198 research outputs found
Neutrino Mass, Leptogenesis and FIMP Dark Matter in a Model
The Standard Model (SM) is inadequate to explain the origin of tiny neutrino
masses, the dark matter (DM) relic abundance and also the baryon asymmetry of
the Universe. In this work to address all the three puzzles, we extend the SM
by a local U gauge symmetry, three right-handed (RH) neutrinos
for the cancellation of gauge anomalies and two complex scalars having nonzero
U charges. All the newly added particles become massive after
the breaking of U symmetry by the vacuum expectation value (VEV)
of one of the scalar fields . The other scalar field , which
does not have any VEV, becomes automatically stable and can be a viable DM
candidate. Neutrino masses are generated using Type-I seesaw mechanism while
the required lepton asymmetry to reproduce the observed baryon asymmetry, can
be attained from the CP violating out of equilibrium decays of RH neutrinos in
TeV scale. More importantly within this framework, we have studied in detail
the production of DM via freeze-in mechanism considering all possible
annihilation and decay processes. Finally, we find a situation when DM is
dominantly produced from the annihilation of RH neutrinos, which are at the
same time also responsible for neutrino mass generation and leptogenesis.Comment: 52 pages, 16 figures, 3 tables, significant modification in the DM
section, matches with the published versio
keV Neutrino Dark Matter in a Fast Expanding Universe
We study the possibility of keV neutrino dark matter in the minimal
gauge extension of the standard model where three right handed
neutrinos are automatically included due to the requirement of anomaly
cancellations. Without considering extra additional particles or symmetries, we
consider the lightest right handed neutrino to be in the keV mass range which
is kinematically long lived. Due to gauge interactions, such a keV neutrino can
be thermally produced in the early Universe followed by decoupling while being
relativistic. The final relic abundance of such keV neutrino typically
overclose the Universe requiring additional mechanism to bring it under
observed limits. We propose a non-standard cosmological history where a scalar
field , that redshifts faster than radiation dominates the Universe prior
to the radiation dominated era. We show that such a non-standard phase can keep
the abundance of thermally generated keV neutrino dark matter within observed
relic abundance. We constrain the non-standard phase, parameters
from these requirements and also briefly comment upon the observational aspects
of such keV neutrino dark matter.Comment: 23 pages, 5 figure
Nonthermal Two Component Dark Matter Model for Fermi-LAT -ray excess and 3.55 keV X-ray Line
A two component model of nonthermal dark matter is formulated to
simultaneously explain the Fermi-LAT results indicating a -ray excess
observed from our Galactic Centre in the 1-3 GeV energy range and the detection
of an X-ray line at 3.55 keV from extragalactic sources. Two additional
Standard Model singlet scalar fields and are introduced. These
fields couple among themselves and with the Standard Model Higgs doublet .
The interaction terms among the scalar fields, namely , and , are
constrained by the application of a discrete symmetry which breaks softly to a remnant
symmetry. This residual discrete symmetry is
then spontaneously broken through an MeV order vacuum expectation value of
the singlet scalar field . The resultant physical scalar spectrum has the
Standard Model like Higgs as with GeV, a moderately heavy scalar with and a light
with keV. There is only tiny mixing between
and as well as between
and . The lack of importance of domain wall formation in the
present scenario from the spontaneous breaking of the discrete symmetry
, provided MeV, is pointed out. We
find that our proposed two component dark matter model is able to explain
successfully both the above mentioned phenomena the Fermi-LAT observed
-ray excess (from the decay mode) and the observation of the X-ray line (from the decay channel
) by the XMM-Newton observatory.Comment: 11 eps Figures, 2 Tables, 32 Pages. Minor addition in Abstract.
Inclusion in Section 1 of discussion of earlier attempts to explain the
concerned phenomena by astrophysical processes. Extension of discussion in
Section 6 to the case of a steeper dark matter density profile. Results
unchanged. Version accepted for publication in JHE
Dwarf Galaxy -excess and 3.55 keV X-ray Line In A Nonthermal Dark Matter Model
Recent data from Reticulum II (RetII) require the energy range of the
FermiLAT -excess to be GeV. We adjust our unified
nonthermal Dark Matter (DM) model to accommodate this. We have two extra
scalars beyond the Standard Model to also explain 3.55 keV X-ray line. Now the
mass of the heavier of them has to be increased to lie around 250 GeV, while
that of the lighter one remains at 7.1 keV. This requires a new seed mechanism
for the -excess and new Boltzmann equations for the generation of the
DM relic density. All concerned data for RetII and the X-ray line can now be
fitted well and consistency with other indirect limits attained.Comment: 8 eps figures, 1 Table, 7 pages. The paper has been completely
rewritten with additional references and discussions of indirect constraints
from AMS-02 and ANTARES data. Basic results remain unchanged. Version
accepted for publication in Europhysics Letter
Possible explanation of indirect gamma ray signatures from hidden sector fermionic dark matter
We propose the existence of a hidden or dark sector besides the standard
model (SM) of particle physics, whose members (both fermionic and bosonic) obey
a local SU(2) gauge symmetry while behaving like a singlet under the
SM gauge group. However, the fermiomic fields of the dark sector also possess
another global U(1) symmetry which remains unbroken. The local
SU(2) invariance of the dark sector is broken spontaneously when a
scalar field in this sector acquires a vacuum expectation value (VEV) and
thereby generating masses to the dark gauge bosons and dark fermions charged
under the SU(2). The lightest fermion in this dark SU(2)
sector can be a potential dark matter candidate. We first examine the viability
of the model and constrain the model parameter space by theoretical constraints
such as vacuum stability and by the experimental constraints such as PLANCK
limit on relic density, LHC data, limits on spin independent scattering
cross-section from dark matter direct search experiments etc. We then
investigate the gamma rays from the pair annihilation of the proposed dark
matter candidate at the Galactic Centre region. We also extend our calculations
of gamma rays flux for the case of dwarf galaxies and compare the signatures of
gamma rays obtained from these astrophysical sites.Comment: 33 pages, 16 figures, title changed, major revisio
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