2,713 research outputs found
Nuclear Cosmic Rays propagation in the Atmosphere
The transport of the nuclear cosmic ray flux in the atmosphere is studied and
the atmospheric corrections to be applied to the measurements are calculated.
The contribution of the calculated corrections to the accuracy of the
experimental results are discussed and evaluated over the kinetic energy range
10-10 GeV/n. The Boron (B) and Carbon (C) elements system is used as a
test case. It is shown that the required corrections become largely dominant at
the highest energies investigated. The results are discussed.Comment: Proc. of 30th International Cosmic Ray Conference, Merida, Mexico; 4
page
Spherical Jeans analysis for dark matter indirect detection in dwarf spheroidal galaxies - Impact of physical parameters and triaxiality
Dwarf spheroidal (dSph) galaxies are among the most promising targets for the
indirect detection of dark matter (DM) from annihilation and/or decay products.
Empirical estimates of their DM content - and hence the magnitudes of expected
signals - rely on inferences from stellar-kinematic data. However, various
kinematic analyses can give different results and it is not obvious which are
most reliable. Using extensive sets of mock data of various sizes (mimicking
'ultra-faint' and 'classical' dSphs) and an MCMC engine, here we investigate
biases, uncertainties, and limitations of analyses based on parametric
solutions to the spherical Jeans equation. For a variety of functional forms
for the tracer and DM density profiles, as well as the orbital anisotropy
profile, we examine reliability of estimates for the astrophysical J- and
D-factors for annihilation and decay, respectively. For large (N > 1000)
stellar-kinematic samples typical of 'classical' dSphs, errors tend to be
dominated by systematics, which can be reduced through the use of sufficiently
general and flexible functional forms. For small (N < 100) samples typical of
'ultrafaints', statistical uncertainties tend to dominate systematic errors and
flexible models are less necessary. We define an optimal strategy that would
mitigate sensitivity to priors and other aspects of analyses based on the
spherical Jeans equation. We also find that the assumption of spherical
symmetry can bias estimates of J (with the 95% credibility intervals not
encompassing the true J-factor) when the object is mildly triaxial (axis ratios
b/a = 0.8, c/a = 0.6). A concluding table summarises the typical error budget
and biases for the different sample sizes considered.Comment: 21 pages, 20 figures. Minor changes (several clarifications): match
the MNRAS accepted versio
Estimates on Green functions of second order differential operators with singular coefficients
We investigate the Green functions G(x,x^{\prime}) of some second order
differential operators on R^{d+1} with singular coefficients depending only on
one coordinate x_{0}. We express the Green functions by means of the Brownian
motion. Applying probabilistic methods we prove that when x=(0,{\bf x}) and
x^{\prime}=(0,{\bf x}^{\prime}) (here x_{0}=0) lie on the singular hyperplanes
then G(0,{\bf x};0,{\bf x}^{\prime}) is more regular than the Green function of
operators with regular coefficients.Comment: 16 page
Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most
attractive targets for indirect searches of dark matter. In this work, we
reconstruct the dark matter annihilation (J-factor) and decay profiles for the
newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis
of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we
find Reticulum II's J-factor to be among the largest of any Milky Way dSph. We
have checked the robustness of this result against several ingredients of the
analysis. Unless it suffers from tidal disruption or significant inflation of
its velocity dispersion from binary stars, Reticulum II may provide a unique
window on dark matter particle properties.Comment: 5 pages, 4 figures. Match the ApJL accepted versio
Principles of genome evolution in the Drosophila melanogaster species group.
That closely related species often differ by chromosomal inversions was discovered by Sturtevant and Plunkett in 1926. Our knowledge of how these inversions originate is still very limited, although a prevailing view is that they are facilitated by ectopic recombination events between inverted repetitive sequences. The availability of genome sequences of related species now allows us to study in detail the mechanisms that generate interspecific inversions. We have analyzed the breakpoint regions of the 29 inversions that differentiate the chromosomes of Drosophila melanogaster and two closely related species, D. simulans and D. yakuba, and reconstructed the molecular events that underlie their origin. Experimental and computational analysis revealed that the breakpoint regions of 59% of the inversions (17/29) are associated with inverted duplications of genes or other nonrepetitive sequences. In only two cases do we find evidence for inverted repetitive sequences in inversion breakpoints. We propose that the presence of inverted duplications associated with inversion breakpoint regions is the result of staggered breaks, either isochromatid or chromatid, and that this, rather than ectopic exchange between inverted repetitive sequences, is the prevalent mechanism for the generation of inversions in the melanogaster species group. Outgroup analysis also revealed evidence for widespread breakpoint recycling. Lastly, we have found that expression domains in D. melanogaster may be disrupted in D. yakuba, bringing into question their potential adaptive significance
Heavy Nuclei Enrichment of the Galactic Cosmic Rays at High Energy: Astrophysical Interpretation
A substantial increase of the mean logarithmic mass of galactic
cosmic rays {\em vs} energy has been observed . We study three effects that
could explain this trend i) different source spectra for protons and heavy
nuclei ii) a selective nuclear destruction in flight of heavies iii) a gradient
of the source number and chemical composition in the galactic disk.
We take advantage of the diffusive cosmic ray propagation model developed at
LAPTH to study specifically the geometrical aspects of the propagation and
extend it to high energy. Using a simple modeling of the spectral knee around
$10^{15}$ eV, a bump in appears. This feature is smoother when the
spectral index of protons is steeper than Fe's.
We analyze the effects of the rigidity dependence of the diffusion
coefficient and the scale height of the confinement halo and we show that is most sensitive to the first parameter. Pure geometrical effects are less
determining than the diffusion coefficient spectral index. Subsequently, we
conclude that the physics of cosmic ray confinement is the essential cause of
the heavy nuclei enrichment until eV.Comment: 26 pages, 7 PostScript figures. Astropart. Phys, accepted; misprint
in fig6 correcte
Kaluza-Klein Dark Matter and Galactic Antiprotons
Extra dimensions offer new ways to address long-standing problems in beyond
the standard model particle physics. In some classes of extra-dimensional
models, the lightest Kaluza-Klein particle is a viable dark matter candidate.
In this work, we study indirect detection of Kaluza-Klein dark matter via its
annihilation into antiprotons. We use a sophisticated galactic cosmic ray
diffusion model whose parameters are fully constrained by an extensive set of
experimental data. We discuss how fluxes of cosmic antiprotons can be used to
exclude low Kaluza-Klein masses.Comment: 14 pages, 7 figures, 3 table
- …