567 research outputs found
SimProp: a Simulation Code for Ultra High Energy Cosmic Ray Propagation
A new Monte Carlo simulation code for the propagation of Ultra High Energy
Cosmic Rays is presented. The results of this simulation scheme are tested by
comparison with results of another Monte Carlo computation as well as with the
results obtained by directly solving the kinetic equation for the propagation
of Ultra High Energy Cosmic Rays. A short comparison with the latest flux
published by the Pierre Auger collaboration is also presented.Comment: 19 pages, 12 eps figures, version accepted for publication in JCA
Lorentz Invariance and the semiclassical approximation of loop quantum gravity
It is shown that the field equations derived from an effective interaction
hamiltonian for Maxwell and gravitational fields in the semiclassical
approximation of loop quantum gravity using rotational invariant states (such
as weave states) are Lorentz invariant. To derive this result, which is in
agreement with the observational evidence, we use the geometrical properties of
the electromagnetic field.Comment: 6 page
Astrophysical Neutrino Event Rates and Sensitivity for Neutrino Telescopes
Spectacular processes in astrophysical sites produce high-energy cosmic rays
which are further accelerated by Fermi-shocks into a power-law spectrum. These,
in passing through radiation fields and matter, produce neutrinos. Neutrino
telescopes are designed with large detection volumes to observe such
astrophysical sources. A large volume is necessary because the fluxes and
cross-sections are small. We estimate various telescopes' sensitivities and
expected event rates from astrophysical sources of high-energy neutrinos. We
find that an ideal detector of km^2 incident area can be sensitive to a flux of
neutrinos integrated over energy from 10^5 and 10^{7} GeV as low as 1.3 *
10^(-8) * E^(-2) (GeV/cm^2 s sr) which is three times smaller than the
Waxman-Bachall conservative upper limit on potential neutrino flux. A real
detector will have degraded performance. Detection from known point sources is
possible but unlikely unless there is prior knowledge of the source location
and neutrino arrival time.Comment: Section added +modification
Prospect of determining the Dirac/Majorana state of neutrino by Multi-OWL experiment
We consider the non-radiative two body decay of a neutrino to a daughter
neutrino with degraded energy and a very light particle (Majoron). Ultrahigh
energy neutrinos from an astrophysical source like a Gamma Ray Burst undergoing
this decay process are found to produce different number of events in the
detector depending on whether they are Majorana or Dirac particles. The next
generation large scale experiments like Multi-OWL is expected to provide us an
accurate determination of the flux of neutrinos from astrophysical sources and
this may enable us to distinguish between the Dirac and Majorana nature of
neutrino.Comment: 18 pages latex, no figure. Journal of Phys. G in pres
Astrophysical Bounds on Planck Suppressed Lorentz Violation
This article reviews many of the observational constraints on Lorentz
symmetry violation (LV). We first describe the GZK cutoff and other phenomena
that are sensitive to LV. After a brief historical sketch of research on LV, we
discuss the effective field theory description of LV and related questions of
principle, technical results, and observational constraints. We focus on
constraints from high energy astrophysics on mass dimension five operators that
contribute to LV electron and photon dispersion relations at order E/M_Planck.
We also briefly discuss constraints on renormalizable operators, and review the
current and future contraints on LV at order (E/M_Planck)^2.Comment: 30 pages, submitted to Lecture Notes in Physics, Quantum Gravity
Phenomenology, eds. G.Amelino-Camelia, J. Kowalski-Glikman (Springer-Verlag
High Energy Neutrinos from Quasars
We review and clarify the assumptions of our basic model for neutrino
production in the cores of quasars, as well as those modifications to the model
subsequently made by other workers. We also present a revised estimate of the
neutrino background flux and spectrum obtained using more recent empirical
studies of quasars and their evolution. We compare our results with other
thoeretical calculations and experimental upper limits on the AGN neutrino
background flux. We also estimate possible neutrino fluxes from the jets of
blazars detected recently by the EGRET experiment on the Compton Gamma Ray
Observatory. We discuss the theoretical implications of these estimates.Comment: 14 pg., ps file (includes figures), To be published in Space Science
Review
Cosmic Physics: The High Energy Frontier
Cosmic rays have been observed up to energies times larger than those
of the best particle accelerators. Studies of astrophysical particles (hadrons,
neutrinos and photons) at their highest observed energies have implications for
fundamental physics as well as astrophysics. Thus, the cosmic high energy
frontier is the nexus to new particle physics. This overview discusses recent
advances being made in the physics and astrophysics of cosmic rays and cosmic
gamma-rays at the highest observed energies as well as the related physics and
astrophysics of very high energy cosmic neutrinos. These topics touch on
questions of grand unification, violation of Lorentz invariance, as well as
Planck scale physics and quantum gravity.Comment: Topical Review Paper to be published in the Journal of Physics G, 50
page
Ribbons on the CBR Sky: A Powerful Test of a Baryon Symmetric Universe
If the Universe consists of domains of matter and antimatter, annihilations
at domain interfaces leave a distinctive imprint on the Cosmic Background
Radiation (CBR) sky. The signature is anisotropies in the form of long, thin
ribbons of width , separated by angle where L is the characteristic domain size, and
y-distortion parameter . Such a pattern could potentially be
detected by the high-resolution CBR anisotropy experiments planned for the next
decade, and such experiments may finally settle the question of whether or not
our Hubble volume is baryon symmetric.Comment: LaTeX, 10 pages, 4 figures in epsf. Revised version corrects a couple
of relevant mistake
Yet Another Model of Gamma-Ray Bursts
Sari and Piran have demonstrated that the time structure of gamma-ray bursts
must reflect the time structure of their energy release. A model which
satisfies this condition uses the electrodynamic emission of energy by the
magnetized rotating ring of dense matter left by neutron star coalescence; GRB
are essentially fast, high field, differentially rotating pulsars. The energy
densities are large enough that the power appears as an outflowing equilibrium
pair plasma, which produces the burst by baryon entrainment and subsequent
internal shocks. I estimate the magnetic field and characteristic time scale
for its rearrangement, which determines the observed time structure of the
burst. There may be quasi-periodic oscillations at the rotational frequencies,
which are predicted to range up to 5770 Hz (in a local frame). This model is
one of a general class of electrodynamic accretion models which includes the
Blandford and Lovelace model of AGN, and which can also be applied to black
hole X-ray sources of stellar mass. The apparent efficiency of nonthermal
particle acceleration is predicted to be 10--50%, but higher values are
possible if the underlying accretion flow is super-Eddington. Applications to
high energy gamma-ray observations of AGN are briefly discussed.Comment: 21pp, latex, uses aaspp4.st
Neutrino production through hadronic cascades in AGN accretion disks
We consider the production of neutrinos in active galactic nuclei (AGN)
through hadronic cascades. The initial, high energy nucleons are accelerated in
a source above the accretion disk around the central black hole. From the
source, the particles diffuse back to the disk and initiate hadronic cascades.
The observable output from the cascade are electromagnetic radiation and
neutrinos. We use the observed diffuse background X-ray luminosity, which
presumably results {}from this process, to predict the diffuse neutrino flux
close to existing limits from the Frejus experiment. The resulting neutrino
spectrum is down to the \GeV region. We discuss modifications of
this scenario which reduce the predicted neutrino flux.Comment: 12 Pages, LaTeX, TK 92 0
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