259 research outputs found
Ultra-High Energy Cosmic Rays and Diffuse Photon Spectrum
It is argued that if extragalactic magnetic fields are smaller than
2x10^{-12} G the flux of ultra-high energy photons of (a few)x10^{-1} eV
cm^{-2}s^{-1}sr^{-1} predicted in the top-down models of UHE CR implies similar
flux of the diffuse photons in the energy range 10^{15}-10^{17} eV, which is
close to the existing experimental limit.Comment: Talk given at XI Rencontres de Blois. 3 pages, no figure
Correlations and Charge Composition of UHECR without Knowledge of Galactic Magnetic Field
We develop a formalism which allows to study correlations of charged UHECR
with potential sources without using any Galactic Magnetic Field (GMF) model.
The method is free of subjective chose of parameters on which the significance
of correlations depends strongly. We show that correlations of the AGASA
dataset with BL Lacs (found previously after reconstruction of particle
trajectories in a specific GMF) are present intrinsically and can be detected
without reference to a particular model of magnetic field.Comment: To be published in the Proceedings of the 28th International Cosmic
Ray Conferenc
Sources of sub-GZK cosmic rays
We analyze the existing evidence that BL Lacertae objects (BL Lacs) are
sources of the highest-energy cosmic rays. We argue that three independent
signatures observed in the real data -- (1) improvement of correlations with
corrections of trajectories for the Galactic magnetic field; (2) connection
between gamma-ray and UHECR emissions; (3) non-uniform distribution of
correlating rays over the sky -- are consistent with the hypothesis that a
substantial fraction of cosmic rays in the energy range 40-60 EeV are protons
accelerated in BL Lacs.Comment: Talk at the International Workshop on Extremely High Energy Cosmic
Rays, November 5-6, 2002, RIKEN, Japa
Cuts and penalties: comment on "The clustering of ultra-high energy cosmic rays and their sources"
In a series of papers we have found statistically significant correlations
between arrival directions of ultra-high energy cosmic rays and BL Lacertae
objects. Recently, our calculations were partly repeated by Evans, Ferrer and
Sarkar with different conclusions. We demonstrate that the criticism of Evans,
Ferrer and Sarkar is incorrect. We also present the details of our method.Comment: Replaced with version accepted for publication in Phys. Rev.
Full sky harmonic analysis hints at large UHECR deflections
The full-sky multipole coefficients of the ultra-high energy cosmic ray
(UHECR) flux have been measured for the first time by the Pierre Auger and
Telescope Array collaborations using a joint data set with E > 10 EeV. We
calculate these harmonic coefficients in the model where UHECR are protons and
sources trace the local matter distribution, and compare our results with
observations. We find that the expected power for low multipoles (dipole and
quadrupole, in particular) is sytematically higher than in the data: the
observed flux is too isotropic. We then investigate to which degree our
predictions are influenced by UHECR deflections in the regular Galactic
magnetic field (GMF). It turns out that the UHECR power spectrum coefficients
are quite insensitive to the effects of the GMF, so it is unlikely
that the discordance can be reconciled by tuning the GMF model. On the
contrary, a sizeable fraction of uniformly distributed flux (representing for
instance an admixture of heavy nuclei with considerably larger deflections) can
bring simulations and observations to an accord.Comment: 8 pages, 4 figures and one table, JETPL style -- v2 as published in
JETP
Cosmological attractors in massive gravity
We study Lorentz-violating models of massive gravity which preserve rotations
and are invariant under time-dependent shifts of the spatial coordinates. In
the linear approximation the Newtonian potential in these models has an extra
``confining'' term proportional to the distance from the source. We argue that
during cosmological expansion the Universe may be driven to an attractor point
with larger symmetry which includes particular simultaneous dilatations of time
and space coordinates. The confining term in the potential vanishes as one
approaches the attractor. In the vicinity of the attractor the extra
contribution is present in the Friedmann equation which, in a certain range of
parameters, gives rise to the cosmic acceleration.Comment: 26 pages, 1 figur
Detection prospects of the Telescope Array hotspot by space observatories
In the present-day cosmic ray data, the strongest indication of anisotropy of
the ultrahigh energy cosmic rays is the 20-degree hotspot observed by the
Telescope Array with the statistical significance of 3.4\sigma. In this work,
we study the possibility of detecting such a spot by space-based all-sky
observatories. We show that if the detected luminosity of the hotspot is
attributed to a physical effect and not a statistical fluctuation, the KLYPVE
and JEM-EUSO experiments would need to collect ~300 events with E>57 EeV in
order to detect the hotspot at the 5\sigma\ confidence level with the 68%
probability. We also study the dependence of the detection prospects on the
hotspot luminosity.Comment: 4 pages; v2: minor style changes to match the published versio
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
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