17 research outputs found
Probing Lorentz Invariance at EeV Energy
Pierre Auger experiment has detected at least a couple of ray events above
energy 60 EeV from the direction of the radio-galaxy Centaurus A. Assuming
those events are from Centaurus A, we have calculated the number of neutral
cosmic ray events from this source for small values of the degree of violation
in Lorentz invariance. Our results show that a comparison of our calculated
numbers of events with the observed number of events at EeV energy from the
direction of the source can probe extremely low value of the degree of this
violation.Comment: 8 pages,4 figure
UHECR as Decay Products of Heavy Relics? The Lifetime Problem
The essential features underlying the top-down scenarii for UHECR are
discussed, namely, the stability (or lifetime) imposed to the heavy objects
(particles) whatever they be: topological and non-topological solitons,
X-particles, cosmic defects, microscopic black-holes, fundamental strings. We
provide an unified formula for the quantum decay rate of all these objects as
well as the particle decays in the standard model. The key point in the
top-down scenarii is the necessity to adjust the lifetime of the heavy object
to the age of the universe. This ad-hoc requirement needs a very high
dimensional operator to govern its decay and/or an extremely small coupling
constant. The natural lifetimes of such heavy objects are, however, microscopic
times associated to the GUT energy scale (sim 10^{-28} sec. or shorter). It is
at this energy scale (by the end of inflation) where they could have been
abundantly formed in the early universe and it seems natural that they decayed
shortly after being formed.Comment: 11 pages, LaTex, no figures, updated versio
Ultrahigh energy cosmic rays from collisional annihilation revisited
We re-examine collisional annihilation of superheavy dark matter particles in
dark matter density spikes in the galactic halo as a possible source of
ultrahigh energy cosmic rays. We estimate the possible flux in a way that does
not depend on detailed assumptions about the density profiles of dark matter
clumps. The result confirms that collisional annihilation is compatible with
annihilation cross sections below the unitarity bounds for superheavy dark
matter if the particles can form dense cores in dark matter substructure, and
it provides estimates for core sizes and densities. The ensuing clumpy source
distribution in the galactic halo will be tested within a few years of
operation of the Pierre Auger observatory.Comment: 9 pages, new section included, introduction shortened, to appear in
Can. J. Phy
Loop Quantum Gravity and Ultra High Energy Cosmic Rays
There are two main sets of data for the observed spectrum of ultra high
energy cosmic rays (those cosmic rays with energies greater than eV), the High Resolution Fly's Eye (HiRes) collaboration group
observations, which seem to be consistent with the predicted theoretical
spectrum (and therefore with the theoretical limit known as the
Greisen-Zatsepin-Kuzmin cutoff), and the observations from the Akeno Giant Air
Shower Array (AGASA) collaboration group, which reveal an abundant flux of
incoming particles with energies above eV violating the
Greisen-Zatsepin-Kuzmin cutoff. As an explanation of this anomaly it has been
suggested that quantum-gravitational effects may be playing a decisive role in
the propagation of ultra high energy cosmic rays. In this article we take the
loop quantum gravity approach. We shall provide some techniques to establish
and analyze new constraints on the loop quantum gravity parameters arising from
both sets of data, HiRes and AGASA . We shall also study their effects on the
predicted spectrum for ultra high energy cosmic rays. As a result we will state
the possibility of reconciling the AGASA observations.Comment: 18 pages, latex, 4 figure
Plastic optical fibre sensors for structural health monitoring: A review of recent progress
10.1155/2009/312053Journal of Sensors2009