612 research outputs found
Perturbative approach for mass varying neutrinos coupled to the dark sector in the generalized Chaplygin gas scenario
We suggest a perturbative approach for generic choices for the universe
equation of state and introduce a novel framework for studying mass varying
neutrinos (MaVaN's) coupled to the dark sector. For concreteness, we examine
the coupling between neutrinos and the underlying scalar field associated with
the generalized Chaplygin gas (GCG), a unification model for dark energy and
dark matter. It is shown that the application of a perturbative approach to
MaVaN mechanisms translates into a constraint on the coefficient of a linear
perturbation, which depends on the ratio between a neutrino energy dependent
term and scalar field potential terms. We quantify the effects on the MaVaN
sector by considering neutrino masses generated by the seesaw mechanism. After
setting the GCG parameters in agreement with general cosmological constraints,
we find that the squared speed of sound in the neutrino-scalar GCG fluid is
naturally positive. In this scenario, the model stability depends on previously
set up parameters associated with the equation of state of the universe. Our
results suggest that the GCG is a particularly suitable candidate for
constructing a stable MaVaN scenario.Comment: 27 pages, 9 figure
Natural model with an inverse seesaw and leptonic dark matter
We consider a model for a Z'-boson coupled only to baryon minus lepton number
and hypercharge. Besides the usual right-handed neutrinos, we add a pair of
fermions with a fractional lepton charge, which we therefore call leptinos. One
of the leptinos is taken to be odd under an additional Z_2 charge, the other
even. This allows for a natural (inverse) seesaw mechanism for neutrino masses.
The odd leptino is a candidate for dark matter, but has to be resonantly
annihilated by the Z'-boson or the Higgs-boson responsible for giving mass to
the former. Considering collider and cosmological bounds on the model, we find
that the Z'-boson and/or the extra Higgs-boson can be seen at the LHC. With
more pairs of leptinos leptogenesis is possible.Comment: 29 pages, 9 figures. RGE section moved to appendix and other minor
corrections applied to matched published versio
Affleck-Dine leptogenesis via multiscalar evolution in a supersymmetric seesaw model
A leptogenesis scenario in a supersymmetric standard model extended with
introducing right-handed neutrinos is reconsidered. Lepton asymmetry is
produced in the condensate of a right-handed sneutrino via the Affleck-Dine
mechanism. The LH_u direction develops large value due to a negative effective
mass induced by the right-handed sneutrino condensate through the Yukawa
coupling of the right-handed neutrino, even if the minimum during the inflation
is fixed at the origin. The lepton asymmetry is nonperturbatively transfered to
the LH_u direction by this Yukawa coupling.Comment: 19 pages, 3 figures. Revised version for publication. The model was
modified to fix some problem
Electron to Muon Conversion in Low-Energy Electron-Nucleus Scattering
We present an estimate of the electron to muon conversion cross section in
fixed-target elastic electron scattering. The matrix element is calculated analytically in two scenarios
introducing suitable approximations. We consider on the one hand side the case
of three light Dirac neutrinos with CKM-type leptonic mixing and on the other
hand a typical see-saw scenario. We evaluate the coulombic contribution to the
scattering cross section in the limit of vanishing energy transfer to the
nucleus and, thus, obtain a realistic estimate for the total conversion cross
section. Although we find that in the see-saw scenario the cross section can be
enhanced by as much as twenty orders of magnitude in comparison to the Dirac
case, it is still not experimentally accessible.Comment: 9 pages, 1 figur
Inflation in minimal left-right symmetric model with spontaneous D-parity breaking
We present a simplest inflationary scenario in the minimal left-right
symmetric model with spontaneous D-parity breaking, which is a well motivated
particle physics model for neutrino masses. This leads us to connect the
observed anisotropies in the cosmic microwave background to the sub-eV neutrino
masses. The baryon asymmetry via the leptogenesis route is also discussed
briefly.Comment: (v1) 4 pages, 1 figure; (v2) typos corrected; (v3) title and abstract
changed, numerical estimates given, minor changes; (v4) 5 pages, relations
between the neutrino masses and the CMB fluctuations become more explicit,
miscellaneous changes, to appear in Physical Review
Constraining Nonstandard Neutrino-Electron Interactions
We present a detailed analysis on nonstandard neutrino interactions (NSI)
with electrons including all muon and electron (anti)-neutrino data from
existing accelerators and reactors, in conjunction with the ``neutrino
counting'' data (e- e+ -> nu nu gamma) from the four LEP collaborations. First
we perform a one-parameter-at-a-time analysis, showing how most constraints
improve with respect to previous results reported in the literature. We also
present more robust results where the NSI parameters are allowed to vary freely
in the analysis. We show the importance of combining LEP data with the other
experiments in removing degeneracies in the global analysis constraining
flavor-conserving NSI parameters which, at 90 % and 95 % C.L., must lie within
unique allowed regions. Despite such improved constraints, there is still
substantial room for improvement, posing a big challenge for upcoming
experiments.Comment: 19 pages, 4 figures. Final version to appear in Phys. Rev.
Hard-Thermal-Loop Corrections in Leptogenesis I: CP-Asymmetries
We investigate hard-thermal-loop (HTL) corrections to the CP-asymmetries in
neutrino and, at high temperature, Higgs boson decays in leptogenesis. We pay
special attention to the two leptonic quasiparticles that arise at non-zero
temperature and find that there are four contributions to the CP-asymmetries,
which correspond to the four combinations of the two leptonic quasiparticles in
the loop and in the final states. In two additional cases, we approximate the
full HTL-lepton propagator with a zero-temperature propagator that employs the
thermal lepton mass m_l(T), or the asymptotic thermal lepton mass sqrt{2}
m_l(T). We find that the CP-asymmetries in the one-mode approaches differ by up
to one order of magnitude from the full two-mode treatment in the interesting
temperature regime T \sim M_1. The asymmetry in Higgs boson decays turns out to
be two orders of magnitude larger than the asymmetry in neutrino decays in the
zero-temperature treatment. The effect of HTL corrections on the final lepton
asymmetry are investigated in paper II of this series.Comment: 38 pages, 14 figure
New Ambiguity in Probing CP Violation in Neutrino Oscillations
If neutrinos get mass via the seesaw mechanism the mixing matrix describing neutrino oscillations can be effectively nonunitary. We show that in this case the neutrino appearance probabilities involve a new CP phase ϕ associated with nonunitarity. This leads to an ambiguity in extracting the "standard" three-neutrino phase δCP, which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of δCP
The importance of flavor in leptogenesis
We study leptogenesis from the out-of-equilibrium decays of the lightest
heavy neutrino in the medium (low) temperature regime, T\lsim 10^{12}
GeV ( GeV), where the rates of processes mediated by the (and
) Yukawa coupling are non negligible, implying that the effects of lepton
flavors must be taken into account. We find important quantitative and
qualitative differences with respect to the case where flavor effects are
ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of
magnitude; (ii) The sign of the asymmetry can be opposite to what one would
predict from the sign of the total lepton asymmetry ; (iii)
Successful leptogenesis is possible even with .Comment: 27 pages, 2 figures. Added 3 reference
Viable Supersymmetry and Leptogenesis with Anomaly Mediation
The seesaw mechanism that explains the small neutrino masses comes naturally
with supersymmetric (SUSY) grand unification and leptogenesis. However, the
framework suffers from the SUSY flavor and CP problems, and has a severe
cosmological gravitino problem. We propose anomaly mediation as a simple
solution to all these problems, which is viable once supplemented by the
D-terms for U(1)_Y and U(1)_{B-L}. Even though the right-handed neutrino mass
explicitly breaks U(1)_{B-L} and hence reintroduces the flavor problem, we show
that it lacks the logarithmic enhancement and poses no threat to the framework.
The thermal leptogenesis is then made easily consistent with the gravitino
constraint.Comment: 5 pages, one figure, uses Revtex4; Discussion on the upper bound on
the LSP mass added. The version published in PR
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