of exclusive radiative rare -decays in the
framework of the QCD sum rules on the light cone, which combines the
traditional QCD sum rule technique with the description of final state vector
mesons in terms of the light-cone wave functions of increasing twist. The
decays considered are: and the corresponding decays of the mesons, and . Based on our estimate of the transition
form factor F_1^{B \to K^*\pg}(0) =0.32\pm0.05, we find for the branching
ratio , which is in
agreement with the observed value measured by the CLEO collaboration. We
present detailed estimates for the ratios of the radiative decay form factors,
which are then used to predict the rates for the exclusive radiative B-decays
listed above. This in principle allows the extraction of the CKM matrix element
from the penguin-dominated CKM-suppressed radiative decays when they
are measured. We give a detailed discussion of the dependence of the form
factors on the -quark mass and on the momentum transfer, as well as their
interrelation with the CKM-suppressed semileptonic decay form factors in , which we also calculate in our approach.Comment: 32 pages, 10 uuencoded figures, LaTeX, preprint CERN-TH 7118/9
Vector meson dominance and the rho meson
We discuss the properties of vector mesons, in particular the rho^0, in the
context of the Hidden Local Symmetry (HLS) model. This provides a unified
framework to study several aspects of the low energy QCD sector. Firstly, we
show that in the HLS model the physical photon is massless, without requiring
off field diagonalization. We then demonstrate the equivalence of HLS and the
two existing representations of vector meson dominance, VMD1 and VMD2, at both
tree level and one loop order. Finally the S matrix pole position is shown to
provide a model and process independent means of specifying the rho mass and
width, in contrast to the real axis prescription currently used in the Particle
Data Group tables.Comment: 18 pages, REVTE
Progress in Classical and Quantum Variational Principles
We review the development and practical uses of a generalized Maupertuis
least action principle in classical mechanics, in which the action is varied
under the constraint of fixed mean energy for the trial trajectory. The
original Maupertuis (Euler-Lagrange) principle constrains the energy at every
point along the trajectory. The generalized Maupertuis principle is equivalent
to Hamilton's principle. Reciprocal principles are also derived for both the
generalized Maupertuis and the Hamilton principles. The Reciprocal Maupertuis
Principle is the classical limit of Schr\"{o}dinger's variational principle of
wave mechanics, and is also very useful to solve practical problems in both
classical and semiclassical mechanics, in complete analogy with the quantum
Rayleigh-Ritz method. Classical, semiclassical and quantum variational
calculations are carried out for a number of systems, and the results are
compared. Pedagogical as well as research problems are used as examples, which
include nonconservative as well as relativistic systems
Multiple Scattering Expansion of the Self-Energy at Finite Temperature
An often used rule that the thermal correction to the self-energy is the
thermal phase-space times the forward scattering amplitude from target
particles is shown to be the leading term in an exact multiple scattering
expansion. Starting from imaginary-time finite-temperature field theory, a
rigorous expansion for the retarded self-energy is derived. The relationship to
the thermodynamic potential is briefly discussed.Comment: 33 pages. Uses ReVTeX and epsf. 8 figure
Anomalous enhancements of low-energy fusion rates in plasmas: the role of ion momentum distributions and inhomogeneous screening
Non-resonant fusion cross-sections significantly higher than corresponding
theoretical predictions are observed in low-energy experiments with deuterated
matrix target. Models based on thermal effects, electron screening, or
quantum-effect dispersion relations have been proposed to explain these
anomalous results: none of them appears to satisfactory reproduce the
experiments. Velocity distributions are fundamental for the reaction rates and
deviations from the Maxwellian limit could play a central role in explaining
the enhancement. We examine two effects: an increase of the tail of the target
Deuteron momentum distribution due to the Galitskii-Yakimets quantum
uncertainty effect, which broadens the energy-momentum relation; and spatial
fluctuations of the Debye-H\"{u}ckel radius leading to an effective increase of
electron screening. Either effect leads to larger reaction rates especially
large at energies below a few keV, reducing the discrepancy between
observations and theoretical expectations.Comment: 6 pages, 3 figure
Hadronic Correlation Functions in the Interacting Instanton Liquid
We study hadronic correlation functions in the interacting instanton liquid
model, both at zero and nonzero temperature . At zero we investigate the
dependence of the correlators on the instanton ensemble, in particular the
effect of the fermionic determinant. We demonstrate that quark-induced
correlations between instantons are important, especially in the repulsive
and -meson channels. We also calculate a large number of
mesonic and baryonic correlation functions as a function of temperature. We
find three different types of behavior as . The vector channels
show a gradual melting of the resonance contribution and
approach free quark behavior near the chiral phase transition. The light
pseudoscalars and scalars , as well as the nucleon show stable
resonance contributions, probably even surviving above . Correlation
functions in the heavy scalar channels are enhanced as .Comment: 34 pages, Revtex, 7 postscript figure
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