537 research outputs found
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
Maximum lepton asymmetry from active-sterile neutrino oscillations in the Early Universe
A large lepton asymmetry could be generated in the Early Universe by
oscillations of active to sterile neutrinos with a small mixing angle sin 2
\theta < 10^-2. The final order of magnitude of the lepton asymmetry \eta is
mainly determined by its growth in the last stage of evolution when the MSW
resonance dominates the kinetic equations. In this paper we present a simple
way of calculating the maximum possible lepton asymmetry which can be created.
Our results are in good agreement to previous calculations. Furthermore, we
find that the growth of asymmetry does not obey any particular power law. We
find that the maximum possible asymmetry at the freeze-out of the n/p ratio at
T \sim 1 MeV strongly depends on the mass-squared difference \delta m^2: the
asymmetry is negligible for \delta m^2 \ll 1 eV^2 and reaches asymptotically
large values for \delta m^2 \ge 50 eV^2.Comment: 14 pp, 4 figure
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
Mirror World and its Cosmological Consequences
We briefly review the concept of a parallel `mirror' world which has the same
particle physics as the observable world and couples to the latter by gravity
and perhaps other very weak forces. The nucleosynthesis bounds demand that the
mirror world should have a smaller temperature than the ordinary one. By this
reason its evolution should substantially deviate from the standard cosmology
as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are
concerned. In particular, we show that in the context of certain baryogenesis
scenarios, the baryon asymmetry in the mirror world should be larger than in
the observable one. Moreover, we show that mirror baryons could naturally
constitute the dominant dark matter component of the Universe, and discuss its
cosmological implications
Explaining through the synthesis of ordinary matter from mirror matter: a more general analysis
The emerging cosmological picture is of a spatially flat universe composed
predominantly of three components: ordinary baryons (),
non-baryonic dark matter () and dark energy
(). We recently proposed that ordinary matter was
synthesised from mirror matter, motivated by the argument that the observed
similarity of and suggests an underlying similarity
between the fundamental properties of ordinary and dark matter particles. In
this paper we generalise the previous analysis by considering a wider class of
effective operators that non-gravitationally couple the ordinary and mirror
sectors. We find that while all considered operators imply
few, only a subset quantitatively reproduce the observed ratio
. The eV mass scale induced
through these operators hints at a connection with neutrino oscillation
physics.Comment: minor changes, some references added, about 10 page
Neutrino physics and the mirror world: how exact parity symmetry explains the solar neutrino deficit, the atmospheric neutrino anomaly and the LSND experiment
Evidence for oscillations has been
reported at LAMPF using the LSND detector. Further evidence for neutrino mixing
comes from the solar neutrino deficit and the atmospheric neutrino anomaly. All
of these anomalies require new physics. We show that all of these anomalies can
be explained if the standard model is enlarged so that an unbroken parity
symmetry can be defined. This explanation holds independently of the actual
model for neutrino masses. Thus, we argue that parity symmetry is not only a
beautiful candidate for a symmetry beyond the standard model, but it can also
explain the known neutrino physics anomalies.Comment: 27 pages, LaTeX, no figures, additional discussion on big bang
nucleosynthesis, some additional references, to appear in Phys. Rev.
Quasi-2D Confinement of a BEC in a Combined Optical and Magnetic Potential
We have added an optical potential to a conventional Time-averaged Orbiting
Potential (TOP) trap to create a highly anisotropic hybrid trap for ultracold
atoms. Axial confinement is provided by the optical potential; the maximum
frequency currently obtainable in this direction is 2.2 kHz for rubidium. The
radial confinement is independently controlled by the magnetic trap and can be
a factor of 700 times smaller than in the axial direction. This large
anisotropy is more than sufficient to confine condensates with ~10^5 atoms in a
Quasi-2D (Q2D) regime, and we have verified this by measuring a change in the
free expansion of the condensate; our results agree with a variational model.Comment: 11 pages, 10 figur
Comparing and contrasting the and solutions to the atmospheric neutrino problem with SuperKamiokande data
The and solutions to the
atmospheric neutrino problem are compared with SuperKamiokande data. The
differences between these solutions due to matter effects in the Earth are
calculated for the ratio of -like to -like events and for up-down flux
asymmetries. These quantities are chosen because they are relatively
insensitive to theoretical uncertainties in the overall neutrino flux
normalisation and detection cross-sections and efficiencies. A
analysis using these quantities is performed yielding ranges which
are approximately given by and for
for the and solutions, respectively. Values of smaller than about
eV are disfavoured for the
solution, suggesting that future long baseline experiments should see a
positive signal if this scenario is the correct one.Comment: revtex, 22 pages, 12 figure
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
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
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