426 research outputs found
Leptogenesis, neutrino masses and gauge unification
Leptogenesis is considered in its natural context where Majorana neutrinos
fit in a gauge unification scheme and therefore couple to some extra gauge
bosons. The masses of some of these gauge bosons are expected to be similar to
those of the heavy Majorana particles, and this can have important consequences
for leptogenesis. In fact, the effect can go both ways. Stricter bounds are
obtained on one hand due to the dilution of the CP-violating effect by new
decay and scattering channels, while, in a re-heating scheme, the presence of
gauge couplings facilitates the re-population of the Majorana states. The
latter effect allows in particular for smaller Dirac couplings.Comment: 11pages, 7 figures. v2: definition of the lepton asymmetry corrected,
small numerical changes for the baryon number, conclusion does not change;
typos corrected and references adde
Neutrinos in flat extra dimension: towards a realistic scenario
We consider the simple extension of the Standard Model in which an additional
right handed neutrino propagates along a flat extra dimension, while the
Standard Model fields are confined on a 3-brane. The fifth dimension is
orbifold compactified. In this scenario, the neutrino mass can be
naturally suppressed. By studying systematically the fundamental parameter
space, we show that the strong phenomenological constraints on mixing angles
between active and sterile neutrinos (especially those derived from the SNO
experiment data) do not conflict with the possibility of generating a realistic
neutrino mass spectrum. As a second step, we explore the possibility of a
successful leptogenesis through the decays of the Kaluza-Klein excitations of
the right handed neutrino.Comment: 16 pages, 2 ps figure
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
CP Violation beyond the Standard Model
In this talk a number of broad issues are raised about the origins of CP
violation and how to test the ideas.Comment: 17 pages, LaTeX, 6 postscript figures. Uses iopart10.clo,
iopart12.clo and iopart.cls. Plenary talk given at the BSM Phenomenology
Workshop, Durham, UK, 6-11 May 2001. To appear in the proceeding
Angular Momentum Conservation Law for Randall-Sundrum Models
In Randall-Sundrum models, by the use of general Noether theorem, the
covariant angular momentum conservation law is obtained with the respect to the
local Lorentz transformations. The angular momentum current has also
superpotential and is therefore identically conserved. The space-like
components of the angular momentum for Randall-Sundrum models are
zero. But the component is infinite.Comment: 10 pages, no figures, accepted by Mod. Phys. Lett.
Enhanced baryon number violation due to cosmological defects with localized fermions along extra dimension
We propose a new scenario of baryon number violation in models with extra
dimensions. In the true vacuum, baryon number is almost conserved due to the
localization mechanism of matter fields, which suppresses the interactions
between quarks and leptons. We consider several types of cosmological defects
in four-dimensional spacetime that shift the center of the localized matter
fields, and show that the magnitudes of the baryon number violating
interactions are well enhanced. Application to baryogenesis is also discussed.Comment: 12pages, latex2e, added references, to appear in PR
Thermal production of axino Dark Matter
We reconsider thermal production of axinos in the early universe, adding: a)
missed terms in the axino interaction; b) production via gluon decays
kinematically allowed by thermal masses; c) a precise modeling of reheating. We
find an axino abunance a few times larger than previous computations.Comment: 6 pages, 2 figures. Final version, to appear on JHE
b-physics signals of the lightest CP-odd Higgs in the NMSSM at large tan beta
We investigate the low energy phenomenology of the lighter pseudoscalar
in the NMSSM. The mass can naturally be small due to a global
symmetry of the Higgs potential, which is only broken by trilinear
soft terms. The mass is further protected from renormalization group
effects in the large limit. We calculate the
amplitude at leading order in and work out the contributions to
rare , and radiative -decays and mixing. We obtain
constraints on the mass and couplings and show that masses down to
MeV are allowed. The -physics phenomenology of the NMSSM
differs from the MSSM in the appearance of sizeable renormalization effects
from neutral Higgses to the photon and gluon dipole operators and the breakdown
of the MSSM correlation between the branching ratio and
mixing. For masses above the tau threshold the
can be searched for in processes with branching ratios
\lsim 10^{-3}.Comment: 18 pages, 3 figures; references adde
Supersymmetric Relations Among Electromagnetic Dipole Operators
Supersymmetric contributions to all leptonic electromagnetic dipole operators
have essentially identical diagramatic structure. With approximate slepton
universality this allows the muon anomalous magnetic moment to be related to
the electron electric dipole moment in terms of supersymmetric phases, and to
radiative flavor changing lepton decays in terms of small violations of slepton
universality. If the current discrepancy between the measured and Standard
Model values of the muon anomalous magnetic moment is due to supersymmetry, the
current bound on the electron electric dipole moment then implies that the
phase of the electric dipole operator is less than . Likewise
the current bound on decay implies that the fractional
selectron-smuon mixing in the left-left mass squared matrix, \delta m_{\smuon
\selectron}^2 / m_{\slepton}^2, is less than . These relations and
constraints are fairly insensitive to details of the superpartner spectrum for
moderate to large .Comment: Latex, 38 pages, 2 figure
Fermion masses and quantum numbers from extra dimensions
We study the localization of fermions on a brane embedded in a space-time
with geometry. Quantum numbers of localized fermions are
associated with their rotation momenta around the brane. Fermions with
different quantum numbers have different higher-dimensional profiles. Fermion
masses and mixings, which are proportional to the overlap of higher-dimensional
profiles of the fermions, depend on the fermion quantum numbers.Comment: 14 page
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