35 research outputs found
High Temperature Matter and Gamma Ray Spectra from Microscopic Black Holes
The relativistic viscous fluid equations describing the outflow of high
temperature matter created via Hawking radiation from microscopic black holes
are solved numerically for a realistic equation of state. We focus on black
holes with initial temperatures greater than 100 GeV and lifetimes less than 6
days. The spectra of direct photons and photons from decay are
calculated for energies greater than 1 GeV. We calculate the diffuse gamma ray
spectrum from black holes distributed in our galactic halo. However, the most
promising route for their observation is to search for point sources emitting
gamma rays of ever-increasing energy.Comment: 33 pages, 13 figures, to be submitted to PR
Calculation of the emergent spectrum and observation of primordial black holes
We calculate the emergent spectrum of microscopic black holes, which emit
copious amounts of thermal ``Hawking'' radiation, taking into account the
proposition that (contrary to previous models) emitted quarks and gluons do not
directly fragment into hadrons, but rather interact and form a photosphere and
decrease in energy before fragmenting. The resulting spectrum emits copious
amount of photons at energies around 100MeV. We find that the limit on the
average universal density of black holes is not significantly affected by the
photosphere. However we also find that gamma ray satellites such as EGRET and
GLAST are well suited to look for nearby black holes out to a distance on the
order of 0.3 parsecs, and conclude that if black holes are clustered locally as
much as luminous matter, they may be directly detectable.Comment: 10 pages, Latex, submitted to PR
Baryogenesis from Primordial Blackholes after Electroweak Phase Transition
Incorporating a realistic model for accretion of ultra-relativistic particles
by primordial blackholes (PBHs), we study the evolution of an Einstein-de
Sitter universe consisting of PBHs embedded in a thermal bath from the epoch
sec to sec. In this paper we use Barrow
et al's ansatz to model blackhole evaporation in which the modified Hawking
temperature goes to zero in the limit of the blackhole attaining a relic state
with mass . Both single mass PBH case as well as the case in which
blackhole masses are distributed in the range gm
have been considered in our analysis. Blackholes with mass larger than gm appear to survive beyond the electroweak phase transition and,
therefore, successfully manage to create baryon excess via
emissions, averting the baryon number wash-out due to sphalerons. In this
scenario, we find that the contribution to the baryon-to-entropy ratio by PBHs
of initial mass is given by , where
and are the CP-violating parameter and the initial mass
fraction of the PBHs, respectively. For larger than ,
the observed matter-antimatter asymmetry in the universe can be attributed to
the evaporation of PBHs.Comment: Latex2e file with seven figures included as postscript file
NEUTRINOS FROM PRIMORDIAL BLACK HOLES
The emission of particles from black holes created in the early Universe has
detectable astrophysical consequences. The most stringent bound on their
abundance has been obtained from the absence of a detectable diffuse flux of
100 MeV photons. Further scrutiny of these bounds is of interest as they, for
instance, rule out primordial black holes as a dark matter candidate. We here
point out that these bounds can, in principle, be improved by studying the
diffuse cosmic neutrino flux. Measurements of near-vertical atmospheric
neutrino fluxes in a region of low geomagnetic latitude can provide a
competitive bound. The most favorable energy to detect a possible diffuse flux
of primordial black hole origin is found to be a few MeV. We also show that
measurements of the diffuse flux is the most promising to improve
the existing bounds deduced from gamma-ray measurements. Neutrinos from
individual black hole explosions can be detected in the GeV-TeV energy region.
We find that the kilometer-scale detectors, recently proposed, are able to
establish competitive bounds.Comment: 19 pages plus 9 uuencoded and compressed postscript figure
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
Solar Neutrinos and the Eclipse Effect
The solar neutrino counting rate in a real time detector like
Super--Kamiokanda, SNO, or Borexino is enhanced due to neutrino oscillations in
the Moon during a partial or total solar eclipse. The enhancement is calculated
as a function of the neutrino parameters in the case of three flavor mixing.
This enhancement, if seen, can further help to determine the neutrino
parameters.Comment: 24 Pages Revtex, 8 figures as one ps file. To appear in Phys. Rev. D;
Some typos corrected and a reference adde
Searching for Very-High-Energy Gamma-Ray Bursts from Evaporating Primordial Black Holes
Temporal and energy characteristics of the very-high-energy gamma-ray bursts
from evaporating primordial black holes have been calculated by assuming that
the photospheric and chromospheric effects are negligible. The technique of
searching for such bursts on shower arrays is described. We show that the burst
time profile and the array dead time should be taken into account to interpret
experimental data. Based on data from the Andyrchy array of the Baksan Neutrino
Observatory (Institute for Nuclear Research, Russian Academy of Sciences), we
have obtained an upper limit on the number density of evaporating primordial
black holes in a local region of space with a scale size of ~10^{-3} pc.
Comparison with the results of previous experiments is made.Comment: 6 pages, 6 figure
Region of Excessive Flux of PeV Cosmic Rays in the Direction Toward Pulsars PSR J1840+5640 and LAT PSR J1836+5925
An analysis of arrival directions of extensive air showers (EAS) registered
with the EAS MSU and EAS-1000 prototype arrays has revealed a region of
excessive flux of PeV cosmic rays in the direction toward pulsars PSR
J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The
first of the pulsars was discovered almost 30 years ago and is a well-studied
old radio pulsar located at the distance of 1.7pc from the Solar system. The
second pulsar belongs to a new type of pulsars, discovered by the space
gamma-ray observatory Fermi, pulsations of which are not observed in optical
and radio wavelengths but only in the gamma-ray range of energies
(gamma-ray-only pulsars). In our opinion, the existence of the region of
excessive flux of cosmic rays registered with two different arrays provides a
strong evidence that isolated pulsars can give a noticeable contribution to the
flux of Galactic cosmic rays in the PeV energy range.Comment: 14 pages; v.2: a few remarks to match a version accepted for
Astronomy Letters added. They can be found by redefining the \NEW command in
the preamble of the LaTeX fil
Evidence for TeV gamma ray emission from Cassiopeia A
232 hours of data were accumulated from 1997 to 1999, using the HEGRA
Stereoscopic Cherenkov Telescope System to observe the supernova remnant
Cassiopeia A. TeV gamma ray emission was detected at the 5 sigma level, and a
flux of (5.8 +- 1.2(stat) +- 1.2(syst)) 10^(-9) ph m^(-2) s^(-1) above 1 TeV
was derived. The spectral distribution is consistent with a power law with a
differential spectral index of -2.5 +- 0.4(stat) +- 0.1(syst) between 1 and 10
TeV. As this is the first report of the detection of a TeV gamma ray source on
the "centi-Crab" scale, we present the analysis in some detail. Implications
for the acceleration of cosmic rays depend on the details of the source
modeling. We discuss some important aspects in this paper.Comment: 9 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Observation of the Shadowing of Cosmic Rays by the Moon using a Deep Underground Detector
Using data collected by the MACRO experiment during the years 1989-1996, we
show evidence for the shadow of the moon in the underground cosmic ray flux
with a significance of 3.6 sigma. This detection of the shadowing effect is the
first by an underground detector. A maximum-likelihood analysis is used to
determine that the angular resolution of the apparatus is 0.9+/-0.3 degrees.
These results demonstrate MACRO's capabilities as a muon telescope by
confirming its absolute pointing ability and quantifying its angular
resolution.Comment: 14 pages, 8 figures Submitted to Phys. Rev.