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

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 $\sim 10^{50}$ 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

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.

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

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/

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 $\mu$, 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

Brans-Dicke model constrained from Big Bang nucleosynthesis and magnitude redshift relations of Supernovae

The Brans-Dicke model with a variable cosmological term ($BD\Lambda$) has been investigated with use of the coupling constant of $\omega=10^4$. Parameters inherent in this model are constrained from comparison between Big Bang nucleosynthesis and the observed abundances. Furthermore, the magnitude redshift ($m-z$) relations are studied for $BD\Lambda$ with and without another constant cosmological term in a flat universe. Observational data of Type Ia Supernovae are used in the redshift range of $0.01<z<2$. 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 $m-z$ relation.Comment: Submitted to A&A, 4 pages, 3 figure

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 $[SU(2)\times U(1)]'$, with the breaking scale larger by about factor of 30 than the scale of the standard $SU(2)\times U(1)$ 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 $\bar L=L_e+L_\mu-L_\tau$, 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

Peaks above the Harrison-Zel'dovich spectrum due to the Quark-Gluon to Hadron Transition

The quark-gluon to hadron transition affects the evolution of cosmological perturbations. If the phase transition is first order, the sound speed vanishes during the transition, and density perturbations fall freely. This distorts the primordial Harrison-Zel'dovich spectrum of density fluctuations below the Hubble scale at the transition. Peaks are produced, which grow at most linearly in wavenumber, both for the hadron-photon-lepton fluid and for cold dark matter. For cold dark matter which is kinetically decoupled well before the QCD transition clumps of masses below $10^{-10} M_\odot$ are produced.Comment: Extended version, including evolution of density perturbations for a bag model and for a lattice QCD fit (3 new figures). Spectrum for bag model (old figure) is available in astro-ph/9611186. 9 pages RevTeX, uses epsf.sty, 3 PS figure