Publications (78)285.53 Total impact
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ABSTRACT: We present a comprehensive derivation of linear perturbation equations for different matter species, including photons, baryons, cold dark matter, scalar fields, massless and massive neutrinos, in the presence of a generic conformal coupling. Starting from the Lagrangians, we show how the conformal transformation affects the dynamics. In particular, we discuss how to incorporate consistently the scalar coupling in the equations of the Boltzmann hierarchy for massive neutrinos and the subsequent fluid approximations. We use the recently proposed Kmouflage model as an example to demonstrate the numerical implementation of our linear perturbation equations. Kmouflage is a new mechanism to suppress the fifth force between matter particles induced by the scalar coupling, but in the linear regime the fifth force is unsuppressed and can change the clustering of different matter species in different ways. We show how the CMB, lensing potential and matter power spectra are affected by the fifth force, and find ranges of Kmouflage parameters whose effects could be seen observationally. We also find that the scalar coupling can have the nontrivial effect of shifting the amplitude of the power spectra of the lensing potential and density fluctuations in opposite directions, although both probe the overall clustering of matter. This paper can serve as a reference for those who work on generic coupled scalar field cosmology, or those who are interested in the cosmological behaviour of the Kmouflage model.11/2014;  [Show abstract] [Hide abstract]
ABSTRACT: This paper presents 52 Xray bright galaxy clusters selected within the 11 deg$^2$ XMMLSS survey. 51 of them have spectroscopic redshifts ($0.05<z<1.06$), one is identified at $z_{\rm phot}=1.9$, and all together make the highpurity "Class 1" (C1) cluster sample of the XMMLSS, the highest density sample of Xray selected clusters with a monitored selection function. Their Xray fluxes, averaged gas temperatures (median $T_X=2$ keV), luminosities (median $L_{X,500}=5\times10^{43}$ ergs/s) and total mass estimates (median $5\times10^{13} h^{1} M_{\odot}$) are measured, adapting to the specific signaltonoise regime of XMMLSS observations. The redshift distribution of clusters shows a deficit of sources when compared to the cosmological expectations, regardless of whether WMAP9 or Planck2013 CMB parameters are assumed. This lack of sources is particularly noticeable at $0.4 \lesssim z \lesssim 0.9$. However, after quantifying uncertainties due to small number statistics and sample variance we are not able to put firm (i.e. $>3 \sigma$) constraints on the presence of a large void in the cluster distribution. We work out alternative hypotheses and demonstrate that a negative redshift evolution in the normalization of the $L_{X}T_X$ relation (with respect to a selfsimilar evolution) is a plausible explanation for the observed deficit. We confirm this evolutionary trend by directly studying how C1 clusters populate the $L_{X}T_Xz$ space, properly accounting for selection biases. We point out that a systematically evolving, unresolved, central component in clusters and groups (AGN contamination or cool core) can impact the classification as extended sources and be partly responsible for the observed redshift distribution.[abridged]08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the smallscale static configurations of Kmouflage models defined by a general function $K(\chi)$ of the kinetic terms. The fifth force is screened by the nonlinear Kmouflage mechanism if $K'(\chi)$ grows sufficiently fast for large negative $\chi$. In the general nonspherically symmetric case, the fifth force is not aligned with the Newtonian force. For spherically symmetric static matter density profiles, the results depend on the potential function $W_{}(y) = y K'(y^2/2)$, which must be monotonically increasing to $+\infty$ for $y \geq 0$ to guarantee the existence of a single solution throughout space for any matter density profile. Starting from vanishing initial conditions or from nearby profiles, we numerically check that the scalar field converges to the static solution. If $W_{}$ is bounded, for highdensity objects there are no static solutions throughout space, but one can still define a static solution restricted to large radii. Our dynamical study shows that the scalar field relaxes to this static solution at large radii, whereas spatial gradients keep growing with time at smaller radii. If $W_{}$ is not bounded but nonmonotonic, there are an infinite number of discontinuous static solutions but these are not physical and those models are not theoretically sound. Such Kmouflage scenarios provide an example of theories that can appear viable at the cosmological level, for the cosmological background and perturbative analysis, while being meaningless at a nonlinear level for small scale configurations. This shows the importance of smallscale nonlinear analysis of screening models.Physical Review D 08/2014; 90(12). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The clustering ratio $\eta$, a largescale structure observable originally devised to constrain the shape of the power spectrum of matter density fluctuations, is shown to provide a sensitive and model independent probe of the nature of gravity in the cosmological regime. We apply this analysis to $F(R)$ theories of gravity using the luminous red galaxy sample extracted from the Sloan Digital Sky Survey. We find that the absolute amplitude of deviations from GR, $f_{R_0 }$, is constrained to be smaller than $3 \times 10^{6}$ at the 1$\sigma$ confidence level. This bound, improving by an order of magnitude on current constraints, makes cosmological probes of gravity competitive with Solar system tests.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We study the cosmology of Kmouflage theories at the background level. We show that the effects of the scalar field are suppressed at high matter density in the early Universe and only play a role in the late time Universe where the deviations of the Hubble rate from its $\Lambda$CDM counterpart can be of order five percent for redshifts $1 \lesssim z \lesssim 5$. Similarly, we find that the equation of state can cross the phantom divide in the recent past and even diverge when the effective scalar energy density goes negative and subdominant compared to matter, preserving the positivity of the squared Hubble rate. These features are present in models for which Big Bang Nucleosynthesis is not affected. We analyse the fate of Kmouflage when the nonlinear kinetic terms give rise to ghosts, particle excitations with negative energy. In this case, we find that the Kmouflage theories can only be considered as an effective description of the Universe at low energy below $1$ keV. In the safe ghostfree models, we find that the equation of state always diverges in the past and changes significantly by a few percent since $z\lesssim 1$.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We study structure formation in Kmouflage cosmology whose main feature is the absence of screening effect on quasilinear scales. We show that the growth of structure at the linear level is both affected by a new time dependent Newton constant and a friction term which depend on the background evolution. These combine with the modified background evolution to change the growth rate by up to ten percent since $z\sim 2$. At the one loop level, we find that the nonlinearities of the Kmouflage models are mostly due to the matter dynamics and that the scalar perturbations can be treated at tree level. We also study the spherical collapse in Kmouflage models and show that the critical density contrast deviates from its $\Lambda$CDM value and that, as a result, the halo mass function is modified for large masses by an order one factor. Finally we consider the deviation of the matter spectrum from $\Lambda$CDM on nonlinear scales where a halo model is utilised. We find that the discrepancy peaks around $1\ h{\rm Mpc}^{1}$ with a relative difference which can reach fifty percent. Importantly, these features are still true at larger redshifts, contrary to models of the chameleon$f(R)$ and Galileon types.Physical Review D 03/2014; 90(2). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We explicitly test the equaltime consistency relation between the angularaveraged bispectrum and the power spectrum of the matter density field, employing a large suite of cosmological $N$body simulations. This is the lowestorder version of the relations between $(\ell+n)$point and $n$point polyspectra, where one averages over the angles of $\ell$ soft modes. This relation depends on two wave numbers, $k'$ in the soft domain and $k$ in the hard domain. We show that it holds up to a good accuracy, when $k'/k\ll 1$ and $k'$ is in the linear regime, while the hard mode $k$ goes from linear ($0.1\,h\,\mathrm{Mpc}^{1}$) to nonlinear ($1.0\,h\,\mathrm{Mpc}^{1}$) scales. On scales $k\lesssim 0.4\,h\,\mathrm{Mpc}^{1}$, we confirm the relation within a $\sim 5\%$ accuracy, even though the bispectrum can already deviate from leadingorder perturbation theory by more than $30\%$. We further show that the relation extends up to nonlinear scales, $k \sim 1.0\,h\,\mathrm{Mpc}^{1}$, within an accuracy of $\sim 10\%$.Physical Review D 02/2014; 90(2). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Aims: We estimate the amplitude of the sourcelens clustering bias and of the intrinsicalignment bias of weaklensing estimators of the twopoint and threepoint convergence and cosmicshear correlation functions. Methods: We use a linear galaxy bias model for the galaxydensity correlations, as well as a linear intrinsicalignment model. For the threepoint and fourpoint density correlations, we use analytical or semianalytical models, based on a hierarchical ansatz or a combination of oneloop perturbation theory with a halo model. Results: For twopoint statistics, we find that the sourcelens clustering bias is typically several orders of magnitude below the weaklensing signal, except when we correlate a very lowredshift galaxy (z2 ≲ 0.05) with a higher redshift galaxy (z1 ≳ 0.5), where it can reach 10% of the signal for the shear. For threepoint statistics, the sourcelens clustering bias is typically on the order of 10% of the signal, as soon as the three galaxy source redshifts are not identical. The intrinsicalignment bias is typically about 10% of the signal for both twopoint and threepoint statistics. Thus, both sourcelens clustering bias and intrinsicalignment bias must be taken into account for threepoint estimators aiming at a better than 10% accuracy. Appendices are available in electronic form at http://www.aanda.orgAstronomy and Astrophysics 01/2014; · 4.48 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The cosmological dynamics of gravitational clustering satisfies an approximate invariance with respect to the cosmological parameters that is often used to simplify analytical computations. We describe how this approximate symmetry gives rise to angular averaged consistency relations for the matter density correlations. This allows one to write the $(\ell+n)$ density correlation, with $\ell$ largescale linear wave numbers that are integrated over angles, and $n$ fixed smallscale nonlinear wave numbers, in terms of the smallscale $n$point density correlation and $\ell$ prefactors that involve the linear power spectra at the largescale wave numbers. These relations, which do not vanish for equaltime statistics, go beyond the already known kinematic consistency relations. They could be used to detect primordial nonGaussianities, modifications of gravity, limitations of galaxy biasing schemes, or to help designing analytical models of gravitational clustering.Physical Review D 11/2013; 89(12). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We describe how the kinematic consistency relations satisfied by density correlations of the largescale structures of the Universe can be derived within the usual Newtonian framework. These relations express a kinematic effect and show how the $(\ell+n)$density correlation factors in terms of the $n$point correlation and $\ell$ linear power spectrum factors, in the limit where the $\ell$ soft wave numbers become linear and much smaller than the $n$ other wave numbers. We show how these relations extend to multifluid cases. These consistency relations are not equivalent to the Galilean invariance nor to the equivalence principle, as both can be violated and the relations remain valid. We describe how these relations are due to a weak form of scale separation and that a detection of their violation would indicate nonGaussian initial conditions or a modification of gravity that does not converge to General Relativity on large scales.Physical Review D 11/2013; 89(8). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the possible accuracy that can be reached by analytical models for the matter density power spectrum and correlation function. Using a realistic description of the power spectrum that combines perturbation theory with a halo model, we study the convergence rate of several perturbative expansion schemes and the impact of nonperturbative effects, as well as the sensitivity to phenomenological halo parameters. We check that the simple reorganization of the standard perturbative expansion, with a Gaussian damping prefactor, provides a wellordered convergence and a finite correlation function that yields a percent accuracy at the BAO peak (as soon as one goes to second order). Lagrangianspace expansions are somewhat more efficient, when truncated at low orders, but may diverge at high orders. We find that whereas the uncertainty on the haloprofile massconcentration relation is not a strong limitation, the uncertainty on the halo mass function can severely limit the accuracy of theoretical predictions for $P(k)$. The realspace correlation function provides a better separation between perturbative and nonperturbative effects, which are restricted to $x \lesssim 10 h^{1}$Mpc at all redshifts.Physical Review D 08/2013; 88(8). · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the effects of screened modified gravity of the $f(R)$, dilaton and symmetron types on structure formation, from the quasilinear to the nonlinear regime, using semianalytical methods. For such models, where the range of the new scalar field is typically within the Mpc range and below in the cosmological context, nonlinear techniques are required to understand the deviations of the power spectrum of the matter density contrast compared to the $\Lambda$CDM template. This is nowadays commonly tackled using extensive Nbody simulations. Here we present new results combining exact perturbation theory at the one loop level (and a partial resummation of the perturbative series) with a halo model. The former allows one to extend the linear perturbative analysis up to $k\lesssim 0.15{\rm h Mpc}^{1}$ at the perturbative level while the latter leads to a reasonable, up to a few percent, agreement with numerical simulations for $k\lesssim 3{\rm h Mpc}^{1}$ for large curvature $f(R)$ models, and $k\lesssim 1{\rm h Mpc}^{1}$ for dilatons and symmetrons, at $z=0$. We also discuss how the behaviors of the perturbative expansions and of the spherical collapse differ for $f(R)$, dilaton, and symmetron models.Physical review D: Particles and fields 05/2013; 88(2).  [Show abstract] [Hide abstract]
ABSTRACT: We present a new approach to computing the matter density power spectrum, from large linear scales to small highly nonlinear scales. Instead of explicitly computing a partial series of highorder diagrams, as in perturbative resummation schemes, we embed the standard perturbation theory within a realistic nonlinear Lagrangianspace ansatz. We also point out that an "adhesionlike" regularization of the shellcrossing regime is more realistic than a "Zel'dovichlike" behavior, where particles freely escape to infinity. This provides a "cosmic web" power spectrum with good smallscale properties that provide a good matching with a halo model on mildly nonlinear scales. We obtain a good agreement with numerical simulations on large scales, better than 3% for $k\leq 1 h$Mpc$^{1}$, and on small scales, better than 10% for $k \leq 10 h$Mpc$^{1}$, at $z \geq 0.35$, which improves over previous methods.Physical review D: Particles and fields 02/2013; 87(8).  [Show abstract] [Hide abstract]
ABSTRACT: We investigate whether the latetime (at $z\leq 100$) velocity dispersion expected in Warm Dark Matter scenarios could have some effect on the cosmic web (i.e., outside of virialized halos). We consider effective hydrodynamical equations, with a pressurelike term that agrees at the linear level with the analysis of the Vlasov equation. Then, using analytical methods, based on perturbative expansions and the spherical dynamics, we investigate the impact of this term for a 1 keV dark matter particle. We find that the latetime velocity dispersion has a negligible effect on the power spectrum on perturbative scales and on the halo mass function. However, it has a significant impact on the probability distribution function of the density contrast at $z \sim 3$ on scales smaller than $0.1 h^{1}$Mpc, which correspond to Lyman$\alpha$ clouds. Finally, we note that numerical simulations should start at $z_i\geq 100$ rather than $z_i \leq 50$ to avoid underestimating gravitational clustering at low redshifts.Physical review D: Particles and fields 06/2012; 86(12).  [Show abstract] [Hide abstract]
ABSTRACT: We study the growth of structures in modified gravity models where the Poisson equation and the relationship between the two Newtonian potentials are modified by explicit functions of space and time. This parameterisation applies to the $f(R)$ models and more generally to screened modified gravity models. We investigate the linear and weakly nonlinear regimes using the "standard" perturbative approach and a resummation technique, while we use the spherical dynamics to go beyond loworder results. This allows us to estimate the matter density power spectrum and bispectrum from linear to highly nonlinear scales, the full probability distribution of the density contrast on weakly nonlinear scales, and the halo mass function. We analyse the impact of modifications of gravity on these quantities for a few realistic models. In particular, we find that the standard oneloop perturbative approach is not sufficiently accurate to probe these effects on the power spectrum and it is necessary to use resummation methods even on weakly nonlinear scales which provide the best observational window for modified gravity as relative deviations from General Relativity do not grow significantly on smaller scales where theoretical predictions become increasingly difficult.Physical review D: Particles and fields 05/2012; 86(6).  [Show abstract] [Hide abstract]
ABSTRACT: Large ongoing and upcoming galaxy cluster surveys in the optical, Xray and millimetric wavelengths will provide rich samples of galaxy clusters at unprecedented depths. One key observable for constraining cosmological models is the correlation function of these objects, measured through their spectroscopic redshift. We study the redshiftspace correlation functions of clusters of galaxies, averaged over finite redshift intervals, and their covariance matrices. Expanding as usual the angular anisotropy of the redshiftspace correlation on Legendre polynomials, we consider the redshiftspace distortions of the monopole as well as the next two multipoles, $2\ell=2$ and 4. Taking into account the Kaiser effect, we developed an analytical formalism to obtain explicit expressions of all contributions to these mean correlations and covariance matrices. We include shotnoise and samplevariance effects as well as Gaussian and nonGaussian contributions. We obtain a reasonable agreement with numerical simulations for the mean correlations and covariance matrices on large scales ($r> 10 h^{1}$Mpc). Redshiftspace distortions amplify the monopole correlation by about $1020%$, depending on the halo mass, but the signaltonoise ratio remains of the same order as for the realspace correlation. This distortion will be significant for surveys such as DES, Erosita, and Euclid, which should also measure the quadrupole $2\ell=2$. The third multipole, $2\ell=4$, may only be marginally detected by Euclid.Astronomy and Astrophysics 05/2012; · 4.48 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the performance of an analytic model of the 3D matter distribution, which combines perturbation theory with halo models, for weaklensing configurationspace statistics. We compared our predictions for the weaklensing convergence twopoint and threepoint correlation functions with numerical simulations and fitting formulas proposed in previous works. We also considered the second and thirdorder moments of the smoothed convergence and of the aperturemass. As in our previous study of Fourierspace weaklensing statistics, we find that our model agrees better with simulations than previously published fitting formulas. Moreover, we recover the dependence on cosmology of these weaklensing statistics and we can describe multiscale moments. This approach allows us to obtain the quantitative relationship between these integrated weaklensing statistics and the various contributions to the underlying 3D density fluctuations, decomposed over perturbative, twohalo, or onehalo terms.Astronomy and Astrophysics 12/2011; · 4.48 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the performance of an analytic model of the 3D matter distribution, which combines perturbation theory with halo models, for weaklensing statistics. We compare our predictions for the weaklensing convergence power spectrum and bispectrum with numerical simulations and fitting formulas proposed in previous works. We find that this model provides better agreement with simulations than published fitting formulas. This shows that building on systematic and physically motivated models is a promising approach. Moreover, this makes explicit the link between the weaklensing statistics and the underlying properties of the 3D matter distribution, as a function of scale $\ell$. Thus, we obtain the contributions to the lensing power spectrum and bispectrum that arise from perturbative terms (complete up to oneloop) and nonperturbative terms (e.g., "1halo" term). Finally, we show that this approach recovers the dependence on cosmology (for realistic scenarios).Astronomy and Astrophysics 11/2011; · 4.48 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The Geometrical Adhesion Model (GAM) we described in previous papers provides a fully solved model for the nonlinear evolution of fields that mimic the cosmological evolution of pressureless fluids. In this context we explore the expected late time properties of the cosmic propagators once halos have formed, in a regime beyond the domain of application of perturbation theories. Whereas propagators in Eulerian coordinates are closely related to the velocity field we show here that propagators defined in Lagrangian coordinates are intimately related to the halo mass function. Exact results can be obtained in the 1D case. In higher dimensions, the computations are more intricate because of to the dependence of the propagators on the detailed shape of the underlying Lagrangianspace tessellations, that is, on the geometry of the regions that eventually collapse to form halos. We illustrate these results for both the 1D and the 2D dynamics. In particular we give here the expected asymptotic behaviors obtained for powerlaw initial power spectra. These analytical results are compared with the results obtained with dedicated numerical simulations.Physical review D: Particles and fields 09/2011;  [Show abstract] [Hide abstract]
ABSTRACT: We explore the cosmological constraints expected from wide area XMMtype cluster surveys covering 50–200 deg2, under realistic observing conditions. We perform a Fisher matrix analysis, based on cluster number counts in combination with estimates of the twopoint cluster correlation function. The effect of the survey design is implemented through an observationally welltested cluster selection function. Special attention is given to the modelling of the shot noise and sample variance, which we estimate by applying our selection function to numerically simulated surveys. We then infer the constraints on the equation of state of the dark energy, considering various survey configurations. We quantitatively investigate the respective impact of the cluster mass measurements, of the correlation function and of the 1 < z < 2 cluster population. We show that, with some 20 Ms XMM observing time, it is possible to constrain the dark energy parameters at a level comparable to that expected from the next generation of cosmic probes. Such a survey also has the power to provide unique insights into the physics of highredshift clusters and the properties of active galactic nuclei.Monthly Notices of the Royal Astronomical Society 06/2011; 414(2):1732  1746. · 5.52 Impact Factor
Publication Stats
664  Citations  
285.53  Total Impact Points  
Top Journals
Institutions

2011–2013

French National Centre for Scientific Research
 Institut d'astrophysique spatiale (IAS)
Lutetia Parisorum, ÎledeFrance, France


2010–2013

Cea Leti
Grenoble, RhôneAlpes, France


2006

University of Cambridge
Cambridge, England, United Kingdom


1999

CSU Mentor
Long Beach, California, United States
