896 research outputs found
On the sign of the neutrino asymmetry induced by active-sterile neutrino oscillations in the early Universe
We deal with the problem of the final sign of the neutrino asymmetry
generated by active-sterile neutrino oscillations in the Early Universe solving
the full momentum dependent quantum kinetic equations. We study the parameter
region . For a large
range of values the sign of the neutrino asymmetry is fixed
and does not oscillate. For values of mixing parameters in the region
, the neutrino asymmetry appears to undergo rapid
oscillations during the period where the exponential growth occurs. Our
numerical results indicate that the oscillations are able to change the
neutrino asymmetry sign. The sensitivity of the solutions and in particular of
the final sign of lepton number to small changes in the initial conditions
depends whether the number of oscillations is high enough. It is however not
possible to conclude whether this effect is induced by the presence of a
numerical error or is an intrinsic feature. As the amplitude of the statistical
fluctuations is much lower than the numerical error, our numerical analysis
cannot demonstrate the possibility of a chaotical generation of lepton domains.
In any case this possibility is confined to a special region in the space of
mixing parameters and it cannot spoil the compatibility of the
solution to the neutrino atmospheric data
obtained assuming a small mixing of the with an
neutrino.Comment: Typo's corrected, accepted for publication in Phys.Rev.
Solutions of the atmospheric, solar and LSND neutrino anomalies from TeV scale quark-lepton unification
There is a unique gauge model which
allows quarks and leptons to be unified at the TeV scale. It is already known
that the neutrino masses arise radiatively in the model and are naturally
light. We study the atmospheric, solar and LSND neutrino anomalies within the
framework of this model.Comment: Minor changes, 31 page
Model for a Light Z' Boson
A model of a light boson is constructed and phenomenological bounds are
derived. This boson arises from a very simple extension to the Standard
Model, and it is constrained to be light because the vacuum expectation values
which generate its mass also break the electroweak gauge group. It is difficult
to detect experimentally because it couples exclusively or primarily (depending
on symmetry breaking details) to second and third generation leptons. However,
if the boson is sufficiently light, then there exists the possibility of
the two-body decay occuring. This will provide a
striking signature to test the model.Comment: 20 pages + 5 pages of figures (appended as postscipt files), LaTeX,
OITS-53
Active-Sterile neutrino oscillations and BBN+CMBR constraints
We show how active-sterile neutrino oscillations in the early Universe can
play an interesting role in explaining the current observations of CMBR
anisotropies and light element abundances. We describe different possible
phenomenological scenarios in the interpretation of present data and how
active-sterile neutrino oscillations can provide a viable theoretical
framework.Comment: Some changes, to appear in Phys. Rev.
Mirror matter-type dark matter
There are six main things which any non-baryonic dark matter theory should
endeavour to explain: (1) The basic dark matter particle properties [mass,
stability, darkness]; (2) The similarity in cosmic abundance between ordinary
and non-baryonic dark matter, ; (3) Large scale
structure formation; (4) Microlensing (MACHO) events; (5) Asymptotically flat
rotation curves in spiral galaxies; (6) The impressive DAMA/NaI annual
modulation signal. Only mirror matter-type dark matter is capable of explaining
all six of these desirable features. The purpose of this article is to provide
an up-to-date and pedagogical review of this dark matter candidate.Comment: about 30 page
Static quantities of a neutral bilepton in the 331 model with right-handed neutrinos
A neutral vector boson can possess static electromagnetic properties provided
that the associated field is no self-conjugate. This possibility is explored in
the model with right-handed neutrinos, which
predicts a complex neutral gauge boson in a nontrivial representation of
the electroweak group. In this model the only nonvanishing form factors are the
CP-even ones, which arise from both the quark and gauge sectors, and contribute
to the magnetic dipole and the electric quadrupole moments of this neutral
particle.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Discrete quark-lepton symmetry need not pose a cosmological domain wall problem
Quarks and leptons may be related to each other through a spontaneously
broken discrete symmetry. Models with acceptable and interesting collider
phenomenology have been constructed which incorporate this idea. However, the
standard Hot Big Bang model of cosmology is generally considered to eschew
spontaneously broken discrete symmetries because they often lead to the
formation of unacceptably massive domain walls. We point out that there are a
number of plausible quark-lepton symmetric models which do not produce
cosmologically troublesome domain walls. We also raise what we think are some
interesting questions concerning anomalous discrete symmetries.Comment: 35pp, LATEX, PURD-TH-92-1
Implications of mirror neutrinos for early universe cosmology
The Exact Parity Model (EPM) is, in part, a theory of neutrino mass and
mixing that can solve the atmospheric, solar and LSND anomalies. The central
feature of the neutrino sector is three pairs of maximally mixed ordinary and
mirror neutrinos. It has been shown that ordinary-mirror neutrino oscillations
can generate large neutrino asymmetries in the epoch of the early universe
immediately prior to Big Bang Nucleosynthesis (BBN). The large neutrino
asymmetries generically suppress the production of mirror neutrinos, and a
sufficiently large asymmetry can directly affect light element
synthesis through nuclear reaction rates. In this paper we present a detailed
calculation of neutrino asymmetry evolution driven by the six-flavour EPM
neutrino sector, focusing on implications for BBN.Comment: Latex, about 55 pages long with some figure
Vortex nucleation in Bose-Einstein condensates in an oblate, purely magnetic potential
We have investigated the formation of vortices by rotating the purely
magnetic potential confining a Bose-Einstein condensate. We modified the bias
field of an axially symmetric TOP trap to create an elliptical potential that
rotates in the radial plane. This enabled us to study the conditions for vortex
nucleation over a wide range of eccentricities and rotation rates.Comment: 4 pages 4 figure
Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data
Motivated by the Exact Parity Model and other theories, the hypothesis that
each of the known neutrinos oscillates maximally with a sterile partner has
been put forward as an explanation of the atmospheric and solar neutrino
anomalies. We provide detailed predictions for muon and electron flux ratios
induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric
neutrinos. Several different, carefully chosen cuts on momentum and zenith
angle are proposed, emphasizing the role of up-down flux asymmetries.Comment: LaTeX, 8 figures, 17 pages, version to appear in Phys. Rev. D Rapid
Communication
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