906 research outputs found
Transition from a relativistic constituent-quark model to the quantum-chromodynamical asymptotics: a quantitative description of the pion electromagnetic form factor at intermediate values of the momentum transfer
We adopt a non-perturbative relativistic constituent-quark model for the
pi-meson electromagnetic form factor, which have successfully predicted
experimental results, and supplement it with the effective momentum-dependent
quark mass to study quantitatively the transition to the perturbative QCD
asymptotics. The required asymptotical behaviour (including both the Q^{-2}
fall-off and the correct coefficient) settles down automatically when the quark
mass is switched off; however, the present experimental data on the form factor
suggest that this cannot happen at the values of the momentum transfer below
~10 GeV^2. The effective constituent-quark mass below this scale acquires
substantial non-perturbative contributions.Comment: 7 pages, RevTex 4.1, 5 figures. V2: a reference added, minor textual
changes, version accepted by Phys. Rev.
Constraining scenarios of the soft/hard transition for the pion electromagnetic form factor with expected data of 12-GeV Jefferson Lab experiments and of the Electron-Ion Collider
It has been shown previously [PRD 88 (2013) 093005, arXiv:1310.1770] that a
non-perturbative relativistic constituent-quark model for the pi-meson
electromagnetic form factor allows for a quantitative description of the
soft/hard transition, resulting in the correct Quantum-Chromodynamical
asymptotics, including normalization, from the low-energy data without further
parameter tuning. This happens universally whenever the constituent-quark mass
is switched off. The energy range where the transition happens is therefore
determined by the quark-mass running at intermediate energies and is not
tightly constrained theoretically. Here we consider possible ways to pin down
this energy range with coming experimental data. We demonstrate that expected
experimental uncertainties of the 12-GeV Jefferson-Lab data are larger than the
span of predictions of the model, so these data might be used for testing the
model but not for determination of the soft/hard transition scale. Contrary,
the projected Electron-Ion Collider will be capable of pinning down the scale.Comment: V2: 11 pages, 3 figures (presentation improved; results unchanged;
matches the PRD accepted version
Hilbert C*-modules from group actions: beyond the finite orbits case
Continuous actions of topological groups on compact Hausdorff spaces are
investigated which induce almost periodic functions in the corresponding
commutative C*-algebra. The unique invariant mean on the group resulting from
averaging allows to derive a C*-valued inner product and a Hilbert C*-module
which serve as an environment to describe characteristics of the group action.
For uniformly continuous, Lyapunov stable actions the derived invariant mean
is continuous on for any element , and the
induced C*-valued inner product corresponds to a conditional expectation from
onto the fixed point algebra of the action defined by averaging on
orbits. In the case of selfduality of the Hilbert C*-module all orbits are
shown to have the same cardinality. Stable actions on compact metric spaces
give rise to C*-reflexive Hilbert C*-modules. The same is true if the
cardinality of finite orbits is uniformly bounded and the number of closures of
infinite orbits is finite. A number of examples illustrate typical situations
appearing beyond the classified cases.Comment: 18 page
Instant-Form Approach to Two-Body Systems
We present a relativistic treatment of the problem of soft electromagnetic
structure by the modified instant form of relativistic Hamiltonian dynamics.
Our approach uses relativistic parametrization and so picks out the
relativistic invariant quantities on each stage of the calculation. The
electromagnetic current matrix element satisfies the current conservation law
automatically. We use relativistic modified impulse approximation. It is
constructed in relativistic invariant way. For composite systems (including the
spin 1 case) the approach guarantees the uniqueness of the solution and it does
not use such concepts as "good" and "bad" current components. The approach
describes correctly the spin Wigner rotation and so gives the correct (QCD)
asymptotic.Comment: 9 pages, latex, no figures Talk presented by V.T. at the Workshop on
Relativisic Approaches to Few-Body Systems, Groningen, July 21, 199
A reflexivity criterion for Hilbert C*-modules over commutative C*-algebras
A C*-algebra is C*-reflexive if any countably generated Hilbert C*-module
over is C*-reflexive, i.e. the second dual module coincides with
. We show that a commutative C*-algebra is C*-reflexive if and only if
for any sequence of disjoint non-zero C*-subalgebras, the canonical
inclusion doesn't extend to an inclusion of .Comment: 9 page
Relativistic Effects in Two-Body Systems: pi- and K-mesons and Deuteron
The electromagnetic form factors of and mesons and deuteron are
calculated in modified impulse approximation using instant form of relativistic
Hamiltonian dynamics. The different model wave functions are used. Meson wave
function parameters are fixed by fitting the mean square radius of meson. The
internal quark structure is taken into account through electromagnetic quark
form factor and quark anomalous magnetic moments. Results of our calculations
of electroweak structure of pion and kaon and electromagnetic deuteron
properties agree well with the available experimental data. The meson form
factors asymptotics at large momentum transfer is the same as in perturbative
QCD. Some predictions about CEBAF experiments are given.Comment: 11 pages, latex, 7 .ps figures. Poster presented by V.T. at the 15th
International Conference on Few-Body Problems in Physics, Groningen, July
22-26, 199
Comment on New Results for the Charged Pion Electromagnetic Form Factor
In the paper nucl-ex/0010009 by The Jefferson Lab F_pi Collaboration the new
results for the charged pion electromagnetic form factor are presented. The
approach given in our paper hep-ph/9811318, "On a possible estimation of the
constituent--quark parameters from Jefferson Lab experiments on the pion form
factor" makes it possible to estimate the mass of constituent quark from such
kind of experiment. Now this estimation gives M=0.21 GeV.Comment: 2 page
Electroweak properties of light mesons in relativistic hamiltonian dynamics
The calculation of lepton decay constants and electromagnetic form factors of
pion and kaon is performed in the framework of relativistic hamiltonian
dynamics. The different model wave function is used. Wave function parameters
are fixed from fit of mean square radius of meson. The internal quark structure
is taken into account by electromagnetic quark form factor and quark anomalous
magnetic moment. The pion and kaon form factors depend only weakly on model
wave function. Strong dependence of these values on quark anomalous magnetic
moment is obtained in the transfer momentum region of CEBAF experiments.Comment: 6 pages, LATEX, 1 postscript figure. Talk at XIII International
Seminar on High Energy Physics Problems, 2-7 September, 1996, Dubna, Russi
Relativistic Instant--Form Approach to the Structure of Two-Body Composite Systems. II. Nonzero Spin
The relativistic approach to electroweak properties of two-particle composite
systems developed in previous work is generalized here to the case of nonzero
spin. This approach is based on the use of the instant form of relativistic
Hamiltonian dynamics. The generalization makes use of a special mathematical
technique for the parametrization of matrix elements of electroweak current
operators in terms of form factors. In this technique the parametrization is a
realization of theWigner--Eckart theorem on the Poincar\'e group and form
factors are reduced matrix elements. As in the case of zero spin the
electroweak current matrix element satisfies the relativistic covariance
conditions and in the case of electromagnetic current it also automatically
satisfies the conservation law. Physical approximations such as, for example,
the relativistic impulse approximation, are formulated in terms of reduced
matrix elements. The electromagnetic structure of meson is calculated as
an example of realization of the technique proposed.Comment: 20 pages, 4 figures, 1 table. This is the second part of the paper
published in Phys.Rev.C 65, 045501 (2002
IceCube astrophysical neutrinos without a spectral cutoff and (10^15-10^17) eV cosmic gamma radiation
We present a range of unbroken power-law fits to the astrophysical-neutrino
spectrum consistent with the most recent published IceCube data at the 68\%
confidence level. Assuming that the neutrinos originate in decays of pi mesons,
we estimate accompanying gamma-ray fluxes for various distributions of sources,
taking propagation effects into account. We then briefly discuss existing
experimental results constraining PeV to EeV diffuse gamma-ray flux and their
systematic uncertainties. Several scenarios are marginally consistent both with
the KASKADE and CASA-MIA upper limits at (10^15-10^16) eV and with the EAS-MSU
tentative detection at ~10^17 eV, given large systematic errors of the
measurements. Future searches for the diffuse gamma-ray background at sub-PeV
to sub-EeV energies just below present upper limits will give a crucial
diagnostic tool for distinguishing between the Galactic and extragalactic
models of the origin of the IceCube events.Comment: 11 pages, 3 figures, revtex. V.2: references added and correcte
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