[Show abstract][Hide abstract] ABSTRACT: We describe K-mouflage models of modified gravity using the effective field
theory of dark energy. We show how the Lagrangian density $K$ defining the
K-mouflage models appears in the effective field theory framework, at both the
exact fully nonlinear level and at the quadratic order of the effective action.
We find that K-mouflage scenarios only generate the operator $(\delta
g^{00}_{(u)})^n$ at each order $n$. We also reverse engineer K-mouflage models
by reconstructing the whole effective field theory, and the full cosmological
behaviour, from two functions of the Jordan-frame scale factor in a tomographic
manner. This parameterisation is directly related to the implementation of the
K-mouflage screening mechanism: screening occurs when $ K'$ is large in a dense
environment such as the deep matter and radiation eras. In this way, K-mouflage
can be easily implemented as a calculable subclass of models described by the
effective field theory of dark energy which could be probed by future surveys.
[Show abstract][Hide abstract] ABSTRACT: We study Modified Gravity (MG) theories by modelling the redshifted matter
power spectrum in a spherical Fourier-Bessel (sFB) basis. We use a fully
non-linear description of the real-space matter power-spectrum and include the
lowest-order redshift-space correction (Kaiser effect), taking into account
some additional non-linear contributions. Ignoring relativistic corrections,
which are not expected to play an important role for a shallow survey, we
analyse two different modified gravity scenarios, namely the generalised
Dilaton scalar-tensor theories and the $f({R})$ models in the large curvature
regime. We compute the 3D power spectrum ${\cal C}^s_{\ell}(k_1,k_2)$ for
various such MG theories with and without redshift space distortions, assuming
precise knowledge of background cosmological parameters. Using an all-sky
spectroscopic survey with Gaussian selection function $\varphi(r)\propto
\exp(-{r^2 / r^2_0})$, $r_0 = 150 \, h^{-1} \, {\textrm{Mpc}}$, and number
density of galaxies $\bar {\textrm{N}} =10^{-4}\;{\textrm{Mpc}}^{-3}$, we use a
$\chi^2$ analysis, and find that the lower-order $(\ell \leq 25)$ multipoles of
${\cal C}^s_\ell(k,k')$ (with radial modes restricted to $k < 0.2 \, h
\,{\textrm{Mpc}}^{-1}$) can constraint the parameter $f_{R_0}$ at a level of
$2\times 10^{-5} (3\times 10^{-5})$ with $3 \sigma$ confidence for $n=1(2)$.
Combining constraints from higher $\ell > 25$ modes can further reduce the
error bars and thus in principle make cosmological gravity constraints
competitive with solar system tests. However this will require an accurate
modelling of non-linear redshift space distortions. Using a tomographic
$\beta(a)$-$m(a)$ parameterization we also derive constraints on specific
parameters describing the Dilaton models of modified gravity.
[Show abstract][Hide abstract] ABSTRACT: We use the cosmic shear data from the Canada-France-Hawaii Telescope Lensing
Survey to place constraints on $f(R)$ and {\it Generalized Dilaton} models of
modified gravity. This is highly complimentary to other probes since the
constraints mainly come from the non-linear scales: maximal deviations with
respects to the General-Relativity + $\Lambda$CDM scenario occurs at $k\sim1 h
\mbox{Mpc}^{-1}$. At these scales, it becomes necessary to account for known
degeneracies with baryon feedback and massive neutrinos, hence we place
constraints jointly on these three physical effects. To achieve this, we
formulate these modified gravity theories within a common tomographic
parameterization, we compute their impact on the clustering properties relative
to a GR universe, and propagate the observed modifications into the weak
lensing $\xi_{\pm}$ quantity. Confronted against the cosmic shear data, we
reject the $f(R)$ $\{ |f_{R_0}|=10^{-4}, n=1\}$ model with more than 99.9%
confidence interval (CI) when assuming a $\Lambda$CDM dark matter only model.
In the presence of baryonic feedback processes and massive neutrinos with total
mass up to 0.2eV, the model is disfavoured with at least 94% CI in all
different combinations studied. Constraints on the $\{ |f_{R_0}|=10^{-4},
n=2\}$ model are weaker, but nevertheless disfavoured with at least 89% CI. We
identify several specific combinations of neutrino mass, baryon feedback and
$f(R)$ or Dilaton gravity models that are excluded by the current cosmic shear
data. Notably, universes with three massless neutrinos and no baryon feedback
are strongly disfavoured in all modified gravity scenarios studied. These
results indicate that competitive constraints may be achieved with future
cosmic shear data.
[Show abstract][Hide abstract] ABSTRACT: We investigate the effects of a K-mouflage modification of gravity on the
dynamics of clusters of galaxies. We extend the description of K-mouflage to
situations where the scalar field responsible for the modification of gravity
is coupled to a perfect fluid with pressure. We describe the coupled system at
both the background cosmology and cosmological perturbations levels, focusing
on cases where the pressure emanates from small-scale nonlinear physics. We
derive these properties in both the Einstein and Jordan frames, as these two
frames already differ by a few percents at the background level for K-mouflage
scenarios, and next compute cluster properties in the Jordan frame that is
better suited to these observations. Galaxy clusters are not screened by the
K-mouflage mechanism and therefore feel the modification of gravity in a
maximal way. This implies that the halo mass function deviates from
$\Lambda$-CDM by a factor of order one for masses $M\gtrsim 10^{14} \ h^{-1}
M_\odot$. We then consider the hydrostatic equilibrium of gases embedded in
galaxy clusters and the consequences of K-mouflage on the X-ray cluster
luminosity, the gas temperature and the Sunyaev-Zel'dovich effect. We find that
the cluster temperature function, and more generally number counts, are largely
affected by K-mouflage, mainly due to the increased cluster abundance in these
models. Other scaling relations such as the mass-temperature and the
temperature-luminosity relations are only modified at the percent level due to
the constraints on K-mouflage from local Solar System tests.
[Show abstract][Hide abstract] ABSTRACT: We show that Solar System tests can place very strong constraints on
K-mouflage models of gravity, which are coupled scalar field models with
nontrivial kinetic terms that screen the fifth force in regions of large
gravitational acceleration. In particular, the bounds on the anomalous
perihelion of the Moon imposes stringent restrictions on the K-mouflage
Lagrangian density, which can be met when the contributions of higher order
operators in the static regime are sufficiently small. The bound on the rate of
change of the gravitational strength in the Solar System constrains the
coupling strength $\beta$ to be smaller than $0.1$. These two bounds impose
tighter constraints than the results from the Cassini satellite and Big Bang
Nucleosynthesis. Despite the Solar System restrictions, we show that it is
possible to construct viable models with interesting cosmological predictions.
In particular, relative to $\Lambda$-CDM, such models predict percent level
deviations for the clustering of matter and the number density of dark matter
haloes. This makes these models predictive and testable by forthcoming
observational missions.
Physical Review D 04/2015; 91(12). DOI:10.1103/PhysRevD.91.123522 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the redshift-space generalization of the equal-time
angular-averaged consistency relations between $(\ell+n)$- and $n$-point
polyspectra of the cosmological matter density field. Focusing on the case of
$\ell=1$ large-scale mode and $n$ small-scale modes, we use an approximate
symmetry of the gravitational dynamics to derive explicit expressions that hold
beyond the perturbative regime, including both the large-scale Kaiser effect
and the small-scale fingers-of-god effects. We explicitly check these
relations, both perturbatively, for the lowest-order version that applies to
the bispectrum, and nonperturbatively, for all orders but for the
one-dimensional dynamics. Using a large ensemble of $N$-body simulations, we
find that our squeezed bispectrum relation is valid to better than $20\%$ up to
$1h$Mpc$^{-1}$, for both the monopole and quadrupole at $z=0.35$, in a
$\Lambda$CDM cosmology. Additional simulations done for the Einstein-de Sitter
background suggest that these discrepancies mainly come from the breakdown of
the approximate symmetry of the gravitational dynamics. For practical
applications, we introduce a simple ansatz to estimate the new derivative terms
in the relation using only observables. Although the relation holds worse after
using this ansatz, we can still recover it within $20\%$ up to $1h$Mpc$^{-1}$,
at $z=0.35$ for the monopole. On larger scales, $k = 0.2 h\mathrm{Mpc}^{-1}$,
it still holds within the statistical accuracy of idealized simulations of
volume $\sim8h^{-3}\mathrm{Gpc}^3$ without shot-noise error.
[Show abstract][Hide abstract] 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 K-mouflage model as an example to demonstrate the
numerical implementation of our linear perturbation equations. K-mouflage 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 K-mouflage 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 K-mouflage model.
Physical Review D 11/2014; 91(6). DOI:10.1103/PhysRevD.91.063528 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents 52 X-ray bright galaxy clusters selected within the 11 deg2 XMM-LSS survey. 51 of them have spectroscopic redshifts (0.05 < z < 1.06), one is identified at zphot = 1.9, and all together make the high-purity ‘Class 1’ (C1) cluster sample of the XMM-LSS, the highest density sample of X-ray-selected clusters with a monitored selection function. Their X-ray fluxes, averaged
gas temperatures (median TX = 2 keV), luminosities (median LX, 500 = 5 × 1043 erg s−1) and total mass estimates (median 5 × 1013 h−1 M⊙) are measured, adapting to the specific signal-to-noise regime of XMM-LSS observations. Particular care is taken in deriving the sample selection function by means of realistic simulations reproducing
the main characteristics of XMM observations. The redshift distribution of clusters shows a deficit of sources when compared to the cosmological expectations,
regardless of whether Wilkinson Microwave Anisotropy Probe-9 or Planck-2013 cosmic microwave background parameters are assumed. This lack of sources is particularly noticeable at 0.4 ≲ z ≲ 0.9. However, after quantifying uncertainties due to small number statistics and sample variance, we are not able to put
firm (i.e. >3σ) 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 LX-TX relation (with respect to a self-similar evolution) is a plausible explanation for the observed deficit. We confirm this
evolutionary trend by directly studying how C1 clusters populate the LX-TX-z space, properly accounting for selection biases. We also 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. We provide in a table the catalogue of 52 clusters together with their measured properties.
Monthly Notices of the Royal Astronomical Society 08/2014; 444(3). DOI:10.1093/mnras/stu1625 · 5.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the small-scale static configurations of K-mouflage models
defined by a general function $K(\chi)$ of the kinetic terms. The fifth force
is screened by the nonlinear K-mouflage mechanism if $K'(\chi)$ grows
sufficiently fast for large negative $\chi$. In the general non-spherically
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
high-density 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 non-monotonic, there are an infinite number of
discontinuous static solutions but these are not physical and those models are
not theoretically sound. Such K-mouflage 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 small-scale
nonlinear analysis of screening models.
Physical Review D 08/2014; 90(12). DOI:10.1103/PhysRevD.90.123521 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The clustering ratio $\eta$, a large-scale 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.
Physical Review D 06/2014; 91(10). DOI:10.1103/PhysRevD.91.103503 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study structure formation in K-mouflage cosmology whose main feature is
the absence of screening effect on quasi-linear 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
non-linearities of the K-mouflage 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 K-mouflage 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 non-linear
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). DOI:10.1103/PhysRevD.90.023508 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the cosmology of K-mouflage 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 K-mouflage when the nonlinear kinetic
terms give rise to ghosts, particle excitations with negative energy. In this
case, we find that the K-mouflage theories can only be considered as an
effective description of the Universe at low energy below $1$ keV. In the safe
ghost-free models, we find that the equation of state always diverges in the
past and changes significantly by a few percent since $z\lesssim 1$.
Physical Review D 03/2014; 90(2). DOI:10.1103/PhysRevD.90.023507 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We explicitly test the equal-time consistency relation between the
angular-averaged bispectrum and the power spectrum of the matter density field,
employing a large suite of cosmological $N$-body simulations. This is the
lowest-order 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 leading-order 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). DOI:10.1103/PhysRevD.90.023546 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aims: We estimate the amplitude of the source-lens clustering
bias and of the intrinsic-alignment bias of weak-lensing estimators of
the two-point and three-point convergence and cosmic-shear correlation
functions. Methods: We use a linear galaxy bias model for the
galaxy-density correlations, as well as a linear intrinsic-alignment
model. For the three-point and four-point density correlations, we use
analytical or semi-analytical models, based on a hierarchical ansatz or
a combination of one-loop perturbation theory with a halo model.
Results: For two-point statistics, we find that the source-lens
clustering bias is typically several orders of magnitude below the
weak-lensing signal, except when we correlate a very low-redshift galaxy
(z2 ≲ 0.05) with a higher redshift galaxy (z1
≳ 0.5), where it can reach 10% of the signal for the shear. For
three-point statistics, the source-lens clustering bias is typically on
the order of 10% of the signal, as soon as the three galaxy source
redshifts are not identical. The intrinsic-alignment bias is typically
about 10% of the signal for both two-point and three-point statistics.
Thus, both source-lens clustering bias and intrinsic-alignment bias must
be taken into account for three-point estimators aiming at a better than
10% accuracy.
Appendices are available in electronic form at http://www.aanda.org
Astronomy and Astrophysics 01/2014; 561:53-. DOI:10.1051/0004-6361/201322146 · 4.38 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 $\ell$ large-scale linear wave numbers that are
integrated over angles, and $n$ fixed small-scale nonlinear wave numbers, in
terms of the small-scale $n$-point density correlation and $\ell$ prefactors
that involve the linear power spectra at the large-scale wave numbers. These
relations, which do not vanish for equal-time statistics, go beyond the already
known kinematic consistency relations. They could be used to detect primordial
non-Gaussianities, modifications of gravity, limitations of galaxy biasing
schemes, or to help designing analytical models of gravitational clustering.
Physical Review D 11/2013; 89(12). DOI:10.1103/PhysRevD.89.123522 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe how the kinematic consistency relations satisfied by density
correlations of the large-scale 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 multi-fluid 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 non-Gaussian
initial conditions or a modification of gravity that does not converge
to General Relativity on large scales.
Physical Review D 11/2013; 89(8). DOI:10.1103/PhysRevD.89.083534 · 4.64 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 well-ordered convergence and a finite correlation
function that yields a percent accuracy at the BAO peak (as soon as one goes to
second order). Lagrangian-space expansions are somewhat more efficient, when
truncated at low orders, but may diverge at high orders. We find that whereas
the uncertainty on the halo-profile mass-concentration 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 real-space 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). DOI:10.1103/PhysRevD.88.083524 · 4.64 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 quasi-linear to the non-linear
regime, using semi-analytical methods. For such models, where the range of the
new scalar field is typically within the Mpc range and below in the
cosmological context, non-linear 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
N-body 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.
[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 high-order diagrams, as in
perturbative resummation schemes, we embed the standard perturbation theory
within a realistic nonlinear Lagrangian-space ansatz. We also point out that an
"adhesion-like" regularization of the shell-crossing regime is more realistic
than a "Zel'dovich-like" behavior, where particles freely escape to infinity.
This provides a "cosmic web" power spectrum with good small-scale 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.
[Show abstract][Hide abstract] ABSTRACT: We investigate whether the late-time (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 late-time
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.