852 research outputs found
Baryogenesis from Symmetry Principle
In this work, a formalism based on symmetry which allows one to express
asymmetries of all the particles in terms of conserved charges is developed.
The manifestation of symmetry allows one to easily determine the viability of a
baryogenesis scenario and also to identity the different roles played by the
symmetry. This formalism is then applied to the standard model and its
supersymmetric extension, which constitute two important foundations for
constructing models of baryogenesis.Comment: 15 pages, 1 figure, 3 tables. Slight modifications to match the
published versio
The EDGES signal: An imprint from the mirror world?
Recent results from the Experiment to Detect the Global Epoch of Reionization
Signature (EDGES) show an anomalous spectral feature at redshifts
in its 21-cm absorption signal. This deviation from cosmological predictions
can be understood as a consequence of physics that either lower the hydrogen
spin temperature or increases the radiation temperature through the injection
of soft photons in the bath. In the latter case, standard model neutrino decays
induced by effective magnetic and electric transition
moments () are precluded by the tight astrophysical constraints
on . We show that if mirror neutrinos are present in the bath
at early times, an analogous mechanism in the mirror sector can lead to a
population of mirror photons that are then "processed" into visible photons
through resonant conversion, thus accounting for the EDGES signal. We point out
that the mechanism can work for mirror neutrinos which are either heavier than
or degenerate with the standard model (SM) neutrinos, a scenario naturally
realized in mirror twin Higgs models.Comment: 8 pages, 2 figure
Flavoured Soft Leptogenesis
We study the impact of flavour in ``soft leptogenesis'' (leptogenesis induced
by soft supersymmetry breaking terms). We address the question of how flavour
effects can affect the region of parameters in which successful soft
leptogenesis induced by CP violation in the right-handed sneutrino mixing is
possible. We find that for decays which occur in the intermediate to strong
washout regimes for all flavours, the produced total asymmetry can be up
to a factor larger than the one predicted with flavour effects
being neglected. This enhancement, permits slightly larger values of the
required lepton violating soft bilinear term.Comment: 20 pages, 5 figures. Version accepted in JHEP. Results unchange
Non-unitary evolution of neutrinos in matter and the leptonic unitarity test
We present a comprehensive study of the three-active plus sterile
neutrino model as a framework for constraining leptonic unitarity violation
induced at energy scales much lower than the electroweak scale. We formulate a
perturbation theory with expansion in small unitarity violating matrix element
while keeping (non- suppressed) matter effect to all orders. We show
that under the same condition of sterile state masses as in vacuum, assuming typical
accelerator based long-baseline neutrino oscillation experiment, one can derive
a very simple form of the oscillation probability which consists only of
zeroth-order terms with the unique exception of probability leaking term
of . We argue, based on our
explicit computation to fourth-order in , that all the other terms are
negligibly small after taking into account the suppression due to the mass
condition for sterile states, rendering the oscillation probability {\em
sterile-sector model independent}. Then, we identify a limited energy region in
which this suppression is evaded and the effects of order corrections may
be observable. Its detection would provide another way, in addition to
detecting , to distinguish between low-scale and
high-scale unitarity violation. We also solve analytically the zeroth-order
system in matter with uniform density to provide a basis for numerical
evaluation of non-unitary neutrino evolution.Comment: 35 content pages + 12 appendix pages, 4 figures; Several clarifying
modifications to match the published versio
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