We consider a broad class of interactions between radiation and a light scalar field, including both conformal and disformal couplings. Such a scalar field potentially acts on cosmological scales as dark energy and could also appear in modified gravi
ty theories. We study the consequences of these couplings on the mixing between the scalar field and photons in galaxy clusters in the presence of a magnetic field. In particular we focus on the resulting turbulence-induced irregularities in the X-ray and UV bands. We find new bounds on the photon-to-scalar couplings, both conformal and disformal, which complement laboratory experiments and other astrophysical constraints.
Axion-like particles are hypothetical new light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of ax
ion-like particles can modify the energy spectrum of the gamma rays. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac PKS 2155-304 are used to derive conservative upper limits on the strength of the axion-like particle coupling to photons. This study gives rise to the first exclusions on axion-like particles from gamma-ray astronomy. The derived constraints apply to both light pseudo-scalar and scalar bosons that couple to the electromagnetic field.
G. Galanti and M .Roncadelli recently made public some comments on the article by D. Wouters and P. Brun about irregularities induced by photon mixing to axion-like particles in astrophysical media [Phys. Rev. D86, 043005 (2012)]. They claim in parti
cular to have found some mistakes in the article. This note is a response to their comments, we refute their arguments and show that the results presented in the article are correct. It turns out most of the misunderstandings come from the definition of the beam initial state, some clarifications about which are given here.
The high-energy Universe is potentially a great laboratory for searching new light bosons such as axion-like particles (ALPs). Cosmic sources are indeed the scene of violent phenomena that involve strong magnetic field and/or very long baselines, whe
re the effects of the mixing of photons with ALPs could lead to observable effects. Two examples are archetypal of this fact, that are the Universe opacity to gamma-rays and the imprints of astrophysical magnetic turbulence in the energy spectra of high-energy sources. In the first case, hints for the existence of ALPs can be proposed whereas the second one is used to put constraints on the ALP mass and coupling to photons.
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, dwa
rf 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.
The presence of substructures in dark matter haloes is an unavoidable consequence of the cold dark matter paradigm. Indirect signals from these objects have been extensively searched for with cosmic rays and gamma-rays. At first sight, Cherenkov tele
scopes seem not very well suited for such searches, due to their small fields of view and the random nature of the possible dark matter substructure positions in the sky. However, with long enough exposure and an adequate observation strategy, the very good sensitivity of this experimental technique allows us to constrain particle dark matter models. We confront here the sensitivity map of the HESS experiment built out of their Galactic scan survey to the state-of-the-art cosmological N-body simulation Via Lactea II. We obtain competitive constraints on the annihilation cross section, at the level of 10^-24 -10^-23 cm^3s^-1. The results are extrapolated to the future Cherenkov Telescope Array, in the cases of a Galactic plane survey and of an even wider extragalactic survey. In the latter case, it is shown that the sensitivity of the Cherenkov Telescope Array will be sufficient to reach the most natural particle dark matter models.
Recent measurements of cosmic ray electrons and positrons by PAMELA, ATIC, Fermi and HESS have revealed interesting excesses and features in the GeV-TeV range. Many possible explanations have been suggested, invoking one or more nearby primary source
s such as pulsars and supernova remnants, or dark matter. Based on the output of the TANGO in PARIS --Testing Astroparticle with the New GeV/TeV Observations in Positrons And electRons : Identifying the Sources-- workshop held in Paris in May 2009, we review here the latest experimental results and we discuss some virtues and drawbacks of the many theoretical interpretations proposed so far.
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.
