2,202 research outputs found
Black hole physics, confining solutions of SU(3)-Yang-Mills equations and relativistic models of mesons
The black hole physics techniques and results are applied to find the set of
the exact solutions of the SU(3)-Yang-Mills equations in Minkowski spacetime in
the Lorentz gauge. All the solutions contain only the Coulomb-like or linear in
components of SU(3)-connection. This allows one to obtain some possible
exact and approximate solutions of the corresponding Dirac equation that can
describe the relativistic bound states. Possible application to the
relativistic models of mesons is also outlined.Comment: 13 pages, LaTeX with using the mpla1.sty file from the package of
World Scientific Publishing C
See-Saw Masses for Quarks and Leptons in SU(5)
We build on a recent paper by Grinstein, Redi and Villadoro, where a see-saw
like mechanism for quark masses was derived in the context of spontaneously
broken gauged flavour symmetries. The see-saw mechanism is induced by heavy
Dirac fermions which are added to the Standard Model spectrum in order to
render the flavour symmetries anomaly-free. In this letter we report on the
embedding of these fermions into multiplets of an SU(5) grand unified theory
and discuss a number of interesting consequences.Comment: 15 pages, 4 figures (v3: outline restructured, modified mechanism to
cancel anomalies
Factorization in exclusive semileptonic radiative B decays
We derive a new factorization relation for the semileptonic radiative decay B
-> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda
and an energetic photon E_\gamma >> \Lambda, working at leading order in
\Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element
appearing in this relation can be computed using chiral perturbation theory. We
present a phenomenological study of this decay, which may be important for a
precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde
The eta-photon transition form factor
The eta-photon transition form factor is evaluated in a formalism based on a
phenomenological description at low values of the photon virtuality, and a
QCD-based description at high photon virtualities, matching at a scale
. The high photon virtuality description makes use of a Distribution
Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars
regularization at the matching scale , and QCD evolution from
to higher values of . A good description of the available
data is obtained. The analysis indicates that the recent data from the BaBar
collaboration on pion and eta transition form factor can be well reproduced, if
a small contribution of twist three at the matching scale is
included.Comment: 14 pages, 3 figures, revised version, minor corrections, references
added, conclusions unchanged. Accepted for publication in Phys. Rev.
Study of exclusive processes e^+ e^- \to VP
This paper is devoted to consideration of the hard exclusive processes
, where . Experimental measurement of
the cross section of the process at BaBar collaboration
at large center mass energy GeV and some low energy experimental
data GeV give us the possibility to study the cross section
in the broad energy region. As the result, we have determined the asymptotic
behavior of the cross section of in the limit , which is in agreement with perturbative QCD prediction. Assuming that
the same asymptotic behavior is valid for the other processes under
consideration and using low energy experimental data we have predicted the
cross sections of these processes at energies GeV. In
addition, we have calculated the cross sections of these processes at the same
energies within perturbative QCD. Our results are in agreement with available
experimental data.Comment: 10 pages, 2 tables, 6 figures; minor changes; article accepted to
publication is Phys. Rev.
Properties of the quark-antiquark-gluon Fock state in the \eta_c meson
In this paper the twist-3 distribution amplitude of the quark-antiquark-gluon
Fock state in the \eta_c meson is studied. To calculate the moments of this
distribution amplitude QCD sum rules is applied. Using the results of the
calculation the model of this distribution amplitude is built. In addition
NRQCD matrix elements which determine the properties of the
quark-antiquark-gluon Fock state are determined. In particular, the probability
amplitude to find the quark-antiquark pair in the color octet state, the mean
gluon energy and the fraction of momentum carried by gluon, the relative
velocity of the color-octet quark-antiquark-pair are calculated.Comment: 6 page
Exclusive channels in semi-inclusive production of pions and kaons
We investigate the role of exclusive channels in semi-inclusive
electroproduction of pions and kaons. Using the QCD factorization theorem for
hard exclusive processes we evaluate the cross sections for exclusive
pseudoscalar and vector meson production in terms of generalized parton
distributions and meson distribution amplitudes. We investigate the
uncertainties arising from the modeling of the nonperturbative input
quantities. Combining these results with available experimental data, we
compare the cross sections for exclusive channels to that obtained from quark
fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0
production is the only exclusive channel with significant contributions to
semi-inclusive pion production at large z and moderate Q^2. The corresponding
contribution to kaon production from the decay of exclusively produced phi and
K^* is rather small.Comment: 33 pages, 18 figure
Pseudoscalar Meson Mixing in Effective Field Theory
We show that for any effective field theory of colorless meson fields, the
mixing schemes of particle states and decay constants are not only related but
also determined exclusively by the kinetic and mass Lagrangian densities. In
the general case, these are bilinear in terms of the intrinsic fields and
involve non-diagonal kinetic and mass matrices. By applying three consecutive
steps this Lagrangian can be reduced into the standard quadratic form in terms
of the physical fields. These steps are : (i) the diagonalization of the
kinetic matrix, (ii) rescaling of the fields, and (iii) the diagonalization of
the mass matrix. In case, where the dimensions of the non-diagonal kinetic and
mass sub-matrices are respectively, and , this procedure
leads to mixing schemes which involve angles and
field rescaling parameters. This observation holds true irrespective with the
type of particle interactions presumed. The commonly used mixing schemes,
correspond to a proper choice of the kinetic and mass matrices, and are derived
as special cases. In particular, - mixing, requires one angle, if
and only if, the kinetic term with the intrinsic fields has a quadratic form.Comment: REVTeX, 6 page
Study of Decays in the Family Non-universal Models
In a combined investigation of the decays,
constraints on the related couplings in family non-universal
models are derived. We find that within the allowed parameter space, the
recently observed forward-backward asymmetry in the
decay can be explained, by flipping the signs of the Wilson coefficients
and . With the obtained constraints, we also calculate
the branching ratio of the decay. The upper bound of our
prediction is near the upper bound given by CDF Collaboration recently.Comment: 19 pages, 4 figures, some errors corrected; Journal versio
Quark structure of pseudoscalar mesons
I review to which extent the properties of pseudoscalar mesons can be
understood in terms of the underlying quark (and eventually gluon) structure.
Special emphasis is put on the progress in our understanding of eta-eta'
mixing. Process-independent mixing parameters are defined, and relations
between different bases and conventions are studied. Both, the low-energy
description in the framework of Chiral Perturbation Theory and the high-energy
application in terms of light-cone wave functions for partonic Fock states, are
considered. A thorough discussion of theoretical and phenomenological
consequences of the mixing approach will be given. Finally, I will discuss
mixing with other states pi^0, eta(c), ...).Comment: 48 pages, 7 figures, using epsfig.st
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