CNRS Paris Institute of Astrophysics
CNRS Paris Institute of Astrophysics
Allys E.,CNRS Paris Institute of Astrophysics
Physical Review D | Year: 2017
We investigate a new class of scalar multi-Galileon models, which is not included in the commonly admitted general formulation of generalized multi-Galileons. The Lagrangians of this class of models, some of them having already been introduced in previous works, are specific to multi-Galileon theories, and vanish in the single Galileon case. We examine them in detail, discussing in particular some hidden symmetry properties which can be made explicit by adding total derivatives to these Lagrangians. These properties allow us to describe the possible dynamics for these new Lagrangians in the case of multi-Galileons in the fundamental representation of a SO(N) and SU(N) global symmetry group, as well as in the adjoint representation of a SU(N) global symmetry group. We perform in parallel an exhaustive examination of some of these models, finding a complete agreement with the dynamics obtained using the symmetry properties. Finally, we conclude by discussing what could be the most general multi-Galileon theory, as well as the link between scalar and vector multi-Galileon models. © 2017 American Physical Society.
Arina C.,University of Amsterdam |
Arina C.,CNRS Paris Institute of Astrophysics |
Del Nobile E.,University of California at Los Angeles |
Panci P.,CNRS Paris Institute of Astrophysics
Physical Review Letters | Year: 2015
We study a Dirac dark matter particle interacting with ordinary matter via the exchange of a light pseudoscalar, and analyze its impact on both direct and indirect detection experiments. We show that this candidate can accommodate the long-standing DAMA modulated signal and yet be compatible with all exclusion limits at 99S% C.L. This result holds for natural choices of the pseudoscalar-quark couplings (e.g., flavor universal), which give rise to a significant enhancement of the dark matter-proton coupling with respect to the coupling to neutrons. We also find that this candidate can accommodate the observed 1-3 GeV gamma-ray excess at the Galactic center and at the same time have the correct relic density today. The model could be tested with measurements of rare meson decays, flavor changing processes, and searches for axionlike particles with mass in the MeV range. © 2015 American Physical Society.
Prantzos N.,CNRS Paris Institute of Astrophysics
Astronomy and Astrophysics | Year: 2012
Context. We reassess the problem of the production and evolution of the light elements Li, Be and B and of their isotopes in the Milky Way in the light of new observational and theoretical developments. Aims. The main novelty is the introduction of a new scheme for the origin of Galactic cosmic rays (GCR), which for the first time enables a self-consistent calculation of their composition during galactic evolution. Methods. The scheme accounts for key features of the present-day GCR source composition, it is based on the wind yields of the Geneva models of rotating, mass-losing stars and it is fully coupled to a detailed galactic chemical evolution code. Results. We find that the adopted GCR source composition accounts naturally for the observations of primary Be and helps understanding why Be follows Fe more closely than O. We find that GCR produce ∼70% of the solar 11B/ 10B isotopic ratio; the remaining 30% of 11B presumably result from ν-nucleosynthesis in massive star explosions. We find that GCR and primordial nucleosynthesis can produce at most ∼30% of solar Li. At least half of the solar Li has to originate in low-mass stellar sources (red giants, asymptotic giant branch stars, or novae), but the required average yields of those sources are found to be much higher than obtained in current models of stellar nucleosynthesis. We also present radial profiles of LiBeB elemental and isotopic abundances in the Milky Way disc. We argue that the shape of those profiles-and the late evolution of LiBeB in general-reveals important features of the production of those light elements through primary and secondary processes. © 2012 ESO.
Galli S.,CNRS Paris Institute of Astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
We propose a new method to probe for variations in the fine structure constant α using clusters of galaxies, opening up a window on a new redshift range for such constraints. Hot clusters shine in the x-ray mainly due to bremsstrahlung, while they leave an imprint on the cosmic microwave background (CMB) frequency spectrum through the Sunyaev-Zel'dovich effect. These two physical processes can be characterized by the integrated Comptonization parameter YSZDA2 and its x-ray counterpart, the YX parameter. The ratio of these two quantities is expected to be constant from numerical simulations and current observations. We show that this fact can be exploited to constrain α, as the ratio of the two parameters depends on the fine structure constant as â̂α3.5. We determine current constraints from a combination of Planck SZ and XMM-Newton data, testing different models of variation of α. When fitting for a constant value of α, we find that current constraints are at the 0.8% level, comparable with current CMB bounds. We discuss strategies for further improving these constraints by at least a factor ∼3. © 2013 American Physical Society.
Davis J.H.,CNRS Paris Institute of Astrophysics
Journal of Cosmology and Astroparticle Physics | Year: 2015
Future multi-tonne Direct Detection experiments will be sensitive to solar neutrino induced nuclear recoils which form an irreducible background to light Dark Matter searches. Indeed for masses around 6 GeV the spectra of neutrinos and Dark Matter are so similar that experiments are said to run into a neutrino floor, for which sensitivity increases only marginally with exposure past a certain cross section. In this work we show that this floor can be overcome using the different annual modulation expected from solar neutrinos and Dark Matter. Specifically for cross sections below the neutrino floor the DM signal is observable through a phase shift and a smaller amplitude for the time-dependent event rate. This allows the exclusion power to be improved by up to an order of magnitude for large exposures. In addition we demonstrate that, using only spectral information, the neutrino floor exists over a wider mass range than has been previously shown, since the large uncertainties in the Dark Matter velocity distribution make the signal spectrum harder to distinguish from the neutrino background. However for most velocity distributions it can still be surpassed using timing information, and so the neutrino floor is not an absolute limit on the sensitivity of Direct Detection experiments.
Alard C.,CNRS Paris Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013
This paper explores the self-similar solutions of the Vlasov-Poisson system and their relation to the gravitational collapse of dynamically cold systems. Analytic solutions are derived for power-law potentials in one dimension, and extensions of these solutions in three dimensions are proposed. Next, the self-similarity of the collapse of cold dynamical systems is investigated numerically. The fold system in phase space is consistent with analytic self-similar solutions, which present all the proper self-similar scaling. An additional point is the appearance of an x-1/2 law at the centre of the system for initial conditions with power-law index larger than -1/2(the Binney conjecture). It is found that the first appearance of the x-1/2 law corresponds to the formation of a singularity very close to the centre. Finally, the general properties of self-similar multidimensional solutions near equilibrium are investigated. Smooth and continuous self-similar solutions have power-law behaviour at equilibrium. However, cold initial conditions result in discontinuous phase-space solutions, and the smoothed phase-space density loses its auto-similar properties. This problem is easily solved by observing that the probability distribution of the phase-space density P is identical except for scaling parameters to the probability distribution of the smoothed phase-space density PS. As a consequence, PSinherits the self-similar properties of P. This particular property is at the origin of the universalpower law observed in numerical simulation for Ρ/Σ3. The self-similar properties of PS imply that other quantities should also have a universal power-law behaviour with predictable exponents. This hypothesis is tested using a numerical model of the phase-space density of cold dark matter haloes, and excellent agreement is obtained. © 2012 The Author.
Lemoine M.,CNRS Paris Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013
Microphysics of weakly magnetized relativistic collisionless shock waves, corroborated by recent high performance numerical simulations, indicates the presence of a microturbulent layer of large magnetic field strength behind the shockfront, which must decay beyond some hundreds of skin depths. This paper discusses the dynamics of such microturbulence, borrowing from these same numerical simulations, and calculates the synchrotron signature of a power law of shock accelerated particles. The decaying microturbulent layer is found to leave distinct signatures in the spectro-temporal evolution of the spectrum Fvαt-αV-β of a decelerating blast wave, which are potentially visible in early multiwavelength follow-up observations of gamma-ray bursts. This paper also discusses the influence of the evolving microturbulence on the acceleration process, with particular emphasis on the maximal energy of synchrotron afterglow photons, which falls in the GeV range for standard gamma-ray burst parameters. Finally, this paper argues that the evolving microturbulence plays a key role in shaping the spectra of recently observed gamma-ray bursts with extended GeV emission, such as GRB 090510. © 2012 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.
Blanchet L.,CNRS Paris Institute of Astrophysics
Living Reviews in Relativity | Year: 2014
To be observed and analyzed by the network of gravitational wave detectors on ground (LIGO, VIRGO, etc.) and by the future detectors in space (eLISA, etc.), inspiralling compact binaries-binary star systems composed of neutron stars and/or black holes in their late stage of evolution-require high-accuracy templates predicted by general relativity theory. The gravitational waves emitted by these very relativistic systems can be accurately modelled using a high-order post-Newtonian gravitational wave generation formalism. In this article, we present the current state of the art on post-Newtonian methods as applied to the dynamics and gravitational radiation of general matter sources (including the radiation reaction back onto the source) and inspiralling compact binaries. We describe the post-Newtonian equations of motion of compact binaries and the associated Lagrangian and Hamiltonian formalisms, paying attention to the self-field regularizations at work in the calculations. Several notions of innermost circular orbits are discussed. We estimate the accuracy of the post-Newtonian approximation and make a comparison with numerical computations of the gravitational selfforce for compact binaries in the small mass ratio limit. The gravitational waveform and energy flux are obtained to high post-Newtonian order and the binary's orbital phase evolution is deduced from an energy balance argument. Some landmark results are given in the case of eccentric compact binaries-moving on quasi-elliptical orbits with non-negligible eccentricity. The spins of the two black holes play an important role in the definition of the gravitational wave templates. We investigate their imprint on the equations of motion and gravitational wave phasing up to high post-Newtonian order (restricting to spin-orbit effects which are linear in spins), and analyze the post-Newtonian spin precession equations as well as the induced precession of the orbital plane.
Munoz Caro G.M.,CSIC - National Institute of Aerospace Technology |
Dartois E.,CNRS Paris Institute of Astrophysics
Chemical Society Reviews | Year: 2013
A compendium of different solid carbonaceous materials detected in space is presented, focussing on the search for organic matter of prebiotic interest. This journey takes us from the carbon grains likely formed in the atmospheres of evolved stars to organic grain mantles made from ice processing thought to be present in dense interstellar clouds and circumstellar regions, making a stop in solar system objects that could have delivered organic species to the early Earth. The most abundant carbon materials detected to date in space appear to be of little biological relevance. On the other hand, organic refractory residues, made in the laboratory from UV-photoprocessing followed by warm-up of interstellar ice analogs, are a hydrocarbon material rich in O and N containing chemical compounds that could act as initiators of prebiotic chemistry. A similar material might be present in dust grains inside dense clouds or circumstellar regions, some comets, and as a minor component in carbonaceous chondrites. We use infrared spectroscopy as a tool to spot organic refractory matter in various space environments. The delivery of organic materials via comets, (micro-) meteorites, and interplanetary dust particles to the primitive Earth might have contributed as a starting material for prebiotic chemistry. To test this hypothesis, it is first essential to characterize the composition of exogenous organic matter. This journal is © The Royal Society of Chemistry.
Sousbie T.,University of Tokyo |
Sousbie T.,CNRS Paris Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011
We present DisPerSE, a novel approach to the coherent multiscale identification of all types of astrophysical structures, in particular the filaments, in the large-scale distribution of the matter in the Universe. This method and the corresponding piece of software allows for a genuinely scale-free and parameter-free identification of the voids, walls, filaments, clusters and their configuration within the cosmic web, directly from the discrete distribution of particles in N-body simulations or galaxies in sparse observational catalogues. To achieve that goal, the method works directly over the Delaunay tessellation of the discrete sample and uses the Delaunay tessellation field estimator density computed at each tracer particle; no further sampling, smoothing or processing of the density field is required. The idea is based on recent advances in distinct subdomains of the computational topology, namely the discrete Morse theory which allows for a rigorous application of topological principles to astrophysical data sets, and the theory of persistence, which allows us to consistently account for the intrinsic uncertainty and Poisson noise within data sets. Practically, the user can define a given persistence level in terms of robustness with respect to noise (defined as a 'number of σ') and the algorithm returns the structures with the corresponding significance as sets of critical points, lines, surfaces and volumes corresponding to the clusters, filaments, walls and voids - filaments, connected at cluster nodes, crawling along the edges of walls bounding the voids. From a geometrical point of view, the method is also interesting as it allows for a robust quantification of the topological properties of a discrete distribution in terms of Betti numbers or Euler characteristics, without having to resort to smoothing or having to define a particular scale. In this paper, we introduce the necessary mathematical background and describe the method and implementation, while we address the application to 3D simulated and observed data sets in the companion paper (Sousbie, Pichon & Kawahara, Paper II). © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.