214 research outputs found
Dark matter assisted Dirac leptogenesis and neutrino mass
We propose a minimal extension of the standard model with U(1)_{B-L} \times
Z_{2} symmetry. In this model by assuming that the neutrinos are Dirac (i.e.
is an exact symmetry), we found a simultaneous solution for non zero
neutrino masses and dark matter content of the universe. The observed baryon
asymmetry of the universe is also explained using Dirac Leptogenesis, which is
assisted by a dark sector, gauged under a U(1)_D symmetry. The latter symmetry
of the dark sector is broken at a TeV scale and thereby giving mass to a
neutral gauge boson Z_D. The standard model Z-boson mixes with the gauge boson
Z_D at one loop level and thus paves a way to detect the dark matter through
spin independent elastic scattering at terrestrial laboratories.Comment: 12 pages, 10 figures. Accepted for publication in Nuclear Physics
keV Warm Dark Matter via the Supersymmetric Higgs Portal
Warm dark matter (WDM) may resolve the possible conflict between observed
galaxy halos and the halos produced in cold dark matter (CDM) simulations. Here
we present an extension of MSSM to include WDM by adding a gauge singlet
fermion, \bar{\chi}, with a portal-like coupling to the MSSM Higgs doublets.
This model has the property that the dark matter is {\it necessarily warm}. In
the case where M_{\bar{\chi}} is mainly due to electroweak symmetry breaking,
the \bar{\chi} mass is completely determined by its relic density and the
reheating temperature, T_R. For 10^2 GeV < T_{R} < 10^{5} GeV$, the range
allowed by \bar{chi} production via thermal Higgs annihilation, the \bar{\chi}
mass is in the range 0.3-4 keV, precisely the range required for WDM. The
primordial phase-space density, Q, can directly account for that observed in
dwarf spheroidal galaxies, Q \approx 5 x 10^{6}(eV/cm^3)/(km/s)^3,, when the
reheating temperature is in the range T_R \approx 10-100 TeV, in which case
M_{\bar{\chi}} \approx 0.45 keV. The free-streaming length is in the range
0.3-4 Mpc, which can be small enough to alleviate the problems of
overproduction of galaxy substructure and low angular momentum of CDM
simulations.Comment: 6 pages LaTeX, Significantly expanded discussion. To be published in
Physical Review
Predictive model for dark matter, dark energy, neutrino masses and leptogenesis at the TeV scale
We propose a new mechanism of TeV scale leptogenesis where the chemical
potential of right-handed electron is passed on to the asymmetry of the
Universe in the presence of sphalerons. The model has the virtue that the
origin of neutrino masses are independent of the scale of leptogenesis. As a
result, the model could be extended to explain {\it dark matter, dark energy,
neutrino masses and leptogenesis at the TeV scale}. The most attractive feature
of this model is that it predicts a few hundred GeV triplet Higgs scalar that
can be tested at LHC or ILC.Comment: 5 pages (revtex), double column, 2 eps figures, journal version. To
appear in Phys. ReV.
TeV scale model for neutrino masses, dark matter and leptogenesis
We present a TeV scale model for leptogenesis where the origin of neutrino
masses are independent of the scale of leptogenesis. As a result, the model
could be extended to explain {\it dark matter, neutrino masses and leptogenesis
at the TeV scale}. The most attractive feature of this model is that it
predicts a few hundred GeV triplet Higgs scalar that can be tested at LHC or
ILC.Comment: 4 pages, contribution to International workshop on theoretical high
energy physics (IWTHEP), Roorkee, 200
Gravitino production in an inflationary Universe and implications for leptogenesis
Models of leptogenesis are constrained by the low reheat temperature at the
end of reheating associated with the gravitino bound. However a detailed view
of reheating, in which the maximum temperature during reheating, \Tmax, can
be orders of magnitude higher than the reheat temperature, allows for the
production of heavy Majorana neutrinos needed for leptogenesis. But then one
must also consider the possibility of enhanced gravitino production in such
scenarios. In this article we consider gravitino production during reheating,
its dependence on \Tmax, and its relevance for leptogenesis. Earlier
analytical studies of the gravitino abundance have only considered gravitino
production in the post-reheating radiation dominated era. We find that the
gravitino abundance generated during reheating is comparable to that generated
after reheating. This lowers the upper bound on the reheat temperature by a
factor of 4/3.Comment: Journal version, minor change in title, 13 pages (revtex), 2 eps
figure
Gauged symmetry and baryogenesis via leptogenesis at TeV scale
It is shown that the requirement of preservation of baryon asymmetry does not
rule out a scale for leptogenesis as low as 10 TeV. The conclusions are
compatible with see-saw mechanism if for example the pivot mass scale for
neutrinos is that of the charged leptons. We explore the
parameter space - of relevant light and heavy neutrino masses
by solving Boltzmann equations. A viable scenario for obtaining baryogenesis in
this way is presented in the context of gauged symmetry.Comment: 15 pages, 4 figures, references added, match with journal versio
Cosmic Ray Anomalies and Dark Matter Annihilation to Muons via a Higgs Portal Hidden Sector
Annihilating dark matter (DM) models based on a scalar hidden sector with
Higgs portal-like couplings to the Standard Model are considered as a possible
explanation for recently observed cosmic ray excesses. Two versions of the
model are studied, one with non-thermal DM as the origin of the boost factor
and one with Sommerfeld enhancement. In the case of non-thermal DM, four hidden
sector scalars which transform under a U(1)_{X} symmetry are added. The
heaviest scalars decouple and later decay to DM scalars, so providing the boost
factor necessary to explain the present DM annihilation rate. The mass of the
annihilating scalars is limited to < 600 GeV for the model to remain
perturbative. U(1)_{X} breaking to Z_2 at the electroweak transition mixes
light O(100) MeV hidden sector scalars with the Higgs. The DM scalars
annihilate to these light scalars, which subsequently decay to two mu^{+}
mu^{-} pairs via Higgs mixing, so generating a positron excess without
antiprotons. Decay to \mu^{+}\mu^{-} rather than e^{+}e^{-} is necessary to
ensure a fast enough light scalar decay rate to evade light scalar domination
at nucleosynthesis. In the version with Sommerfeld enhancement only three new
scalars are necessary. TeV scale DM masses can be accomodated, allowing both
the higher energy electron plus positron excess and the lower energy PAMELA
positron excess to be explained. DM annihilates to two \mu^{+}\mu^{-} pairs as
in the non-thermal model. This annihilation mode may be favoured by recent
observations of the electron plus positron excess by FERMI and HESS.Comment: 24 pages, 4 figures. Expanded discussion, conclusions unchanged.
Version to be published in Physical Review
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