351 research outputs found
Simulation Studies of Delta-ray Backgrounds in a Compton-Scatter Transition Radiation Detector
In order to evaluate the response to cosmic-ray nuclei of a Compton-Scatter
Transition Radiation Detector in the proposed ACCESS space-based mission, a
hybrid Monte Carlo simulation using GEANT3 and an external transition radiation
(TR) generator routine was constructed. This simulation was employed to study
the effects of delta-ray production induced by high-energy nuclei and to
maximize the ratio of TR to delta-ray background. The results demonstrate the
ability of a Compton-Scatter Transition Radiation Detector to measure nuclei
from boron to iron up to Lorentz factors ~ 10^5 taking into account the steeply
falling power-law cosmic ray spectra.Comment: Presented at TRDs for the 3rd millennium: Third Workshop on advanced
Transition Radiation Detectors for accelerator and space applications,
Ostuni, Italy, September 2005, 4 pages, 2 figure
On the Direct Detection of Dark Matter Annihilation
We investigate the direct detection phenomenology of a class of dark matter
(DM) models in which DM does not directly interact with nuclei, {but rather}
the products of its annihilation do. When these annihilation products are very
light compared to the DM mass, the scattering in direct detection experiments
is controlled by relativistic kinematics. This results in a distinctive recoil
spectrum, a non-standard and or even absent annual modulation, and the ability
to probe DM masses as low as a 10 MeV. We use current LUX data to show
that experimental sensitivity to thermal relic annihilation cross sections has
already been reached in a class of models. Moreover, the compatibility of dark
matter direct detection experiments can be compared directly in
space without making assumptions about DM astrophysics, mass, or scattering
form factors. Lastly, when DM has direct couplings to nuclei, the limit from
annihilation to relativistic particles in the Sun can be stronger than that of
conventional non-relativistic direct detection by more than three orders of
magnitude for masses in a 2-7 GeV window.Comment: 4 pages, 3 figures, PRL versio
Halo Independent Direct Detection of Momentum-Dependent Dark Matter
We show that the momentum dependence of dark matter interactions with nuclei
can be probed in direct detection experiments without knowledge of the dark
matter velocity distribution. This is one of the few properties of DM
microphysics that can be determined with direct detection alone, given a signal
of dark matter in multiple direct detection experiments with different targets.
Long-range interactions arising from the exchange of a light mediator are one
example of momentum-dependent DM. For data produced from the exchange of a
massless mediator we find for example that the mediator mass can be constrained
to be MeV for DM in the 20-1000 GeV range in a halo-independent
manner.Comment: 15 pages, 4 figures; updated to match published versio
Neutrino scattering and flavor transformation in supernovae
We argue that the small fraction of neutrinos that undergo direction-changing
scattering outside of the neutrinosphere could have significant influence on
neutrino flavor transformation in core-collapse supernova environments. We show
that the standard treatment for collective neutrino flavor transformation is
adequate at late times, but could be inadequate in the crucial shock
revival/explosion epoch of core-collapse supernovae, where the potentials that
govern neutrino flavor evolution are affected by the scattered neutrinos.
Taking account of this effect, and the way it couples to entropy and
composition, will require a new paradigm in supernova modeling.Comment: 5 pages, 3 figure
Halo Modification of a Supernova Neutronization Neutrino Burst
We give the first self-consistent calculation of the effect of the scattered
neutrino halo on flavor evolution in supernovae. Our example case is an O-Ne-Mg
core collapse supernova neutronization neutrino burst. We find that the
addition of the halo neutrinos produces qualitative and quantitative changes in
the final flavor states of neutrinos. We also find that the halo neutrinos
produce a novel distortion of the neutrino flavor swap. Our results provide
strong motivation for tackling the full multidimensional and
composition-dependent aspects of this problem in the future.Comment: 14 pages, 13 figures, 1 tabl
La paradoja balear: ¿por qué las islas fueron colonizadas tan tarde?
Research on Mediterranean islands has pushed the evidence for initial human presence backwardsin time, with 75% occupied by the 4th millennium BC. Yet data from the Balearics suggest that themost likely window for human arrival there is in the last half, and perhaps the final third, of the 3rdmillennium BC. We refer to this disparity as the “Balearic paradox”—why were these large islandscolonized so late? We contextualize the Balearic data, suggesting that “push” and “pull” factors wouldhave affected the willingness of mainland-based agropastoralists to undertake colonization endeavors.We consider the need for improved understanding of socioeconomic, environmental, and climaticfactors in likely colonist source areas.La investigación sobre las islas mediterráneas ha hecho retroceder en el tiempo las primeras evidenciasde ocupación humana, con un 75% de ellas ocupadas en el IV milenio aC. Sin embargo, enlas Baleares los datos sugieren la llegada de los primeros humanos en la segunda mitad, o tal vez elúltimo cuarto, del III milenio aC. Nos referimos a esta disparidad como la «paradoja balear»; ¿porqué fueron estas grandes islas colonizadas tan tarde? En esta contribución, contextualizamos losdatos de las Baleares y sugerimos que diversos factores de atracción y expulsión habrían afectado lavoluntad de las comunidades agropastoriles de tierra firme por emprender esfuerzos colonizadores.Consideramos necesario mejorar nuestra comprensión de los factores socioeconómicos, medioambientalesy climáticos en las posibles áreas de origen de las colonizaciones
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