14,219 research outputs found
Ensemble fluctuations of the cosmic ray energy spectrum and the intergalactic magnetic field
The origin of the most energetic cosmic ray particles is one of the most
important open problems in astrophysics. Despite a big experimental effort done
in the past years, the sources of these very energetic particles remain
unidentified. Therefore, their distribution on the Universe and even their
space density are still unknown. It has been shown that different spatial
configurations of the sources lead to different energy spectra and composition
profiles (in the case of sources injecting heavy nuclei) at Earth. These
ensemble fluctuations are more important at the highest energies because only
nearby sources, which are necessarily few, can contribute to the flux observed
at Earth. This is due to the interaction of the cosmic rays with the low energy
photons of the radiation field, present in the intergalactic medium, during
propagation. It is believed that the intergalactic medium is permeated by a
turbulent magnetic field. Although at present it is still unknown, there are
several constraints for its intensity and coherence length obtained from
different observational techniques. Charged cosmic rays are affected by the
intergalactic magnetic field because of the bending of their trajectories
during propagation through the intergalactic medium. In this work, the
influence of the intergalactic magnetic field on the ensemble fluctuations is
studied. Sources injecting only protons and only iron nuclei are considered.
The ensemble fluctuations are studied for different values of the density of
sources compatible with the constraints recently obtained from cosmic ray data.
Also, the possible detection of the ensemble fluctuations in the context of the
future JEM-EUSO mission is discussed.Comment: Accepted for publication in Physical Review
On the possibility of neutrino flavor identification at the highest energies
High energy astrophysical neutrinos carry relevant information about the
origin and propagation of cosmic rays. They can be created as a by-product of
the interactions of cosmic rays in the sources and during propagation of these
high energy particles through the intergalactic medium. The determination of
flavor composition in this high energy flux is important because it presents a
unique chance to probe our understanding of neutrino flavor oscillations at
gamma factors >10^21. In this work we develop a new statistical technique to
study the flavor composition of the incident neutrino flux, which is based on
the multipeak structure of the longitudinal profiles of very deep electron and
tau neutrino horizontal air showers. Although these longitudinal profiles can
be observed by means of fluorescence telescopes placed over the Earth's
surface, orbital detectors are more suitable for neutrino observations owing to
their much larger aperture. Therefore, we focus on the high energy region of
the neutrino spectrum relevant for observations with orbital detectors like the
planned JEM-EUSO telescope.Comment: Accepted for publication in Physical Review
From sensorimotor dependencies to perceptual practices: making enactivism social
Proponents of enactivism should be interested in exploring what notion of action best captures the type of action-perception link that the view proposes, such that it covers all the aspects in which our doings constitute and are constituted by our perceiving. This article proposes and defends the thesis that the notion of sensorimotor dependencies is insufficient to account for the reality of human perception, and that the central enactive notion should be that of perceptual practices. Sensorimotor enactivism is insufficient because it has no traction on socially dependent perceptions, which are essential to the role and significance of perception in our lives. Since the social dimension is a central desideratum in a theory of human perception, enactivism needs a notion that accounts for such an aspect. This article sketches the main features of the Wittgenstein-inspired notion of perceptual practices as the central notion to understand perception. Perception, I claim, is properly understood as woven into a type of social practices that includes food, dance, dress, music, etc. More specifically, perceptual practices are the enactment of culturally structured, normatively rich techniques of commerce of meaningful multi- and inter-modal perceptible material. I argue that perceptual practices explain three central features of socially dependent perception: attentional focus, aspects’ saliency, and modal-specific harmony-like relations
Improving photon-hadron discrimination based on cosmic ray surface detector data
The search for photons at EeV energies and beyond has considerable
astrophysical interest and will remain one of the key challenges for ultra-high
energy cosmic ray (UHECR) observatories in the near future. Several upper
limits to the photon flux have been established since no photon has been
unambiguously observed up to now. An improvement in the reconstruction
efficiency of the photon showers and/or better discrimination tools are needed
to improve these limits apart from an increase in statistics. Following this
direction, we analyze in this work the ability of the surface parameter Sb,
originally proposed for hadron discrimination, for photon search.
Semi-analytical and numerical studies are performed in order to optimize Sb
for the discrimination of photons from a proton background in the energy range
from 10^18.5 to 10^19.6 eV. Although not shown explicitly, the same analysis
has been performed for Fe nuclei and the corresponding results are discussed
when appropriate. The effects of different array geometries and the
underestimation of the muon component in the shower simulations are analyzed,
as well as the Sb dependence on primary energy and zenith angle.Comment: 9 pages, 19 Figures. Accepted in Astroparticle Physics on May 31th,
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