14 research outputs found
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
Lorentz breaking Effective Field Theory and observational tests
Analogue models of gravity have provided an experimentally realizable test
field for our ideas on quantum field theory in curved spacetimes but they have
also inspired the investigation of possible departures from exact Lorentz
invariance at microscopic scales. In this role they have joined, and sometime
anticipated, several quantum gravity models characterized by Lorentz breaking
phenomenology. A crucial difference between these speculations and other ones
associated to quantum gravity scenarios, is the possibility to carry out
observational and experimental tests which have nowadays led to a broad range
of constraints on departures from Lorentz invariance. We shall review here the
effective field theory approach to Lorentz breaking in the matter sector,
present the constraints provided by the available observations and finally
discuss the implications of the persisting uncertainty on the composition of
the ultra high energy cosmic rays for the constraints on the higher order,
analogue gravity inspired, Lorentz violations.Comment: 47 pages, 4 figures. Lecture Notes for the IX SIGRAV School on
"Analogue Gravity", Como (Italy), May 2011. V.3. Typo corrected, references
adde
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