325 research outputs found
Recent results from the Pierre Auger Observatory
The results obtained after the first decade of operation of the Pierre Auger
Observatory are reviewed.Comment: Proceedings X SILAFAE Medellin-201
Results from the Pierre Auger Observatory
I describe some of the results on ultrahigh-energy cosmic rays that have been
obtained with the Pierre Auger Observatory. These include measurements of the
spectrum, composition and anisotropies. Possible astrophysical scenarios that
account for these results are discussed.Comment: Proceedings of the 7th Roma International Conference on Astroparticle
Physic
Electron neutrino opacity in magnetised media
We study the effects of strong magnetic fields (~G) in the cross
section for scattering in the presence of a degenerate
electron background. This can be relevant for the propagation in the
proto-neutron star stage after supernovae collapse. We find that for field
strengths ~G MeV the opacity is sizeably
affected by the magnetic field and can lead to a shift in the location of the
electron neutrino sphere towards lower densities.
We discuss the implications that this may have for scenarios proposed to
explain the observed pulsar velocities
Microlensing searches of dark matter
The evolution of the observational results of microlensing towards the
LMC and some of the suggested interpretations to account for them are
discussed. It is emphasized that the results at present are indicative of a
lensing population of white dwarfs, possibly in the spheroid (not dark halo) of
the Galaxy, together with the more standard backgrounds of stellar populations
in the Magellanic Clouds and in the
Galaxy. This is also hinted by dynamical estimates of the spheroid mass and
by recent direct searches of old white dwarfs.Comment: 9 pp., Lecture given at Silafae III Conference (april 2000
E sub 6 leptoquarks and the solar neutrino problem
The possibility that non-conventional neutrino oscillations take place in the superstring inspired E sub 6 models is considered. In this context, the influence of leptoquark mediated interactions of the neutrinos with nucleons in the resonant flavor conversion is discussed. It is shown that this effect can be significant for v sub e - v sub tau oscillations if these neutrinos have masses required in the ordinary Mikheyev-Smirnov-Wolfenstein (MSW) effect, and may lead to a solution of the solar neutrino problem even in the absence of vacuum mixings. On the other hand, this model cannot lead to a resonant behavior in the sun if the neutrinos are massless
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
Neutrino Masses
This is a review for Reports of Progress in Physics. After an introduction we
start by explaining the different neutrino masses corresponding to different
types of neutrinos, Dirac or Majorana, in section 2. In section 3 we discuss
the main elementary particle models for neutrino masses and their distinctive
phenomenological consequences. In section 4 we describe the status of direct
mass searches and Majorana mass searches in neutrinoless double beta decays. In
section 5 we go over the many cosmological implications of, and constraints on,
neutrino properties, mainly masses and lifetimes. Sections 6, 7 and 8 review
neutrino oscillations, the solar neutrino problem and the atmospheric neutrino
problem, their implications and the current and future experiments. In
particular, we explain oscillations in vacuum in section 6 and oscillations in
matter in section 7. Section 9 summarizes the main bounds imposed by stars,
mainly SN1987A. A few concluding remarks follow.Comment: 85 pp.,Tex file requires ioppreprint.sty and verbatim.tex, 12 figures
sent separately in a uu-compressed fil
On the propagation of the highest energy cosmic ray nuclei
We study the propagation of ultra-high energy cosmic ray nuclei through the
background of cosmic microwave and intergalactic infrared photons, using recent
re-estimates for the density of the last ones. We perform a detailed Monte
Carlo simulation to follow the disintegration histories of nuclei starting as
Fe and reaching the Earth from extragalactic sources. We obtain the maximum
energies of the arriving nuclear fragments as well as the mass composition as a
function of the distance traveled. Cosmic rays with energies in excess of
eV cannot originate from Fe nuclei produced in sources beyond
10 Mpc.Comment: 8 page
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