8 research outputs found
Electromagnetic Cascades and Cascade Nucleosynthesis in the Early Universe
We describe a calculation of electromagnetic cascading in radiation and
matter in the early universe initiated by the decay of massive particles or by
some other process. We have used a combination of Monte Carlo and numerical
techniques which enables us to use exact cross sections, where known, for all
the relevant processes. In cascades initiated after the epoch of big bang
nucleosynthesis -rays in the cascades will photodisintegrate He,
producing He and deuterium. Using the observed He and deuterium
abundances we are able to place constraints on the cascade energy deposition as
a function of cosmic time. In the case of the decay of massive primordial
particles, we place limits on the density of massive primordial particles as a
function of their mean decay time, and on the expected intensity of decay
neutrinos.Comment: compressed and uuencoded postscript. We now include a comparison with
previous work of the photon spectrum in the cascade and the limits we
calculate for the density of massive particles. The method of calculation of
photon spectra at low energies has been improved. Most figures are revised.
Our conclusions are substantially unchange
A built-in scale in the initial spectrum of density perturbations: evidence from cluster and CMB data
We calculate temperature anisotropies of the cosmic microwave background
(CMB) for several initial power spectra of density perturbations with a
built-in scale suggested by recent optical data on the spatial distribution of
rich clusters of galaxies. Using cosmological models with different values of
spectral index, baryon fraction, Hubble constant and cosmological constant, we
compare the calculated radiation power spectrum with the CMB temperature
anisotropies measured by the Saskatoon experiment. We show that spectra with a
sharp peak at 120 h^{-1} Mpc are in agreement with the Saskatoon data. The
combined evidence from cluster and CMB data favours the presence of a peak and
a subsequent break in the initial matter power spectrum. Such feature is
similar to the prediction of an inflationary model where an inflaton field is
evolving through a kink in the potential.Comment: LaTex style, 9 pages, 3 PostScript figures embedded, accepted by J.
Exper. Theor. Phy
Eternal annihilations of light photinos
In a class of low-energy supersymmetry models the photino is a natural dark
matter candidate. We investigate the effects of post-freeze-out photino
annihilations which can generate electromognetic cascades and lead to
photo-destruction of He and subsequent overproduction of D and He. We
also generalize our analysis to a generic dark matter component whose relic
abundance is {\it not} determined by the cross section of the
self-annihilations giving rise to electromagnetic showers.Comment: 13 page LaTeX file (no figures
Three Neutrino scales and Singular Seesaw Mechanism
It is shown that the singular seesaw mechanism can simultaneously explain all
the existing data supporting nonzero neutrino masses and mixing. The three
mass-squared differences that are needed to accommodate the atmospheric
neutrino data (through oscillation), the solar neutrino data
via MSW mechanism (through oscillation), and the positive
result of oscillation from LSND can be generated by this
mechanism, whereas the vacuum oscillation solution to the solar neutrino
problem is disfavored. We find that the electron and tau neutrino masses are of
order eV, and the muon neutrino and a sterile neutrino are almost
maximally mixed to give a mass of order 1 eV. Two heavy sterile neutrinos have
a mass of order 1 keV which can be obtained by the double seesaw mechanism with
an intermediate mass scale GeV. A possible origin of such a scale
is discussed.Comment: Revtex, 7 pages with 1 epsfig (uuencoded
Supernova Bounds on Resonant Active-Sterile Neutrino Conversions
We discuss the effects of resonant and ( is a sterile neutrino) conversions in the dense medium of
a supernova. In particular, we assume the sterile neutrino to be in the
hot dark matter few eV mass range. The implications of such a scenario for the
supernova shock re-heating, the detected signal from SN1987A and
for the r-process nucleosynthesis hypothesis are analysed in some detail. The
resulting constraints on mixing and mass difference for the
system are derived. There is also an allowed region in the neutrino parameter
space for which the r-process nucleosynthesis can be enhanced.Comment: Latex file, 27 pages including 10 ps figures, uses psfig.sty. Few
references added, some change in the Acknowledgements and some minor
corrections in the tex