3,872 research outputs found
The importance of flavor in leptogenesis
We study leptogenesis from the out-of-equilibrium decays of the lightest
heavy neutrino in the medium (low) temperature regime, T\lsim 10^{12}
GeV ( GeV), where the rates of processes mediated by the (and
) Yukawa coupling are non negligible, implying that the effects of lepton
flavors must be taken into account. We find important quantitative and
qualitative differences with respect to the case where flavor effects are
ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of
magnitude; (ii) The sign of the asymmetry can be opposite to what one would
predict from the sign of the total lepton asymmetry ; (iii)
Successful leptogenesis is possible even with .Comment: 27 pages, 2 figures. Added 3 reference
Hadronic mass and q^2 moments of charmless semileptonic B decay distributions
We report OPE predictions for hadronic mass and q^2 moments in inclusive
semileptonic B decays without charm, taking into account experimental cuts on
the charged lepton energy and on the hadronic invariant mass, and address the
related theoretical uncertainty.Comment: 16 pages, 1 figure; v3: we have corrected a mistake in the code that
produced the numerical results; tables replaced, small changes in the tex
Leptoquark Contribution to the Higgs Boson Production at the LHC Collider
In this report we study how a light-scalar leptoquark could affect the Higgs
boson production cross-section at the LHC collider. We construct the most
general renormalizable and gauge invariant effective Lagrangian involving the
standard model particles and a scalar, isoscalar leptoquark, \eta.
The total cross-section for pp -> H+X is then calculated for different values
of the unknown parameters \lambda_eta, m_eta and m_H.(Here \lambda_eta is the
coupling associated with the Higgs-leptoquark interaction.)
We find that if \lambda_eta is moderately large and m_eta is around a few
hundred GeV, then the cross-section is significantly larger than the standard
model value.Comment: 9 pages, 4 postscript figure
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.
Screening of Z(N) monopole pairs in gauge theories
The screening of magnetic Z(N)-monopoles and the associated screening length
in SU(N) gauge theories are analyzed theoretically, and computed numerically in
the 3d SU(2) theory. The nature of the screening excitations as well as their
mass have so far remained inconclusive in the literature. Here we show that the
screening mass is identical to the lowest J^{PC}_R=0^{++}_+ excitation of the
Yang-Mills Hamiltonian with one compact direction with period 1/T, the
subscript R referring to parity in this direction. We extend the continuum
formulation to one on the lattice, and determine the transfer matrix governing
the decay of the spatial monopole correlator at any finite lattice spacing. Our
numerical results for SU(2) for the screening mass in the dimensionally reduced
(high temperature) theory are compatible with the 0^{++} glueball mass in 3d
SU(2).Comment: 24 pages, 3 figures. Typos corrected, published versio
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
Limits on excited tau leptons masses from leptonic tau decays
We study the effects induced by excited leptons on the leptonic tau decay at
one loop level. Using a general effective lagrangian approach to describe the
couplings of the excited leptons, we compute their contributions to the
leptonic decays and use the current experimental values of the branching ratios
to put limits on the mass of excited states and the substructure scale.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
E6,7,8 Magnetized Extra Dimensional Models
We study 10D super Yang-Mills theory with the gauge groups , and
. We consider the torus/orbifold compacfitication with magnetic fluxes and
Wilson lines. They lead to 4D interesting models with three families of quarks
and leptons, whose profiles in extra dimensions are quasi-localized because of
magnetic fluxes.Comment: 17 pages, 1 figur
Unstable Heavy Majorana Neutrinos and Leptogenesis
We propose a new mechanism producing a non-vanishing lepton number asymmetry,
based on decays of heavy Majorana neutrinos. If they are produced out of
equilibrium, as occurs in preheating scenario, and are superpositions of mass
eigenstates rapidly decaying, their decay rates contains interference terms
provided the mass differences are small compared to widths .
The resulting lepton asymmetry, which is the analogue of the time-integrated CP
asymmetry in system, is found to be proportional to .Comment: 18 pages, latex, revised version to be published in Phys. Rev.
Composite Supersymmetric Axion-Dilaton-Dilatino System and the breaking of Supersymmetry
The spontaneous breakdown of the scale, the chiral and the superconformal
symmetries for a hidden gauge group is studied in an effective
lagrangean approach. The relevant low-energy degrees of freedom are taken to be
the composite Goldstone particles associated with these three broken
symmetries. Supersymmetry is spontaneously broken in the large limit and
soft breaking terms in the observable sector are generated, together with
nonrenormalisable Nambu-Jona-Lasinio type interactions.Comment: 20 pages, LPTHE 93/2
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