10,600 research outputs found
Electromagnetic Cascade in the Early Universe and its Application to the Big-Bang Nucleosynthesis
We investigate the electromagnetic cascade initiated by injection of very
high energy photons in the early Universe and calculate the cascade spectrum by
solving a set of Boltzmann equations numerically. In the calculation we take
account of Compton scattering off the background electrons and pair creation
off the background nucleons as well as photon-photon processes and inverse
Compton scattering. We also apply our cascade spectrum to the big bang
nucleosynthesis with photo-dissociation processes due to heavy unstable
particles and obtain the constraint on their lifetime and abundance.Comment: 21pages (compressed and uuencoded postscript file including 6
figures
511 keV Gamma Ray from Moduli Decay in the Galactic Bulge
We show that the decay of a light scalar boson of mass 1-10 MeV may
account for the fluxes of 511 keV gamma ray observed by SPI/INTEGRAL. We argue
that candidates of such a light scalar boson is one of the string moduli or a
scalar partner of the axion in a supersymmetric theory.Comment: 6 pages, no figure, we have added an appendix to describe the
dilution of the moduli by the thermal inflation and some minor correction
Gravitino Production in the Inflationary Universe and the Effects on Big-Bang Nucleosynthesis
Gravitino production and decay in the inflationary universe are reexamined.
Assuming that the gravitino mainly decays into a photon and a photino, we
calculate the upperbound on the reheating temperature. Compared to previous
works, we have essentially improved the following two points: (i) the helicity
gravitino production cross sections are calculated by using
the full relevant terms in the supergravity lagrangian, and (ii) the high
energy photon spectrum is obtained by solving the Boltzmann equations
numerically. Photo-dissociation of the light elements (D, T, He, He)
leads to the most stringent upperbound on the reheating temperature, which is
given by (--)GeV for the gravitino mass 100GeV--1TeV. On the
other hand, requiring that the present mass density of photino should be
smaller than the critical density, we find that the reheating temperature have
to be smaller than (--)GeV for the photino mass (10--100)GeV,
irrespectively of the gravitino mass. The effect of other decay channels is
also considered
Double inflation in supergravity and the primordial black hole formation
We study a double inflation model (a hybrid inflation + a new inflation) in
supergravity and discuss the formation of primordial black holes (PBHs) with
mass \sim 10^{-20}-10^{5}M_{\odot}. We find that in a wide range of parameter
space, we obtain PBHs which amount to \Omega \simeq 1, i.e., PBH dark matter.
Also, we find a set of inflation parameters which produces PBHs evaporating
now. Those PBHs may be responsible for antiproton fluxes observed by the BESS
experiment.Comment: 14 pages, 2 figures (RevTeX file
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