2,905 research outputs found
Effects of the galactic magnetic field upon large scale anisotropies of extragalactic Cosmic Rays
The large scale pattern in the arrival directions of extragalactic cosmic
rays that reach the Earth is different from that of the flux arriving to the
halo of the Galaxy as a result of the propagation through the galactic magnetic
field. Two different effects are relevant in this process: deflections of
trajectories and (de)acceleration by the electric field component due to the
galactic rotation. The deflection of the cosmic ray trajectories makes the flux
intensity arriving to the halo from some direction to appear reaching the Earth
from another direction. This applies to any intrinsic anisotropy in the
extragalactic distribution or, even in the absence of intrinsic anisotropies,
to the dipolar Compton-Getting anisotropy induced when the observer is moving
with respect to the cosmic rays rest frame. For an observer moving with the
solar system, cosmic rays traveling through far away regions of the Galaxy also
experience an electric force coming from the relative motion (due to the
rotation of the Galaxy) of the local system in which the field can be
considered as being purely magnetic. This produces small changes in the
particles momentum that can originate large scale anisotropies even for an
isotropic extragalactic flux.Comment: 11 pages, 4 figure
Scalar Non-Luminous Matter in Galaxies
As a candidate for dark matter in galaxies, we study an SU(3) triplet of
complex scalar fields which are non-minimally coupled to gravity. In the
spherically symmetric static spacetime where the flat rotational velocity
curves of stars in galaxies can be explained, we find simple solutions of
scalar fields with SU(3) global symmetry broken to U(1) X U(1), in an
exponential scalar potential, which will be useful in a quintessence model of
the late-time acceleration of the Universe.Comment: 6 pages, no figure, LaTex. Submitted to IJMP
Ultrahigh Energy Nuclei in the Galactic Magnetic Field
Observations are consistent with a significant fraction of heavy nuclei in
the cosmic ray flux above a few times 10^19 eV. Such nuclei can be deflected
considerably in the Galactic magnetic field, with important implications for
the search of their sources. We perform detailed simulations of heavy nuclei
propagation within recent Galactic magnetic field models. While such models are
not yet sufficiently constrained to predict deflection maps in detail, we find
general features of the distribution of (de-) magnified flux from sources.
Since in most theoretical models sources of heavy nuclei are located in the
local large scale structure of galaxies, we show examples of images of several
nearby galaxy clusters and of the supergalactic plane. Such general features
may be useful to develop efficient methods for source reconstruction from
observed ultrahigh energy cosmic ray arrival directions.Comment: 17 pages, 11 figures. Published in JCA
Search for single sources of ultra high energy cosmic rays on the sky
In this paper, we suggest a new way to identify single bright sources of
Ultra High Energy Cosmic Rays (UHECR) on the sky, on top of background. We look
for doublets of events at the highest energies, E > 6 x 10^19 eV, and identify
low energy tails, which are deflected by the Galactic Magnetic Field (GMF). For
the sources which are detected, we can recover their angular positions on the
sky within one degree from the real ones in 68% of cases. The reconstruction of
the deflection power of the regular GMF is strongly affected by the value of
the turbulent GMF. For typical values of 4 microG near the Earth, one can
reconstruct the deflection power with 25% precision in 68% of cases.Comment: 20 pages, 10 figures. Corresponds to the version published in JCA
Global monopoles and scalar fields as the electrogravity dual of Schwarzschild spacetime
We prove that both global monopole and minimally coupled static zero mass
scalar field are electrogravity dual of the Schwarzschild solution or flat
space and they share the same equation of state, . This
property was however known for the global monopole spacetime while it is for
the first time being established for the scalar field. In particular, it turns
out that the Xanthopoulos - Zannias scalar field solution is dual to flat
space.Comment: 5 pages, RevTe
Recent results from the Pierre Auger Observatory
The main results from the Auger Observatory are described. A steepening of
the spectrum is observed at the highest energies, supporting the expectation
that above eV the cosmic ray energies are significantly
degraded by interactions with the CMB photons (the GZK effect). This is further
supported by the correlations observed above eV with the
distribution of nearby active galaxies, which also show the potential of Auger
to start the era of charged particle astronomy. The lack of observation of
photons or neutrinos strongly disfavors top-down models, and these searches may
approach in the long term the sensitivity required to test the fluxes expected
from the secondaries of the very same GZK process. Bounds on the anisotropies
at EeV energies contradict hints from previous experiments that suggested a
large excess from regions near the Galactic centre or the presence of a dipolar
type modulation of the cosmic ray flux.Comment: 6 p., 8 figs., proceedings of the XXIII International Conference on
Neutrino Physics and Astrophysics (Neutrino 08
Lensing of ultra-high energy cosmic rays in turbulent magnetic fields
We consider the propagation of ultra high energy cosmic rays through
turbulent magnetic fields and study the transition between the regimes of
single and multiple images of point-like sources. The transition occurs at
energies around , where is the distance traversed by the
CR's with electric charge in the turbulent magnetic field of root mean
square strength and coherence length . We find that above only sources located in a fraction of a few % of the sky can reach large
amplifications of its principal image or start developing multiple images. New
images appear in pairs with huge magnifications, and they remain amplified over
a significant range of energies. At decreasing energies the fraction of the sky
in which sources can develop multiple images increases, reaching about 50% for
. The magnification peaks become however increasingly narrower and for
their integrated effect becomes less noticeable. If a uniform
magnetic field component is also present it would further narrow down the
peaks, shrinking the energy range in which they can be relevant. Below some kind of scintillation regime is reached, where many demagnified
images of a source are present but with overall total magnification of order
unity. We also search for lensing signatures in the AGASA data studying
two-dimensional correlations in angle and energy and find some interesting
hints.Comment: 30 pages, 16 figures, final version with minor change
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