231 research outputs found
Neutrino Balls and Gamma-Ray Bursts
We propose a mechanism by which the neutrino emission from a supernova-type
explosion can be converted into a gamma-ray burst of total energy ergs. This occurs naturally if the explosion is situated inside a ball
of trapped neutrinos, which in turn may lie at a galactic core. There are
possible unique signatures of this scenario.Comment: Tex, 12 pages, no figures, CITA/93/2
The astrophysical reaction 8Li(n,gamma)9Li from measurements by reverse kinematics
We study the breakup of 9Li projectiles in high energy (28.5 MeV/u)
collisions with heavy nuclear targets (208Pb). The wave functions are
calculated using a single-particle model for 9Li, and a simple optical
potential model for the scattering part. A good agreement with measured data is
obtained with insignificant E2 contribution.Comment: 4 pages, 3 figure
Coulomb dissociation of 9Li and the rate of the 8Li(n,g)9Li reaction
We calculate the Coulomb dissociation of 9Li on Pb and U targets at 28.5
MeV/A beam energy within a finite range distorted wave Born approximation
formalism of the breakup reactions. Invoking the principle of detailed balance,
these cross sections are used to determine the excitation function and
subsequently the rate of the radiative capture reaction 8Li(n,g)9Li at
astrophysical energies. Our method is free from the uncertainties associated
with the multipole strength distributions of the 9Li nucleus. The rate of this
reaction at a temperature of 10^9K is found to be about 2900 cm^3 mole^{-1}
s^{-1}.Comment: 13 pages Revtex, 2 figures, title and abstract changed on referee's
suggestions, figures modified and discussions extended, results remain the
same; version to appear in Phys. Rev.
Protecting Classical-Quantum Signals in Free Space Optical Channels
Due to turbulence and tracking errors, free-space optical channels involving
mobile transceivers are characterized by a signal's partial loss or complete
erasure. This work presents an error correction protocol capable of protecting
a signal passing through such channels by encoding it with an ancillary
entangled bipartite state. Beyond its ability to offer protection under
realistic channel conditions, novel to our protocol is its ability to encompass
both classical and quantum information on the encoded signal. We show how,
relative to non-encoded direct transmission, the protocol can improve the
fidelity of transmitted coherent states over a wide range of losses and erasure
probabilities. In addition, the use of ancillary non-Gaussian entangled
bipartite states in the signal encoding is considered, showing how this can
increase performance. Finally, we briefly discuss the application of our
protocol to the transmission of more complex input states, such as multi-mode
entangled states
Neutrino-Lasing in The Early Universe
Recently, Madsen has argued that relativistic decays of massive neutrinos
into lighter fermions and bosons may lead, via thermalization, to the formation
of a Bose condensate. If correct, this could generate mixed hot and cold dark
matter, with important consequences for structure formation.
From a detailed study of such decays, we arrive at substantially different
conclusions; for a wide range of masses and decay times, we find that
stimulated emission of bosons dominates the decay. This phenomenon can best be
described as a neutrino laser, pumped by the QCD phase transition. We discuss
the implications for structure formation and the dark-matter problem.Comment: 7 pages, 3 figures included as uuencoded file, CITA/93/
Superconducting Cosmic Strings and Primordial Nucleosynthesis
We show that the presence of superconducting cosmic strings in the early Universe may have dramatic consequences for primordial nucleosynthesis. Due to the enormous currents that they potentially can carry, very large magnetic fields can be produced in the vicinity of such strings. As they then move through the primordial plasma, charged particles are deflected away by the magnetic pressure surrounding the strings. We show that the predicted primordial abundances can differ radically from standard big-bang predictions, and may even be consistent with an Ωb=1 universe
Cosmic Strings in an Open Universe with Baryonic and Non-Baryonic Dark Matter
We study the effects of cosmic strings on structure formation in open
universes. We calculate the power spectrum of density perturbations for two
class of models: one in which all the dark matter is non baryonic (CDM) and one
in which it is all baryonic (BDM). Our results are compared to the 1 in 6 IRAS
QDOT power spectrum. The best candidates are then used to estimate , the
energy per unit length of the string network. Some comments are made on
mechanisms by which structures are formed in the two theories.Comment: uu-encoded compressed tar of postscript files, Imperial/TP/94-95/0
Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos
We suggest that recent neutrino puzzles that are the solar and atmospheric
neutrino deficits as well as the possible neutrino oscillations reported by the
LSND experiment and the possibility of massive neutrinos providing the hot
component of the cosmological dark matter, can all be naturally explained by
assuming existence of a mirror world described by an ``electroweak'' gauge
symmetry , with the breaking scale larger by about factor
of 30 than the scale of the standard model. An interesting
aspect of this model is that the sterile neutrinos arise from the hidden mirror
sector of the theory and thus their lightness is more natural than in the usual
neutrino mass scenarios. The needed pattern of the neutrino mass matrix in this
model is obtained by assuming a conserved ZKM-type global lepton number , which is violated by Planck scale effects. One implication
of our proposal is that bulk of the dark matter in the universe is a warm dark
matter consisting of few KeV mass particles rather than the 100 GeV range
particles of the currently popular cold dark matter scenarios.Comment: 10 pages, Latex, no figure
Brans-Dicke model constrained from Big Bang nucleosynthesis and magnitude redshift relations of Supernovae
The Brans-Dicke model with a variable cosmological term () has
been investigated with use of the coupling constant of .
Parameters inherent in this model are constrained from comparison between Big
Bang nucleosynthesis and the observed abundances. Furthermore, the magnitude
redshift () relations are studied for with and without another
constant cosmological term in a flat universe. Observational data of Type Ia
Supernovae are used in the redshift range of . It is found that our
model with energy density of the constant cosmological term with the value of
0.7 can explain the SNIa observations, though the model parameters are
insensitive to the relation.Comment: Submitted to A&A, 4 pages, 3 figure
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