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Bernardeau F.,CEA Saclay Nuclear Research Center | Bernardeau F.,French National Center for Scientific Research | Crocce M.,Institute Of Ciencies Of Lespai | Scoccimarro R.,New York University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We present a new scheme for the general computation of cosmic propagators that allow to interpolate between standard perturbative results at low k and their expected large-k resummed behavior. This scheme is applicable to any multipoint propagator and allows the matching of perturbative low-k calculations to any number of loops to their large-k behavior, and can potentially be applied in case of nonstandard cosmological scenarios such as those with non-Gaussian initial conditions. The validity of our proposal is checked against previous prescriptions and measurements in numerical simulations showing a remarkably good agreement. Such a generic prescription for multipoint propagators provides the necessary building blocks for the computation of polyspectra in the context of the so-called Γ expansion introduced by F. Bernardeau, M. Crocce, and R. ScoccimarroPhys. Rev. DPRVDAQ1550-7998 78, 103521 (2008).10.1103/PhysRevD.78.103521. As a concrete application we present a consistent calculation of the matter bispectrum at one-loop order. © 2012 American Physical Society. Source

Bonnett C.,Institute Of Ciencies Of Lespai | Bonnett C.,Autonomous University of Barcelona
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present a novel way of using neural networks (NN) to estimate the redshift distribution of a galaxy sample. We are able to obtain a probability density function (PDF) for each galaxy using a classification NN. The method is applied to 58 714 galaxies in CFHTLenS that have spectroscopic redshifts from DEEP2, VVDS and VIPERS. Using this data, we show that the stacked PDFs give an excellent representation of the true N(z) using information from 5, 4 or 3 photometric bands. We show that the fractional error due to using N(zphot) instead of N(ztruth) is ≤1 per cent on the lensing power spectrum (Pκ ) in several tomographic bins. Further, we investigate how well this method performs when few training samples are available and show that in this regime the NN slightly overestimates the N(z) at high z. Finally, the case where the training sample is not representative of the full data set is investigated. © 2015 The Authors. Source

Hernanz M.,Institute Of Ciencies Of Lespai
Bulletin of the Astronomical Society of India | Year: 2012

Classical novae produce radioactive nuclei which are emitters of γ-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission (511 keV line and a continuum below this energy, with a cut-off at 20-30 keV). The analysis of γ-ray spectra and light curves is potentially a unique and powerful tool both to trace the corresponding isotopes and to give insights on the properties of the expanding envelope determining its transparency. Another possible origin of γ-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce γ-rays of energies larger than 100 MeV. MeV photons during nova explosions have not been detected yet, although several attempts have been made in the last decades; on the other hand, GeV photons from novae have been detected in some particular novae, in symbiotic binaries, where the companion is a red giant with a wind, instead of a main sequence star as in the cataclysmic variables hosting classical novae. Both mechanisms of γ-ray production in novae are reviewed, with more emphasis on the one related to radioactivities. Source

Amaro-Seoane P.,Max Planck Institute For Gravitationsphysik Albert Einstein Institute | Amaro-Seoane P.,Institute Of Ciencies Of Lespai | Santamaria L.,Max Planck Institute For Gravitationsphysik Albert Einstein Institute
Astrophysical Journal | Year: 2010

Even though the existence of intermediate-mass black holes (IMBHs; black holes with masses ranging between 102 M⊙ and 104 M⊙) has not yet been corroborated observationally, these objects are of high interest for astrophysics. Our understanding of the formation and evolution of supermassive black holes, as well as galaxy evolution modeling and cosmography would dramatically change if an IMBH were to be observed. From the point of view of traditional photon-based astronomy, which relies on the monitoring of innermost stellar kinematics, the direct detection of an IMBH seems to be rather far in the future. However, the prospect of the detection and characterization of an IMBH has good chances in lower frequency gravitational-wave (GW) astrophysics using ground-based detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, and the future Einstein Telescope (ET). We present an analysis of the signal of a system of a binary of IMBHs based on a waveform model obtained with numerical relativity simulations coupled with post-Newtonian calculations at the highest available order. IMBH binaries with total masses between 200 and 20,000 M⊙ would produce significant signal-to-noise ratios in Advanced LIGO and Virgo and the ET. We have computed the expected event rate of IMBH binary coalescences for different configurations of the binary, finding interesting values that depend on the spin of the IMBHs. The prospects for IMBH detection and characterization with ground-based GW observatories would not only provide us with a robust test of general relativity, but would also corroborate the existence of these systems. Such detections should allow astrophysicists to probe the stellar environments of IMBHs and their formation processes. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. Source

Bernardeau F.,CEA Saclay Nuclear Research Center | Crocce M.,Institute Of Ciencies Of Lespai | Sefusatti E.,CEA Saclay Nuclear Research Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We show here how renormalized perturbation theory calculations applied to the quasilinear growth of the large-scale structure can be carried on in presence of primordial non-Gaussian (PNG) initial conditions. It is explicitly demonstrated that the series reordering scheme proposed in Bernardeau, Crocce, and Scoccimarro [Phys. Rev. D 78, 103521 (2008)] is preserved for non-Gaussian initial conditions. This scheme applies to the power spectrum and higher-order spectra and is based on a reorganization of the contributing terms into the sum of products of multipoint propagators. In case of PNG, new contributing terms appear, the importance of which is discussed in the context of current PNG models. The properties of the building blocks of such resummation schemes, the multipoint propagators, are then investigated. It is first remarked that their expressions are left unchanged at one-loop order irrespective of statistical properties of the initial field. We furthermore show that the high-momentum limit of each of these propagators can be explicitly computed even for arbitrary initial conditions. They are found to be damped by an exponential cutoff whose expression is directly related to the moment generating function of the one-dimensional displacement field. This extends what had been established for multipoint propagators for Gaussian initial conditions. Numerical forms of the cutoff are shown for the so-called local model of PNG. © 2010 The American Physical Society. Source

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