540 research outputs found
Relation between Light Cone Distribution Amplitudes and Shape Function in B mesons
The Bakamjian-Thomas relativistic quark model provides a Poincar\'e
representation of bound states with a fixed number of constituents and, in the
heavy quark limit, form factors of currents satisfy covariance and Isgur-Wise
scaling. We compute the Light Cone Distribution Amplitudes of mesons
as well as the Shape Function , that enters
in the decay , that are also covariant in this class of
models. The LCDA and the SF are related through the quark model wave function.
The former satisfy, in the limit of vanishing constituent light quark mass, the
integral relation given by QCD in the valence sector of Fock space. Using a
gaussian wave function, the obtained is identical to the so-called
Roman Shape Function. From the parameters for the latter that fit the spectrum we predict the behaviour of . We
discuss the important role played by the constituent light quark mass. In
particular, although for vanishing light quark mass, a
non-vanishing mass implies the unfamiliar result . Moreover,
we incorporate the short distance behaviour of QCD to ,
which has sizeable effects at large . We obtain the values for the
parameters GeV and
GeV. We compare with other theoretical approaches and illustrate the
great variety of models found in the literature for the functions ; hence the necessity of imposing further constraints as in the
present paper. We briefly review also the different phenomena that are
sensitive to the LCDA.Comment: 6 figure
Relativistic quantum theories and neutrino oscillations
Neutrino oscillations are examined under the broad requirements of
Poincar\'e-invariant scattering theory in an S-matrix formulation.
This approach can be consistently applied to theories with either field or
particle degrees of freedom. The goal of this paper is to use this general
framework to identify all of the unique physical properties of this problem
that lead to a simple oscillation formula. We discuss what is in principle
observable, and how many factors that are important in principle end up being
negligible in practice.Comment: 21 pages, no figure
Axial-vector mesons in a relativistic point-form approach
The Poincare invariant coupled-channel formalism for two-particle systems
interacting via one-particle exchange, which has been developed and applied to
vector mesons in Ref. [1] is applied to axial vector mesons. We thereby extend
the previous study of a dynamical treatment of the Goldstone-boson exchange by
comparison with the commonly used instantaneous approximation to the case of
orbital angular momentum l=1. Effects in the mass shifts show more variations
than for the vector-meson case. Results for the decay widths are sizable, but
comparison with sparse experimental data is inconclusive.Comment: 4 pages, 1 figur
Rotational covariance and light-front current matrix elements
Light-front current matrix elements for elastic scattering from hadrons with
spin~1 or greater must satisfy a nontrivial constraint associated with the
requirement of rotational covariance for the current operator. Using a model
meson as a prototype for hadronic quark models, this constraint and its
implications are studied at both low and high momentum transfers. In the
kinematic region appropriate for asymptotic QCD, helicity rules, together with
the rotational covariance condition, yield an additional relation between the
light-front current matrix elements.Comment: 16 pages, [no number
Mimesis stories: composing new nature music for the shakuhachi
Nature is a widespread theme in much new music for the shakuhachi (Japanese bamboo flute). This article explores the significance of such music within the contemporary shakuhachi scene, as the instrument travels internationally and so becomes rooted in landscapes outside Japan, taking on the voices of new creatures and natural phenomena. The article tells the stories of five compositions and one arrangement by non-Japanese composers, first to credit composers’ varied and personal responses to this common concern and, second, to discern broad, culturally syncretic traditions of nature mimesis and other, more abstract, ideas about the naturalness of sounds and creative processes (which I call musical naturalism). Setting these personal stories and longer histories side by side reveals that composition creates composers (as much as the other way around). Thus it hints at much broader terrain: the refashioning of human nature at the confluence between cosmopolitan cultural circulations and contemporary encounters with the more-than-human world
The Balian-Br\'ezin Method in Relativistic Quantum Mechanics
The method suggested by Balian and Br\'ezin for treating angular momentum
reduction in the Faddeev equations is shown to be applicable to the
relativistic three-body problem.Comment: 14 pages in LaTe
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
Deuteron tensor polarization component T_20(Q^2) as a crucial test for deuteron wave functions
The deuteron tensor polarization component T_20(Q^2) is calculated by
relativistic Hamiltonian dynamics approach. It is shown that in the range of
momentum transfers available in to-day experiments, relativistic effects, meson
exchange currents and the choice of nucleon electromagnetic form factors almost
do not influence the value of T_20(Q^2). At the same time, this value depends
strongly on the actual form of the deuteron wave function, that is on the model
of NN-interaction in deuteron. So the existing data for T_20(Q^2) provide a
crucial test for deuteron wave functions.Comment: 11 pages, 3 figure
Solving the inhomogeneous Bethe-Salpeter equation
We develop an advanced method of solving homogeneous and inhomogeneous
Bethe-Salpeter equations by using the expansion over the complete set of
4-dimensional spherical harmonics. We solve Bethe-Salpeter equations for bound
and scattering states of scalar and spinor particles for the case of one meson
exchange kernels. Phase shifts calculated for the scalar model are in agreement
with the previously published results. We discuss possible manifestations of
separability for one meson exchange interaction kernels.Comment: 9 pages, 11 eps-figures. Talk presented by S. S. Semikh at XVII
International Baldin Seminar on High Energy Physics Problems "Relativistic
Nuclear Physics and Quantum Chromodynamics", September 27 - October 2, 2004,
Dubna, Russia; to appear in the proceedings of this conferenc
Feynman Graphs and Generalized Eikonal Approach to High Energy Knock-Out Processes
The cross section of hard semi-exclusive reactions for fixed
missing energy and momentum is calculated within the eikonal approximation.
Relativistic dynamics and kinematics of high energy processes are unambiguously
accounted for by using the analysis of appropriate Feynman diagrams. A
significant dependence of the final state interactions on the missing energy is
found, which is important for interpretation of forthcoming color transparency
experiments. A new, more stringent kinematic restriction on the region where
the contribution of short-range nucleon correlations is enhanced in
semi-exclusive knock-out processes is derived. It is also demonstrated that the
use of light-cone variables leads to a considerable simplification of the
description of high-energy knock-out reactions.Comment: 24 pages, LaTex, two Latex and two ps figures, uses FEYNMAN.tex and
psfig.sty. Revisied version to appear in Phys. Rev.
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