673 research outputs found
Lattice Charge Overlap II: Aspects of Charged Pion Polarizability
Formulas are developed for use in lattice studies of charged hadron
polarizabilities. In particular, the valence quark different-flavor component
of the charged pion polarizability is examined on a lattice
at using Wilson fermions. Using the elastic limit results of Part I
of this series, it is concluded that this represents a small negative component
of the full charged polarizabilty.Comment: RevTeX file with one ps figur
Radiative Corrections to and Decays
We reexamine radiative corrections to and decays. We
perform a matching calculation, including vector and axial vector resonances as
explicit degrees of freedom in the long distance part. By considering the
dependence on the matching scale and on the hadronic parameters, and by
comparing with model independent estimates, we scrutinize the model dependence
of the results. For the pseudoscalar meson decay constants, we extract the
values f_pi = (92.1 \pm 0.3) MeV and f_K = (112.4 \pm 0.9) MeV. For the ratios
R_pi and R_K of the electronic and muonic decay modes, we predict R_pi =
(1.2354 \pm 0.0002) 10^{-4} and R_K = (2.472 \pm 0.001) 10^{-5}.Comment: 8 pages, Latex, uses epsfig. Revised version: Major changes in the
presentaion, but no changes in the results. To appear in Phys. Lett.
Leading-twist light cone distribution amplitudes for p-wave heavy quarkonium states
In this paper, a study of light-cone distribution amplitudes for p-wave heavy
quarkonium states are presented. Within the light-front framework, the leading
twist light-cone distribution amplitudes, and their relevant decay constants,
have some simple relations. These relations can be further simplified when the
non-relativistic limit and the wave function as a function of relative momentum
|\vec\kappa| are taken into consideration. In addition, the \kappa_\perp
integrations in the equations of LCDAs and \xi-moments can be completed
analytically when the Gaussian-type wave function is considered. After fixing
the parameters that appear in the wave function, the curves and the
corresponding decay constants of the LCDAs are plotted and calculated for the
charmonium and bottomonium states. The first three \xi-moments of the LCDAs are
estimated and are consistent with those of other theoretical approaches.Comment: 25 pages, 2 figures, some details and one reference added; version to
appear in JHE
Hard pion bremsstrahlung in the Coulomb region
Hard high-energy pion-nucleus bremsstrahlung, ,
is studied in the Coulomb region, i.e. the small-angle region where the nuclear
scattering is dominated by the Coulomb interaction. Special attention is
focussed on the possibility of measuring the pion polarizability in such
reactions. We study the sensitivity to the structure of the underlying the
pion-Compton amplitude through a model with , , and a_1
exchanges. It is found that the effective energy in the virtual pion-Compton
scattering is often so large that the threshold approximation does not apply.Comment: 18 pages, 5 figure
Semileptonic and Exclusive Rare B Decays
The exclusive rare decay B \ra K^\ast \gamma takes place in a region of
maximum recoil, , posing a problem for nonrelativistic quark models
which are usually thought to be most reliable at zero recoil. The
Bauer--Stech--Wirbel (BSW) model, formulated in the infinite--momentum--frame
(IMF) formalism, is designed to work at . We show in this model that the
ratio relating the decay B \ra K^\ast \gamma and the --spectrum of the
semileptonic decay B\ra \rho e {\bar \nu}, becomes independent of the wave
function in the SU(3) flavor symmetry limit. We show that this feature is also
true in relativistic quark models formulated in the IMF or light--cone
formalism, if the quark is infinitely heavy. In fact, these relativistic
models, which have a different spin structure from the BSW case, reduce to the
BSW model in the heavy --quark limit. A direct measurement of the
--spectrum of the semileptonic decay can therefore provide accurate
information for the exclusive rare decay.Comment: 13 pages, Latex, no figure, UTPT--94--0
The interplay of soft and hard contributions in the electromagnetic pion form factor
We consider various relativistic models for the valence Fock-state wave
function of the pion. These models are obtained from simple instant-form wave
functions by applying a Melosh rotation to the spin part and by imposing
physical constraints on the parameters. We discuss how the soft and the hard
(perturbative) parts of the electromagnetic form factor are affected by the
choice of the model and by the Melosh rotation.Comment: 3 pages, 2 eps-figures, uses espcrc2.st
Light Front Theory Of Nuclear Matter
A relativistic light front formulation of nuclear dynamics is applied to
infinite nuclear matter. A hadronic meson-baryon Lagrangian, consistent with
chiral symmetry, leads to a nuclear eigenvalue problem which is solved,
including nucleon-nucleon (NN) correlations, in the one-boson-exchange
approximation for the NN potential. The nuclear matter saturation properties
are reasonably well reproduced, with a compression modulus of 180 MeV. We find
that there are about 0.05 excess pions per nucleon.Comment: 6 pages, Revtex, one figure; version resubmitted to Phys. Lett.
N=4 central charge superspace at work for supergravity coupled to an arbitrary number of abelian vector multiplets
We present the description in central charge superspace of N=4 supergravity
with antisymmetric tensor coupled to an arbitrary number of abelian vector
multiplets. All the gauge vectors of the coupled system are treated on the same
footing as gauge fields corresponding to translations along additional bosonic
coordinates. It is the geometry of the antisymmetric tensor which singles out
which combinations of these vectors belong to the supergravity multiplet and
which are the additional coupled ones. Moreover, basic properties of
Chapline-Manton coupling mechanism, as well as the SO(6,n)/SO(6)*SO(n) sigma
model of the Yang-Mills scalars are found as arising from superspace geometry.Comment: 18 page
Thermophysical characteristics of radioactive graphite - Water vapor system
The article considers thermophysical characteristics of radioactive graphite - water vapor system in temperature range 373-3273K. The research was made by thermodynamic modeling method using TERRA software. We determined 4 temperature intervals in which changes of thermophysical characteristics of radioactive graphite - water vapor system occur. © 2017 The Authors, published by EDP Sciences
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