49 research outputs found
A Mechanism for Baryogenesis in Low Energy Supersymmetry Breaking Models
A generic prediction of models where supersymmetry is broken at scales within
a few orders of magnitude of the weak scale and is fed down to the observable
sector by gauge interactions is the existence of superconducting cosmic strings
which carry baryon number. In this paper we propose a novel mechanism for the
generation of the baryon asymmetry which takes place at temperatures much lower
than the weak scale. Superconducting strings act like ``bags'' containing the
baryon charge and protect it from sphaleron wash-out throughout the evolution
of the Universe, until baryon number violating processes become harmless. This
mechanism is efficient even if the electroweak phase transition in the MSSM is
of the second order and therefore does not impose any upper bound on the mass
of the Higgs boson. (13kb)Comment: LaTeX file, 17 pages. One ref. adde
Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale
We investigate what could be learned about the absolute scale of neutrino
masses from comparisons among the patterns within quark and lepton mass
hierarchies. First, we observe that the existing information on neutrino masses
fits quite well to the unexplained, but apparently present regularities in the
quark and charged lepton sectors. Second, we discuss several possible mass
patterns, pointing out that this quite generally leads towards hierarchical
neutrino mass patterns especially disfavoring the vacuum solution.Comment: final version to be published in PRD, 5 pages, 2 figures, RevTe
On the structure of the scalar mesons and
We investigate the structure of the scalar mesons and
within realistic meson-exchange models of the and
interactions. Starting from a modified version of the J\"ulich model for
scattering we perform an analysis of the pole structure of the
resulting scattering amplitude and find, in contrast to existing models, a
somewhat large mass for the ( MeV,
MeV). It is shown that our model provides a description of
data comparable in quality with those of
alternative models. Furthermore, the formalism developed for the
system is consistently extended to the interaction leading to a
description of the as a dynamically generated threshold effect
(which is therefore neither a conventional state nor a
bound state). Exploring the corresponding pole position the
is found to be rather broad ( MeV,
MeV). The experimentally observed smaller width results from the influence of
the nearby threshold on this pole.Comment: 25 pages, 15 Postscript figure
Atmospheric and Solar Neutrino Masses from Horizontal U(1) Symmetry
We study the neutrino mass matrix in supersymmetric models in which the quark
and charged lepton mass hierarchies and also the suppression of baryon or
lepton number violating couplings are all explained by horizontal
symmetry. It is found that the neutrino masses and mixing angles suggested by
recent atmospheric and solar neutrino experiments arise naturally in this
framework which fits in best with gauge-mediated supersymmetry breaking with
large . This framework highly favors the small angle MSW oscillation
of solar neutrinos, and determine the order of magnitudes of all the neutrino
mixing angles and mass hierarchies.Comment: No figures. 14 pages, revte
Mass matrix Ansatz and lepton flavor violation in the THDM-III
Predictive Higgs-fermion couplings can be obtained when a specific texture
for the fermion mass matrices is included in the general two-Higgs doublet
model. We derive the form of these couplings in the charged lepton sector using
a Hermitian mass matrix Ansatz with four-texture zeros. The presence of
unconstrained phases in the vertices phi-li-lj modifies the pattern of
flavor-violating Higgs interactions. Bounds on the model parameters are
obtained from present limits on rare lepton flavor violating processes, which
could be extended further by the search for the decay tau -> mu mu mu and mu-e
conversion at future experiments. The signal from Higgs boson decays phi -> tau
mu could be searched at the large hadron collider (LHC), while e-mu transitions
could produce a detectable signal at a future e mu-collider, through the
reaction e mu -> h0 -> tau tau.Comment: 17 pages, 9 figure
S_3 Symmetry and Neutrino Masses and Mixings
Based on a universal seesaw mass matrix model with three scalars \phi_i, and
by assuming an S_3 flavor symmetry for the Yukawa interactions, the lepton
masses and mixings are investigated systematically. In order to understand the
observed neutrino mixing, the charged leptons (e, \mu, \tau) are regarded as
the 3 elements (e_1, e_2, e_3) of S_3, while the neutrino mass-eigenstates are
regarded as the irreducible representation (\nu_\eta, \nu_\sigma, \nu_\pi) of
S_3, where (\nu_\pi, \nu_\eta) and \nu_\sigma are a doublet and a singlet,
respectively, which are composed of the 3 elements (\nu_1, \nu_2, \nu_3) of
S_3.Comment: 16 pages, no figure, version to appear in EPJ-
Tribimaximal Neutrino Mixing and a Relation Between Neutrino- and Charged Lepton-Mass Spectra
Brannen has recently pointed out that the observed charged lepton masses
satisfy the relation m_e +m_\mu +m_\tau = {2/3}
(\sqrt{m_e}+\sqrt{m_\mu}+\sqrt{m_\tau})^2, while the observed neutrino masses
satisfy the relation m_{\nu 1} +m_{\nu 2} +m_{\nu 3} = {2/3} (-\sqrt{m_{\nu
1}}+\sqrt{m_{\nu 2}}+\sqrt{m_{\nu 3}})^2. It is discussed what neutrino Yukawa
interaction form is favorable if we take the fact pointed out by Brannen
seriously.Comment: 13 pages, presentation modifie
Meson-meson scattering within one loop Chiral Perturbation Theory and its unitarization
We present the complete one-loop calculation of all the two meson scattering
amplitudes within the framework of SU(3) Chiral Perturbation Theory, which
includes pions, kaons and the eta. In addition, we have unitarized these
amplitudes with the coupled channel Inverse Amplitude Method, which ensures
simultaneously the good low energy properties of Chiral Perturbation Theory and
unitarity. We show how this method provides a remarkable description of
meson-meson scattering data up to 1.2 GeV including the scattering lengths and
the generation of seven light resonances, which is consistent with previous
determination of the chiral parameters. Particular attention is paid to discuss
the differences and similarities of this work with previous analysis in the
literature.Comment: 20 pages, 5 figures. Comments on sigma, kappa and eta', as well as
some references added. Final version to appear in Phys.Rev.
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
Leptogenesis and Neutrino Oscillations Within A Predictive G(224)/SO(10)-Framework
A framework based on an effective symmetry that is either G(224)= SU(2)_L x
SU(2)_R xSU(4)^c or SO(10) has been proposed (a few years ago) that
successfully describes the masses and mixings of all fermions including
neutrinos, with seven predictions, in good accord with the data. Baryogenesis
via leptogenesis is considered within this framework by allowing for natural
phases (~ 1/20-1/2) in the entries of the Dirac and Majorana mass-matrices. It
is shown that the framework leads quite naturally, for both thermal as well as
non-thermal leptogenesis, to the desired magnitude for the baryon asymmetry.
This result is obtained in full accord with the observed features of the
atmospheric and solar neutrino oscillations, as well as with those of the quark
and charged lepton masses and mixings, and the gravitino-constraint. Hereby one
obtains a unified description of fermion masses, neutrino oscillations and
baryogenesis (via leptogenesis) within a single predictive framework.Comment: Efficiency factor updated, some clarifications and new references
added. 19 page