3,950 research outputs found
The Dark Side of , , Leptogenesis and Inflation in Type-I Seesaw
In the context of the type-I seesaw mechanism, it is known that
is zero and leptogenesis can not be realized if there exists a residual flavor
symmetry resulting in the Tri-Bimaximal neutrino mixing pattern. We propose a
simple framework where additional particles, odd under a symmetry, break
the residual flavor symmetry and the lightest of the odd particles is the
dark matter candidate. As as result, nonzero , ,
leptogenesis and the correct dark matter density can be accommodated. On the
other hand, a odd scalar can play the role of the inflaton with mass of
GeV motivated by the recent BICEP2 results. Interestingly, the model
can "generate" , preferred by the T2K experiment in
the normal hierarchy neutrino mass spectrum.Comment: 23 pages, 8 Figures and 5 Tables. v3: a toy A4 flavor model provided,
version accepted by JHE
On neutrinoless double beta decay in the minimal left-right symmetric model
We analyze the general phenomenology of neutrinoless double beta decay in the
minimal left-right symmetric model. We study under which conditions a New
Physics dominated neutrinoless double beta decay signal can be expected in the
future experiments. We show that the correlation among the different
contributions to the process, which arises from the neutrino mass generation
mechanism, can play a crucial role. We have found that, if no fine tuned
cancellation is involved in the light active neutrino contribution, a New
Physics signal can be expected mainly from the channel. An
interesting exception is the channel which can give a dominant
contribution to the process if the right-handed neutrino spectrum is
hierarchical with MeV and GeV. We also discuss
if a New Physics signal in neutrinoless double beta decay experiments is
compatible with the existence of a successful Dark Matter candidate in the
left-right symmetric models. It turns out that, although it is not a generic
feature of the theory, it is still possible to accommodate such a signal with a
KeV sterile neutrino as Dark matter.Comment: 33 pages, 6 figures, references and complementary constraints added,
version accepted by European Physical Journal
Dark Matter and Lepton Flavour Violation in a Hybrid Neutrino Mass Model
We describe a hybrid model in which the light neutrino mass matrix receives
both tree-level seesaw and loop-induced contributions. An additional U(1) gauge
symmetry is used to stabilize the lightest right-handed neutrino as the Dark
Matter candidate. After fitting the experimental neutrino data, we analyze and
correlate the phenomenological consequences of the model, namely its impact on
electroweak precision measurements, the Dark Matter relic abundance, lepton
flavour violating rare decays and neutrinoless double beta decay. We find that
natural realizations of the model characterized by large Yukawa couplings are
compatible with and close to the current experimental limits.Comment: 25 pages, 9 figures. V2: references added, typos corrected, version
accepted by JHE
Constraining the (Low-Energy) Type-I Seesaw
The type-I seesaw Lagrangian yields a non-generic set of active-sterile
oscillation parameters - the neutrino mass eigenvalues and the physical
elements of the full mixing matrix are entwined. For this reason one is able
to, in principle, test the model by performing enough measurements which are
sensitive to neutrino masses and lepton mixing. We point out that for light
enough right-handed neutrino masses - less than 10 eV - next-generation
short-baseline neutrino oscillation experiments may be able to unambiguously
rule out (or "rule in") the low energy seesaw as the Lagrangian that describes
neutrino masses. These types of searches are already under consideration in
order to address the many anomalies from accelerator neutrino experiments
(LSND, MiniBooNe), reactor neutrino experiments (the "reactor anomaly") and
others. In order to test the low-energy seesaw, it is crucial to explore
different oscillation channels, including nu_e and nu_mu disappearance and
nu_mu to nu_tau appearance.Comment: 15 pages, five figure
Polarized gamma rays from dark matter annihilations
In this paper, we explore the possibility of a linearly polarized gamma-ray
signal from dark matter annihilations in the Galactic center. Considering
neutral weakly interacting massive particles, a polarized gamma-ray signal can
be realized by a two-component dark matter model of Majorana fermions with an
anapole moment. We discuss the spin alignment of such dark matter fermions in
the Galactic center and then estimate the intensity and the polarizability of
the final-state electromagnetic radiation in the dark matter annihilations. For
low-mass dark matter, the photon flux at sub-GeV energies may be polarized at a
level detectable in current X-ray polarimeters. Depending on the mass ratio
between the final-state fermion and DM, the degree of polarization at the mass
threshold can reach or even higher, providing us with a new tool for
probing the nature of dark matter in future gamma-ray polarization experiments.Comment: 19 pages, 7 figures. v2: version accepted by Physics Letters
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