On the Dark Matter Solutions to the Cosmic Ray Lepton Puzzle

Recent measurements of cosmic ray leptons by PAMELA, ATIC, HESS and Fermi revealed interesting excesses. Many authors suggested particle Dark Matter (DM) annihilations could be at the origin of these effects. In this paper, we critically assess this interpretation by reviewing some results questioning the naturalness and robustness of such an interpretation. Natural values for the DM particle parameters lead to a poor leptons production so that models often require signal enhancement effects that we constrain here. Considering DM annihilations are likely to produce antiprotons as well, we use the PAMELA antiproton to proton ratio measurements to constrain a possible exotic contribution. We also consider the possibility of an enhancement due to a nearby clump of DM. This scenario appears unlikely when compared to the state-of-the-art cosmological N-body simulations. We conclude that the bulk of the observed signals most likely has no link with DM and is rather a new, yet unconsidered source of background for searches in these channels.Comment: 8 pages, Proceedings of the Invisible Universe International Conference 2009, Pari

Seeking particle dark matter in the TeV sky

Under the assumption that dark matter is made of new particles, annihilations of those are required to reproduce the correct dark matter abundance in the Universe. This process can occur in dense regions of our Galaxy such as the Galactic center, dwarf galaxies and other types of sub-haloes. High-energy gamma-rays are expected to be produced in dark matter particle collisions and could be detected by ground-based Cherenkov telescopes such as HESS, MAGIC and VERITAS. The main experimental challenges to get constraints on particle dark matter models are reviewed, making explicit the pros and cons that are inherent to this technique, together with the current results from running observatories. Main results concerning dark matter searches towards selected targets with Cherenkov telescopes are presented. Eventually, a focus is made on a new way to perform a search for Galactic subhaloes with such telescopes, based on wide-field surveys, as well as future prospects.Comment: 12 pages, 10 figures. To appear in the proceedings of the eleventh international symposium Frontiers of Fundamental Physic

Limits on Lorentz invariance violation at the Planck energy scale from H.E.S.S. spectral analysis of the blazar Mrk 501

Some extensions to the Standard Model lead to the introduction of Lorentz symmetry breaking terms, expected to induce deviations from Lorentz symmetry around the Planck scale. A parameterization of effects due to Lorentz invariance violation (LIV) can be introduced by adding an effective term to the photon dispersion relation. This affects the kinematics of electron-positron pair creation by TeV $\gamma$ rays on the extragalactic background light (EBL) and translates into modifications of the standard EBL opacity for the TeV photon spectra of extragalactic sources. Exclusion limits are presented, obtained with the spectral analysis of H.E.S.S. observations taken on the blazar Mrk 501 during the exceptional 2014 flare. The energy spectrum, extending very significantly above 10 TeV, allows to place strong limits on LIV in the photon sector at the level of the Planck energy scale for linear perturbations in the photon dispersion relation, and provides the strongest constraints presently for the case of quadratic perturbations.Comment: To appear in proceedings of the 6th Roma International Conference on Astro-Particle Physics (RICAP 16

Irregularity in gamma ray source spectra as a signature of axionlike particles

Oscillations from high energy photons into light pseudoscalar particles in an external magnetic field are expected to occur in some extensions of the standard model. It is usually assumed that those axionlike particles (ALPs) could produce a drop in the energy spectra of gamma ray sources and possibly decrease the opacity of the Universe for TeV gamma rays. We show here that these assumptions are in fact based on an average behavior that cannot happen in real observations of single sources. We propose a new method to search for photon-ALP oscillations, taking advantage of the fact that a single observation would deviate from the average expectation. Our method is based on the search for irregularities in the energy spectra of gamma ray sources. We predict features that are unlikely to be produced by known astrophysical processes and a new signature of ALPs that is easily falsifiable.Comment: 6 pages, 3 figures, matches accepted version, improved discussion on magnetic field models in v