268 research outputs found
Magnetic diffusion effects on the Ultra-High Energy Cosmic Ray spectrum and composition
We discuss the effects of diffusion of high energy cosmic rays in turbulent
extra-galactic magnetic fields. We find an approximate expression for the low
energy suppression of the spectrum of the different mass components (with
charge ) in the case in which this suppression happens at energies below
EeV, so that energy losses are dominated by the adiabatic ones.
The low energy suppression appears when cosmic rays from the closest sources
take a time comparable to the age of the Universe to reach the Earth. This
occurs for energies in terms of the magnetic field RMS strength , its
coherence length and the typical separation between sources .
We apply this to scenarios in which the sources produce a mixed composition
and have a relatively low maximum rigidity (-- EeV),
finding that diffusion has a significant effect on the resulting spectrum, the
average mass and on its spread, in particular reducing this last one. For
reasonable values of and these effects can help to reproduce the
composition trends observed by the Auger Collaboration for source spectra
compatible with Fermi acceleration
Axino-induced baryogenesis
We consider the possibility that the baryon asymmetry is generated at low energies as a consequence of the axino decay. We analyze models in which the axino, the superpartner of the axion, is heavy and decays into gluinos at temperatures T approx. = 1 GeV. If CP and B violating couplings for the quark superfields are included, the subsequent decay of these out of equilibrium gluinos can act as seeds for baryogenesis. The required amount of CP violation is well consistent with the bounds on the electric dipole moment of the neutron and the mechanism works even for low reheating temperatures after inflation (T sub RH greater or approx. = 10 exp 4 GeV)
Angular distribution of cosmic rays from an individual source in a turbulent magnetic field
We obtain the angular distribution of the cosmic rays reaching an observer
from an individual source and after propagation through a turbulent magnetic
field, for different ratios between the source distance and the diffusion
length. We study both the high-energy quasi-rectilinear regime as well as the
transition towards the diffusive regime at lower energies where the deflections
become large. We consider the impact of energy losses, showing that they tend
to enhance the anisotropy of the source at a given energy. We also discuss
lensing effects, in particular those that could result from the regular
galactic magnetic field component, and show that the effect of the turbulent
extragalactic magnetic fields can smooth out the divergent magnification peaks
that would result for point-like sources in the limit of no turbulent
deflections.Comment: matches published versio
Anisotropies of ultra-high energy cosmic ray nuclei diffusing from extragalactic sources
We obtain the dipolar anisotropies in the arrival directions of ultra-high
energy cosmic ray nuclei diffusing from nearby extragalactic sources. We
consider mixed-composition scenarios in which different cosmic ray nuclei are
accelerated up to the same maximum rigidity, so that , with
the atomic number and the maximum proton energy. We adopt
EeV so as to account for an increasingly heavier
composition above the ankle. We obtain the anisotropies through Monte Carlo
simulations that implement the cosmic ray diffusion in extragalactic turbulent
fields as well as the effects of photo-disintegrations and other energy losses.
Dipolar anisotropies at the level of 5 to 10\% at energies ~EeV are
predicted for plausible values of the source density and magnetic fields
The toes of the ultra high energy cosmic ray spectrum
We study the effects of the galactic magnetic field on the ultra high energy
cosmic ray propagation. We show that the deflections of the cosmic ray
trajectories can have many important implications such as (de)magnification of
the cosmic ray fluxes by lensing effects (which can modify the spectrum of
individual sources), the formation of multiple images of a source or the
existence of regions of the sky to which the Earth is almost blind. The
appearance of image pairs is related to the existence of critical curves in the
magnification maps, which divide regions in the sky where the images have
opposite parities. The results are pictorially illustrated as the stretching
and folding of a `sheet' describing the sky seen on Earth. Making use of the
most energetic AGASA events we emphasize the need to know the cosmic ray
composition and the structure of the magnetic field when attempting to do
detailed cosmic ray astronomy.Comment: 22 pages, uses JHEP.cl
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