10,565 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
A Deep Optical Observation for an Enigmatic Unidentified Gamma-Ray Source 3EG J1835+5918
We report a deep optical imaging observation by the Subaru telescope for a
very soft X-ray source RX J1836.2+5925, which has been suspected to be an
isolated neutron star associated with the brightest as-yet unidentified EGRET
source outside the Galactic plane, 3EG J1835+5918. An extended source having a
complex, bipolar shape is found at B ~ 26, and this might be an extended pulsar
nebular whose flux is about 5-6 orders of magnitude lower than gamma-ray flux,
although finding a galaxy of this magnitude by chance in the error circle is of
order unity. We have found two even fainter, possibly point sources at B ~ 28,
although their detections are not firm because of low signal-to-noise. If the
extended object of B ~ 26 is a galaxy and not related to 3EG J1835+5918, a
lower limit on X-ray/optical flux ratio is set as f_X/f_B >~ 2700, giving a
further strong support of the neutron-star identification of 3EG J1835+5918.
Interestingly, if either of the two sources at B ~ 28 is the real counterpart
of RX J1836.2+5925 and thermal emission from the surface of an isolated neutron
star, the temperature and distance to the source become ~ 4 x 10^5K and ~300pc,
respectively, showing a striking similarity of its spectral energy distribution
to the proto-type radio-quiet gamma-ray pulsar Geminga. No detection of
nonthermal hard X-ray emission is consistent with the ASCA upper limit, if the
nonthermal flux of 3EG J1835+5918/RX J1836.2+5925 is at a similar level with
that of Gemiga.Comment: PASJ Letters in press. (Received March 26; Accepted May 17
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