Galactic secondary positron flux at the Earth

Secondary positrons are produced by spallation of cosmic rays within the interstellar gas. Measurements have been typically expressed in terms of the positron fraction, which exhibits an increase above 10 GeV. Many scenarios have been proposed to explain this feature, among them some additional primary positrons originating from dark matter annihilation in the Galaxy. The PAMELA satellite has provided high quality data that has enabled high accuracy statistical analyses to be made, showing that the increase in the positron fraction extends up to about 100 GeV. It is therefore of paramount importance to constrain theoretically the expected secondary positron flux to interpret the observations in an accurate way. We find the secondary positron flux to be reproduced well by the available observations, and to have theoretical uncertainties that we quantify to be as large as about one order of magnitude. We also discuss the positron fraction issue and find that our predictions may be consistent with the data taken before PAMELA. For PAMELA data, we find that an excess is probably present after considering uncertainties in the positron flux, although its amplitude depends strongly on the assumptions made in relation to the electron flux. By fitting the current electron data, we show that when considering a soft electron spectrum, the amplitude of the excess might be far lower than usually claimed. We provide fresh insights that may help to explain the positron data with or without new physical model ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow stronger constraints to be aplaced on the cosmic--ray transport parameters, and are likely to reduce drastically the theoretical uncertainties.Comment: 15 pages, 12 figures. The recent PAMELA data on the positron fraction (arXiv:0810.4995) have been included and the ensuing discussion has been extended. Accepted version in A&

The effect of rotation and tidal heating on the thermal lightcurves of Super Mercuries

Short period (<50 days) low-mass (<10Mearth) exoplanets are abundant and the few of them whose radius and mass have been measured already reveal a diversity in composition. Some of these exoplanets are found on eccentric orbits and are subjected to strong tides affecting their rotation and resulting in significant tidal heating. Within this population, some planets are likely to be depleted in volatiles and have no atmosphere. We model the thermal emission of these "Super Mercuries" to study the signatures of rotation and tidal dissipation on their infrared light curve. We compute the time-dependent temperature map at the surface and in the subsurface of the planet and the resulting disk-integrated emission spectrum received by a distant observer for any observation geometry. We calculate the illumination of the planetary surface for any Keplerian orbit and rotation. We include the internal tidal heat flow, vertical heat diffusion in the subsurface and generate synthetic light curves. We show that the different rotation periods predicted by tidal models (spin-orbit resonances, pseudo-synchronization) produce different photometric signatures, which are observable provided that the thermal inertia of the surface is high, like that of solid or melted rocks (but not regolith). Tidal dissipation can also directly affect the light curves and make the inference of the rotation more difficult or easier depending on the existence of hot spots on the surface. Infrared light curve measurement with the James Webb Space Telescope and EChO can be used to infer exoplanets' rotation periods and dissipation rates and thus to test tidal models. This data will also constrain the nature of the (sub)surface by constraining the thermal inertia.Comment: 15 pages, 13 figures, accepted for publication in Astronomy & Astrophysic

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

Young star clusters as gamma ray emitters and their detection with Cherenkov Telescopes

Young massive star clusters as sites of strong stellar winds and supernova explosions may accelerate charged particles at high energies and produce gamma-rays. These sources may also contribute to the production of cosmic rays in our galaxy. At TeV energies several candidates have already been detected: Cygnus OB2, Westerlund 1 \& 2, W43, Pismis 22 and W49A. Our study addresses the issue of very young star clusters where no supernova has occurred yet. During the lifetime of a massive star (M$> 20 M_{\odot}$), supersonic stellar winds do indeed release as much energy as a supernova explosion. As supernova remnants are already known as gamma-ray emitters our purpose is to avoid any ambiguity on the origin of a possible gamma ray emission and to fully assume a stellar wind contribution. In this work we first present a catalogue of potential gamma-ray emitting clusters and discuss the criteria used to built the catalogue. We hence model the expected energetic particle spectrum including escapes and losses. We deduce gamma-ray luminosities produced by Inverse Compton and pion decay emission of each cluster and their associated HII regions. We finally compare these gamma-ray luminosities with HESS-II and CTA Cherenkov telescopes sensitivities

Secondary Cosmic Ray Nuclei from Supernova Remnants and Constraints to the Propagation Parameters

The secondary-to-primary B/C ratio is widely used to study the cosmic ray (CR) propagation processes in the Galaxy. It is usually assumed that secondary nuclei such as Li-Be-B are entirely generated by collisions of heavier CR nuclei with the interstellar medium (ISM). We study the CR propagation under a scenario where secondary nuclei can also be produced or accelerated from galactic sources. We consider the processes of hadronic interactions inside supernova remnants (SNRs) and re-acceleration of background CRs in strong shocks. Thus, we investigate their impact in the propagation parameter determination within present and future data. The spectra of Li-Be-B nuclei emitted from SNRs are harder than those due to CR collisions with the ISM. The secondary-to-primary ratios flatten significantly at ~TeV/n energies, both from spallation and re-acceleration in the sources. The two mechanisms are complementary to each other and depend on the properties of the local ISM around the expanding remnants. The secondary production in SNRs is significant for dense background media, n ~1 cm^-3, while the amount of re-accelerated CRs is relevant for SNRs expanding into rarefied media, n ~0.1 cm-3. Due to these effects, the the diffusion parameter 'delta' may be misunderstood by a factor of ~5-15%. Our estimations indicate that an experiment of the AMS-02 caliber can constrain the key propagation parameters while breaking the source-transport degeneracy, for a wide class of B/C-consistent models. Given the precision of the data expected from on-going experiments, the SNR production/acceleration of secondary nuclei should be considered, if any, to prevent a possible mis-determination of the CR transport parameters.Comment: 13 pages, 9 figures; matches the published versio

Dark Matter and LHC: What is the Connection?

We review what can (and cannot) be learned if dark matter is detected in one or more experiments, emphasizing the importance of combining LHC data with direct, astrophysical and cosmological probes of dark matter. We briefly review the conventional picture of a thermally produced WIMP relic density and its connection with theories of electroweak symmetry breaking. We then discuss both experimental and theoretical reasons why one might generically expect this picture to fail. If this is the case, we argue that a combined effort bringing together all types of data -- combined with explicitly constructed theoretical models -- will be the only way to achieve a complete understanding of the dark matter in our universe and become confident that any candidate actually provides the relic density.Comment: 25 pages, 2 figures, Invited review for Modern Physics Letters

Translation Representations and Scattering By Two Intervals

Studying unitary one-parameter groups in Hilbert space (U(t),H), we show that a model for obstacle scattering can be built, up to unitary equivalence, with the use of translation representations for L2-functions in the complement of two finite and disjoint intervals. The model encompasses a family of systems (U (t), H). For each, we obtain a detailed spectral representation, and we compute the scattering operator, and scattering matrix. We illustrate our results in the Lax-Phillips model where (U (t), H) represents an acoustic wave equation in an exterior domain; and in quantum tunneling for dynamics of quantum states