370 research outputs found
Neutrino Mass Patterns within the See-saw Model from Multi-localization along Extra Dimensions
We study a multi-localization model for charged leptons and neutrinos,
including the possibility of a see-saw mechanism. This framework offers the
opportunity to allow for realistic solutions in a consistent model without
fine-tuning of parameters, even if quarks are also considered. Those solutions
predict that the large Majorana mass eigenvalues for right-handed neutrinos are
of the same order of magnitude, although this almost common mass can span a
large range (bounded from above by ). The model also
predicts Majorana masses between and $\sim 5 \
10^{-2}{\rm eV}\beta\theta_{13}10^{-2} \lesssim
\sin \theta_{13} \lesssim 10^{-1}$, but smaller values are not totally excluded
by the model.Comment: 36 pages, 8 figure
Halo Geometry and Dark Matter Annihilation Signal
We study the impact of the halo shape and geometry on the expected weakly
interacting massive particle (WIMP) dark matter annihilation signal from the
galactic center. As the halo profile in the innermost region is still poorly
constrained, we consider different density behaviors like flat cores, cusps and
spikes, as well as geometrical distortions. We show that asphericity has a
strong impact on the annihilation signal when the halo profile near the
galactic center is flat, but becomes gradually less significant for cuspy
profiles, and negligible in the presence of a central spike. However, the
astrophysical factor is strongly dependent on the WIMP mass and annihilation
cross-section in the latter case.Comment: 5 pages, 4 figures, PR
MeV Right-handed Neutrinos and Dark Matter
We consider the possibility of having a MeV right-handed neutrino as a dark
matter constituent. The initial reason for this study was the 511 keV spectral
line observed by the satellite experiment INTEGRAL: could it be due to an
interaction between dark matter and baryons? Independently of this, we find a
number of constraints on the assumed right-handed interactions. They arise in
particular from the measurements by solar neutrino experiments. We come to the
conclusion that such particles interactions are possible, and could reproduce
the peculiar angular distribution, but not the rate of the INTEGRAL signal.
However, we stress that solar neutrino experiments are susceptible to provide
further constraints in the future.Comment: 7 pages, figure 1 changed, added reference
Flavour Matters in Leptogenesis
We give analytic approximations to the baryon asymmetry produced by thermal
leptogenesis with hierarchical right-handed neutrinos. Our calculation includes
flavour-dependent washout processes and CP violation in scattering, and
neglects gauge interactions and finite temperature corrections. Our approximate
formulae depend upon the three CP asymmetries in the individual lepton flavours
as well as on three flavour-dependent efficiency factors. We show that the
commonly used expressions for the lepton asymmetry, which depend on the total
CP asymmetry and one single efficiency factor, may fail to reproduce the
correct lepton asymmetry in a number of cases. We illustrate the importance of
using the flavour-dependent formulae in the context of a two right-handed
neutrino model.Comment: Additional typos corrected (in particular, the plots and captions now
agree
Right-Handed Sector Leptogenesis
Instead of creating the observed baryon asymmetry of the universe by the
decay of right-handed (RH) neutrinos to left-handed leptons, we propose to
generate it dominantly by the decay of the RH neutrinos to RH leptons. This
mechanism turns out to be successful in large regions of parameter space. It
may work, in particular, at a scale as low as ~TeV, with no need to
invoke quasi-degenerate RH neutrino masses to resonantly enhance the asymmetry.
Such a possibility can be probed experimentally by the observation at colliders
of a singlet charged Higgs particle and of RH neutrinos. Other mechanisms which
may lead to successful leptogenesis from the RH lepton sector interactions are
also briefly presented. The incorporation of these scenarios in left-right
symmetric and unified models is discussed.Comment: 14 pages, latex, axodraw; minor clarifications and references added,
extended discussion of the signatures at collider
Observable Electron EDM and Leptogenesis
In the context of the minimal supersymmetric seesaw model, the CP-violating
neutrino Yukawa couplings might induce an electron EDM. The same interactions
may also be responsible for the generation of the observed baryon asymmetry of
the Universe via leptogenesis. We identify in a model-independent way those
patterns within the seesaw models which predict an electron EDM at a level
probed by planned laboratory experiments and show that negative searches on
\tau-> e \gamma decay may provide the strongest upper bound on the electron
EDM. We also conclude that a possible future detection of the electron EDM is
incompatible with thermal leptogenesis, even when flavour effects are accounted
for.Comment: 26 pages, 6 figure
Leptogenesis and symmetry
If an exact symmetry is the explanation of the
maximal atmospheric neutrino mixing angle, it has interesting implications for
origin of matter via leptogenesis in models where small neutrino masses arise
via the seesaw mechanism. For seesaw models with two right handed neutrinos
, lepton asymmetry vanishes in the exact symmetric limit, even though there are nonvanishing Majorana phases in
the neutrino mixing matrix. On the other hand, for three right handed neutrino
models, lepton asymmetry nonzero and is given directly by the solar mass
difference square. We also find an upper bound on the lightest neutrino mass.Comment: 5 pages; latex; no figures; some typos correcte
A Brief Review on Dark Matter Annihilation Explanation for Excesses in Cosmic Ray
Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are
excesses in the cosmic ray energy spectrum. PAMELA observed excesses
only in , but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS
observed excesses in spectrum, but the detailed shapes are different
which requires future experimental observations to pin down the correct data
set. Nevertheless a lot of efforts have been made to explain the observed
excesses, and also why PAMELA only observed excesses in but not
in anti-proton. In this brief review we discuss one of the most popular
mechanisms to explain the data, the dark matter annihilation. It has long been
known that about 23% of our universe is made of relic dark matter. If the relic
dark matter was thermally produced, the annihilation rate is constrained
resulting in the need of a large boost factor to explain the data. We will
discuss in detail how a large boost factor can be obtained by the Sommerfeld
and Briet-Wigner enhancement mechanisms. Some implications for particle physics
model buildings will also be discussed.Comment: 22 pages, 6 figures. Several typoes corrected and some references
added. Published in Mod. Phys. Lett. A, Vol. 24, No. 27 (2009) pp. 2139-216
Adiabatic compression and indirect detection of supersymmetric dark matter
Recent developments in the modelling of the dark matter distribution in our
Galaxy point out the necessity to consider some physical processes to satisfy
observational data. In particular, models with adiabatic compression, which
include the effect of the baryonic gas in the halo, increase significantly the
dark matter density in the central region of the Milky Way. On the other hand,
the non-universality in scalar and gaugino sectors of supergravity models can
also increase significantly the neutralino annihilation cross section. We show
that the combination of both effects gives rise to a gamma-ray flux arising
from the Galactic Center largely reachable by future experiments like GLAST. We
also analyse in this framework the EGRET excess data above 1 GeV, as well as
the recent data from CANGAROO and HESS. The analysis has been carried out
imposing the most recent experimental constraints, such as the lower bound on
the Higgs mass, the \bsg branching ratio, and the muon . In addition, the
recently improved upper bound on has also been taken
into account. The astrophysical (WMAP) bounds on the dark matter density have
also been imposed on the theoretical computation of the relic neutralino
density through thermal production.Comment: 32 pages, 11 figures, final version to appear in JCA
Neutrino Oscillations v.s. Leptogenesis in SO(10) Models
We study the link between neutrino oscillations and leptogenesis in the
minimal framework assuming an SO(10) see-saw mechanism with 3 families. Dirac
neutrino masses being fixed, the solar and atmospheric data then generically
induce a large mass-hierarchy and a small mixing between the lightest
right-handed neutrinos, which fails to produce sufficient lepton asymmetry by 5
orders of magnitudes at least. This failure can be attenuated for a very
specific value of the mixing sin^2(2\theta_{e3})=0.1, which interestingly lies
at the boundary of the CHOOZ exclusion region, but will be accessible to future
long baseline experiments.Comment: 23 pages, 8 eps figures, JHEP3 format; more accurate effect of
dilution reduces previous results, inclusion of all phases, added reference
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