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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. Source


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. Source


Wojtak R.,Copenhagen University | Mamon G.A.,CNRS Paris Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the kinematics of satellites around isolated galaxies selected from the Sloan Digital Sky Survey spectroscopic catalogue. Using a model of the phase-space density previously measured for the haloes of Λ cold dark matter (ΛCDM) cosmological simulations, we determine the properties of the halo mass distribution and the orbital anisotropy of the satellites as a function of the colour-based morphological type and the stellar mass of the central host galaxy. We place constraints on the halo mass and the concentration parameter of dark matter and the satellite number density profiles. We obtain a concentration-mass relation for galactic dark matter haloes that is consistent with predictions of a standard ΛCDM cosmological model. At a given halo or stellar mass, red galaxies have more concentrated haloes than their blue counterparts. The fraction of dark matter within a few effective radii is minimal for 11.25 < log10(M*/M⊙)<11.5. The number density profile of the satellites appears to be shallower than that of dark matter, with the scale radius typically 60 per cent larger than that of dark matter. The orbital anisotropy around red hosts exhibits a mild excess of radial motions, in agreement with the typical anisotropy profiles found in cosmological simulations, whereas blue galaxies are found to be consistent with an isotropic velocity distribution. Our new constraints on the halo masses of galaxies are used to provide analytic approximations of the halo-stellar mass relation for red and blue galaxies. © 2012 The Authors. Source


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. Source


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. Source

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