3,972 research outputs found
Neutrino masses and mixing angles from leptoquark interactions
In this paper we show that the mixing between leptoquarks (LQ's) from
different multiplets can generate a non-trivial Majorana mass matrix
for neutrinos through one loop self energy diagrams. Such mixing can arise from
gauge invariant and renormalizable LQ-Higgs interaction terms after EW symmetry
breaking. We use the experimental indication on neutrino oscillation to find
constraints on specific combinations of LQ couplings to quark-lepton pairs and
to the SM higgs boson. These constraints are compared with the ones from
.Comment: The expressions for majorana mass matrix of neutrinos have been
corrected so that they are symmetric. Final version to be published in
Physical Review
Stau-catalyzed Li Production in Big-Bang Nucleosynthesis
If the gravitino mass is in the region from a few GeV to a few 10's GeV, the
scalar lepton X such as stau is most likely the next lightest supersymmetry
particle. The negatively charged and long-lived X^- may form a Coulomb bound
state (A X) with a nucleus A and may affect the big-bang nucleosynthesis
through catalyzed fusion process. We calculate a production cross section of
Li6 from the catalyzed fusion (He4 X^-) + d \to Li6 + X^- by solving the
Schr\"{o}dinger equation exactly for three-body system of He4, d, and X. We
utilize the state-of-the-art coupled-channel method, which is known to be very
accurate to describe other three-body systems in nuclear and atomic reactions.
The importance of the use of appropriate nuclear potential and the exact
treatment of the quantum tunneling in the fusion process are emphasized. We
find that the astrophysical S-factor at the Gamow peak corresponding to T=10
keV is 0.038 MeV barn. This leads to the Li6 abundance from the catalyzed
process as Li6|_{CBBN}\simeq 4.3\times 10^{-11} (D/2.8\times 10^{-5})
([n_{X^-}/s]/10^{-16}) in the limit of long lifetime of X. Particle physics
implication of this result is also discussed.Comment: 16 pages, 7 figure
Leptogenesis with Almost Degenerate Majorana Neutrinos
We investigate the leptogenesis with almost degenerate neutrinos, in the
framework of democratic mass matrix, which naturally explains the large mixing
angles for neutrino oscillations as well as quark masses and mixing matrix. We
find that the baryon asymmetry in the present universe is explained via the
decays of right-handed neutrinos produced nonthermally by the inflaton decay.
The model predicts neutrinoless double beta decays accessible in near future
experiments.Comment: 17 pages, LaTeX, 2 figure
CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis
We obtain the Boltzmann equations for leptogenesis including decay and
scattering processes with two and three body initial or final states. We
present an explicit computation of the CP violating scattering asymmetries. We
analyze their possible impact in leptogenesis, and we discuss the validity of
their approximate expressions in terms of the decay asymmetry. In scenarios in
which the initial heavy neutrino density vanishes, the inclusion of CP
asymmetries in scatterings can enforce a cancellation between the lepton
asymmetry generated at early times and the asymmetry produced at later times.
We argue that a sizeable amount of washout is crucial for spoiling this
cancellation, and we show that in the regimes in which the washouts are
particularly weak, the inclusion of CP violation in scatterings yields a
reduction in the final value of the lepton asymmetry. In the strong washout
regimes the inclusion of CP violation in scatterings still leads to a
significant enhancement of the lepton asymmetry at high temperatures; however,
due to the independence from the early conditions that is characteristic of
these regimes, the final value of the lepton asymmetry remains approximately
unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and
corresponding figures (mainly fig. 3) corrected. Final version to be
published in JHE
Heavy quark production via leptoquarks at a neutrino factory
The proposed neutrino factory (NF) based on a muon storage ring (MSR) is an
ideal place to look for heavy quark production via neutral current (NC) and
charged current (CC) interactions. In this article, we address the issue of
contribution coming from mediating leptoquarks (LQ) in interactions leading to the production of at a
MSR and investigate the region where LQ interactions are significant in the
near-site experiments.Comment: 12 pages latex, 10 ps figures, uses axocolour.sty, Slightly revised
version to appear in PR
Analysis of a model with a common source of CP violation
We work in a model where all CP violating phenomena have a common source. CP
is spontaneously broken at a large scale through the phase of a complex
singlet scalar. An additional singlet vector-like down-type quark
relates this high scale CP violation to low energy. We quantitatively analyze
this model in the quark sector. We obtain the numerical values of the
parameters of the Lagrangian in the quark sector for a specific ansatz of the
down-type quark mass matrix where the weak phase is generated
minimally. vertex will modify in presence of the extra vector-like
down-type quark. From the experimental lower bound of the partial decay width
we find out the lower bound of the additional down-type quark
mass. Tree level flavor changing neutral current appears in this model due to
the presence of the extra vector-like down-type quark. We give the range of
values of the mass splitting in system
using SM box, mediating tree level and mediating one loop diagrams
together for both . We find out the analytical expression for
in this model from standard box, and Higgs mediated penguin
diagrams for system, . From this we numerically
evaluate the decay width difference . We
also find out the numerical values of the CP asymmetry parameters and
for the decays and
respectively. We get the lower bound of the scale through the upper bound
of the strong CP phase.Comment: 20 pages, no figures New materials and references have been added.
Text has been modified. To be appear in J.Phys.
HELAS and MadGraph with spin-3/2 particles
Fortran subroutines to calculate helicity amplitudes with massive spin-3/2
particles, such as massive gravitinos, which couple to the standard model and
supersymmetric particles via the supercurrent, are added to the HELAS (HELicity
Amplitude Subroutines) library. They are coded in such a way that arbitrary
amplitudes with external gravitinos can be generated automatically by MadGraph,
after slight modifications. All the codes have been tested carefully by making
use of the gauge invariance of the helicity amplitudes.Comment: 12 pages, 4 figures; sections rearranged, typos corrected, version to
appear in EPJ
Exploring the SO(32) Heterotic String
We give a complete classification of Z_N orbifold compactification of the
heterotic SO(32) string theory and show its potential for realistic model
building. The appearance of spinor representations of SO(2n) groups is analyzed
in detail. We conclude that the heterotic SO(32) string constitutes an
interesting part of the string landscape both in view of model constructions
and the question of heterotic-type I duality.Comment: 21 pages, 5 figure
Neutrino Parameters, Abelian Flavor Symmetries, and Charged Lepton Flavor Violation
Neutrino masses and mixings have important implications for models of fermion
masses, and, most directly, for the charged lepton sector. We consider
supersymmetric Abelian flavor models, where neutrino mass parameters are
related to those of charged leptons and sleptons. We show that processes such
as \tau to \mu\gamma, \mu to e\gamma and \mu-e conversion provide interesting
probes. In particular, some existing models are excluded by current bounds,
while many others predict rates within reach of proposed near future
experiments. We also construct models in which the predicted rates for charged
lepton flavor violation are below even the proposed experimental sensitivities,
but argue that such models necessarily involve loss of predictive power.Comment: 27 pages, refs added, published versio
Gravitino constraints on models of neutrino masses and leptogenesis
In the supersymmetric extensions of the standard model, neutrino masses and
leptogenesis requires existence of new particles. We point out that if these
particles with lepton number violating interactions have standard model gauge
interactions, then they may not be created after reheating because of the
gravitino problem. This will rule out all existing models of neutrino masses
and leptogenesis, except the one with right-handed singlet neutrinos.Comment: 12 pages latex file with one postscript figur
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