19 research outputs found
An improved cosmological bound on the tau-neutrino mass
We consider the influence of non-equilibrium electronic neutrinos (and
anti-neutrinos) on the neutron-to-proton ratio. These neutrinos would come from
massive annihilations . For sufficiently large masses this new effect would strongly
enhance the (n/p)-ratio, leading to a very stringent bound on the
mass, even adopting a rather weak upper bound on the effective number on
neutrino species during nucleosynthesis.Comment: 10 pages, LaTex file + 1 figure compressed using uufile
Impact of massive tau-neutrinos on primordial nucleosynthesis. Exact calculations
The influence of a massive Majorana tau-neutrino on primordial
nucleosynthesis is rigorously calculated. The system of three
integro-differential kinetic equations is solved numerically for the
tau-neutrino mass in the interval from 0 to 20 MeV. It is found that the usual
assumption of kinetic equilibrium is strongly violated and non-equilibrium
corrections considerably amplify the effect. Even a very weak restriction from
nucleosynthesis, allowing for one extra massless neutrino species, permits to
conclude that m_\nu_\tau < 1 MeV. For a stricter bound, e.g. for dN < 0.3, the
limit is m_\nu_\tau < 0.35 MeV.Comment: 30 pages, 9 figures, 2 tables, revised figures, minor change
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
Recent Results on Neutrino Masses
I review the main options one has of introducing mass to neutrinos, including
broken R-parity models, as well as the constraints on neutrino properties that
follow from astrophysics, cosmology as well as laboratory observations.Comment: 13 pages. Latex. 10 figures. Invited talk, Erice, Italy, September
1997. Size corrected. e-mail address adde
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
Supersymmetric Dark Matter
There is almost universal agreement among astronomers that most of the mass
in the Universe and most of the mass in the Galactic halo is dark. Many lines
of reasoning suggest that the dark matter consists of some new, as yet
undiscovered, weakly-interacting massive particle (WIMP). There is now a vast
experimental effort being surmounted to detect WIMPS in the halo. The most
promising techniques involve direct detection in low-background laboratory
detectors and indirect detection through observation of energetic neutrinos
from annihilation of WIMPs that have accumulated in the Sun and/or the Earth.
Of the many WIMP candidates, perhaps the best motivated and certainly the most
theoretically developed is the neutralino, the lightest superpartner in many
supersymmetric theories. We review the minimal supersymmetric extension of the
Standard Model and discuss prospects for detection of neutralino dark matter.
We review in detail how to calculate the cosmological abundance of the
neutralino and the event rates for both direct- and indirect-detection schemes,
and we discuss astrophysical and laboratory constraints on supersymmetric
models. We isolate and clarify the uncertainties from particle physics, nuclear
physics, and astrophysics that enter at each step in the calculation. We
briefly review other related dark-matter candidates and detection techniques.Comment: The complete postscript file is available at
ftp://ftp.npac.syr.edu/pub/users/jungman/susyreview/susyreview.ps.Z The TeX
source and figures (plain TeX; macros included) are at
ftp://ftp.npac.syr.edu/pub/users/jungman/susyreview/susyreview.tar.Z Full
paper NOT submitted to lanl archive: table of contents only. To appear in
Physics Report
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
Neutrinos and physics beyond the standard model
A brief sketch is made of the present observational status of neutrino physics, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as cosmological data on the amplitude of primordial density fluctuations. I also briefly review the ways to account for the observed anomalies and some of their implications
Neutrinos Properties Beyond the Standard Model
The present observational status of neutrino physics is sketched, with
emphasis on the hints that follow from solar and atmospheric neutrino
observations, as well as dark matter. I also briefly review the ways to account
for the observed anomalies and some of their implicationsComment: 14 pages. Latex. 12 figures. Plenary talk, WIN97, Capri, Italy, June
1997. Minor changes, references and acknowledgements adde