1,194 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.
Experimental implications of mirror matter-type dark matter
Mirror matter-type dark matter is one dark matter candidate which is
particularly well motivated from high energy physics. The theoretical
motivation and experimental evidence are pedagogically reviewed, with emphasis
on the implications of recent orthopositronium experiments, the DAMA/NaI dark
matter search, anomalous meteorite events etc.Comment: about 12 pages lon
Electric Charge Quantization
Experimentally it has been known for a long time that the electric charges of
the observed particles appear to be quantized. An approach to understanding
electric charge quantization that can be used for gauge theories with explicit
factors -- such as the standard model and its variants -- is
pedagogically reviewed and discussed in this article. This approach uses the
allowed invariances of the Lagrangian and their associated anomaly cancellation
equations. We demonstrate that charge may be de-quantized in the
three-generation standard model with massless neutrinos, because differences in
family-lepton--numbers are anomaly-free. We also review the relevant
experimental limits. Our approach to charge quantization suggests that the
minimal standard model should be extended so that family-lepton--number
differences are explicitly broken. We briefly discuss some candidate extensions
(e.g. the minimal standard model augmented by Majorana right-handed neutrinos).Comment: 18 pages, LaTeX, UM-P-92/5
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
An apparatus to search for mirror dark matter via the invisible decay of orthopositronium in vacuum
Mirror matter is a possible dark matter candidate. It is predicted to exist
if parity is an unbroken symmetry of the vacuum. The existence of the mirror
matter, which in addition to gravity is coupled to our world through
photon-mirror photon mixing, would result in orthopositronium (o-Ps) to mirror
orthopositronium (o-Ps') oscillations. The experimental signature of this
effect is the invisible decay of o-Ps in vacuum.
This paper describes the design of the new experiment for a search for the
o-Ps -> invisible decay in vacuum with a sensitivity in the branching ratio of
Br(o-Ps -> invisible)\simeq 10^{-7}, which is an order of magnitude better than
the present limit on this decay mode from the Big Bang Nucleosynthesis. The
experiment is based on a high-efficiency pulsed slow positron beam, which is
also applicable for other experiments with o-Ps, and (with some modifications)
for applied studies. Details of the experimental design and of a new pulsing
method, as well as preliminary results on requirements for the pulsed beam
components are presented. The effects of o-Ps collisions with the cavity walls
as well as the influence of external fields on the o-Ps to o-Ps' oscillation
probability are also discussed.Comment: 28 pages, 8 figure
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.
Electric charge quantization without anomalies?
In gauge theories like the standard model, the electric charges of the
fermions can be heavily constrained from the classical structure of the theory
and from the cancellation of anomalies. We argue that the anomaly conditions
are not quite as well motivated as the classical constraints, since it is
possible that new fermions could exist which cancel potential anomalies. For
this reason we examine the classically allowed electric charges of the known
fermions and we point out that the electric charge of the tau neutrino is
classically allowed to be non-zero. The experimental bound on the electric
charge of the tau neutrino is many orders of magnitude weaker than for any
other known neutrino. We discuss possible modifications of the minimal standard
model such that electric charge is quantized classically.Comment: 10 McGill/93-3
Implications of TeV scale SU(4)xSU(2)_LxSU(2)_R quark-lepton unification
The alternative gauge model, which
allows unification of the quarks and leptons at the TeV scale, is studied in
detail. We discuss the implications for nucleon decay, B and K rare meson
decays and neutrino masses. We also explain how this model solves the gauge
hierarchy problem without using supersymmetry or extra large dimensions.Comment: About 12 pages, 3 eps figs, late
Experimental observation of the 'Tilting Mode' of an array of vortices in a dilute Bose-Einstein Condensate
We have measured the precession frequency of a vortex lattice in a
Bose-Einstein condensate of 87Rb atoms. The observed mode corresponds to a
collective motion in which all the vortices in the array are tilted by a small
angle with respect to the z-axis (the symmetry axis of the trapping potential)
and synchronously rotate about this axis. This motion corresponds to excitation
of a Kelvin wave along the core of each vortex and we have verified that it has
the handedness expected for such helical waves, i.e. precession in the opposite
sense to the rotational flow around the vortices. The experimental method used
to excite this collective mode closely resembles that used to study the
scissors mode and excitation of the scissors mode for a condensate containing a
vortex array was used to determine the angular momentum of the system. Indeed,
the collective tilting of the array that we have observed has previously been
referred to as an `anomalous' scissors mode.Comment: 5 pages, 7 figures to be published in PR
Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models
We re-examine the evolution of neutrino asymmetries in several four neutrino
models. The first case involves the direct creation of by oscillations. In the second case, we consider the mass
hierarchy where oscillations generate a large and some of
this asymmetry is converted into by oscillations. We estimate the implications for BBN for a range of
cosmologically interesting values. The present paper improves on
previous published work by taking into account the finite repopulation rate and
the time dependence of the distortions to the neutrino momentum distributions.
The treatment of chemical decoupling is also improved.Comment: Expanded discussion on the sign of the neutrino asymmetr
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