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We present the redshift-space generalization of the equal-time angular-averaged consistency relations between (l+n)- and n-point polyspectra (i.e., the Fourier counterparts of correlation functions) of the cosmological matter density field. Focusing on the case of the l=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 relation on the bispectrum in the squeezed limit (i.e., the limit where one wave number is much smaller than the other two) is valid to better than 20% up to 1??hMpc-1, for both the monopole and quadrupole at z=0.35, in a ΛCDM 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 1 hMpc-1, at z=0.35 for the monopole. On larger scales, k=0.2?hMpc-1, it still holds within the statistical accuracy of idealized simulations of volume ~8?h-3Gpc³ without shot-noise error. [ABSTRACT FROM AUTHOR]

We investigate the small-scale static configurations of K-mouflage models defined by a general function K(x) of the kinetic terms. The fifth force is screened by the nonlinear K-mouflage mechanism if K'(x) grows sufficiently fast for large negative x. In the general nonspherically symmetric case, the fifth force is not aligned with the Newtonian force. For spherically symmetric static matter density profiles, we show that the results depend on the potential function W-(y)=yK'(-y2/2); i.e., W-(y) must be monotonically increasing to +∞ for y⩾0 to guarantee the existence of a single solution throughout space for any matter density profile. Small radial perturbations around these static profiles propagate as travelling waves with a velocity greater than the speed of light. Starting from vanishing initial conditions for the scalar field and for a time-dependent matter density corresponding to the formation of an overdensity, 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 nonmonotonic, there is an infinite number of discontinuous static solutions. However, the Klein-Gordon equation is no longer a well-defined hyperbolic equation, which leads to complex characteristic speeds and exponential instabilities. Therefore, these discontinuous static solutions are not physical, and these 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. All healthy K-mouflage models should satisfy K'>0, and W±(y)=yK'(±y2/2) are monotonically increasing to +∞ when y⩾0. [ABSTRACT FROM AUTHOR]

We study structure formation in K-mouflage 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 affected by both 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 ~ 2. At the one loop level, we find that the nonlinearities 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 A-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 A-CDM on nonlinear scales where a halo model is utilized. We find that the discrepancy peaks around 1 h 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. [ABSTRACT FROM AUTHOR]

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 A-CDM counterpart can be of the order five percent for redshifts 1 ≲ z ≲ 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 analyze 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 ≲ 1. [ABSTRACT FROM AUTHOR]

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 (ℓ + n) density correlation, with ℓ 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 ℓ 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 design analytical models of gravitational clustering. [ABSTRACT FROM AUTHOR]

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 (ℓ + n)-density correlation factors in terms of the n-point correlation and ℓ linear power spectrum factors, in the limit where the ℓ soft wave numbers become linear and much smaller than the n other wave numbers. We describe how these relations extend to multifluid cases. In the standard cosmology, these consistency relations derive from the equivalence principle. A detection of their violation would indicate non-Gaussian initial conditions, non-negligible decaying modes, or a modification of gravity that does not converge to general relativity on large scales. [ABSTRACT FROM AUTHOR]

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 baryon acoustic oscillation 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) (this also applies to the power spectra measured in numerical simulations). The real-space correlation function provides a better separation between perturbative and nonperturbative effects, which are restricted to x≲10h-1Mpc at all redshifts. [ABSTRACT FROM AUTHOR]

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 ΛCDM 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 ≲ 0.15h Mpc-1 at the perturbative level while the latter leads to a reasonable, up to a few percent, agreement with numerical simulations for k ≲ 3h Mpc-1 for large-curvature f(R) models, and k ≲ 1h 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. [ABSTRACT FROM AUTHOR]

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 "ZePdovich-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 ≤ 1h-1 Mpc--1, and on small scales, better than 10% for k 1h-1 Mpc-l, at z ≤ 0.35, which improves over previous methods. [ABSTRACT FROM AUTHOR]

We investigate whether the late-time (at z =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 ~ 3 on scales smaller than 0.1h-1 Mpc, which correspond to Lyman-ɑ clouds. Finally, we note that numerical simulations should start at zi = 100 rather than zi = 50 to avoid underestimating gravitational clustering at low redshifts. [ABSTRACT FROM AUTHOR]

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 parametrization 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 low-order 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 analyze the impact of modifications of gravity on these quantities for a few realistic models. In particular, we find that the standard one-loop 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. [ABSTRACT FROM AUTHOR]

In dimension 2 and above, the Burgers dynamics, the so-called "adhesion model" in cosmology, can actually give rise to several dynamics in the inviscid limit. We investigate here the statistical properties of the density field when it is defined by a "geometrical model' associated with this Burgers velocity field and where the matter distribution is fully determined, at each time step, by geometrical constructions. Our investigations are based on a set of numerical experiments that make use of an improved algorithm, for which the geometrical constructions are efficient and robust. In this work we focus on Gaussian initial conditions with power-law power spectra of slope n in the range -3

We propose a new mechanism for the formation of dark matter clumps in the radiation era. We assume that a light scalar field is decoupled from matter and oscillates harmonically around its vacuum expectation value. We include self-interactions and consider the nonrelativistic regime. The scalar dynamics are described by a fluid approach where the fluid pressure depends on both quantum and self-interaction effects. When the squared speed of sound of the scalar fluid becomes negative, an instability arises and the fluctuations of the scalar energy-density field start growing. They eventually become nonlinear and clumps form. Subsequently, the clumps aggregate and reach a universal regime. Afterwards, they play the role of cold dark matter. We apply this mechanism first to a model with a negative quartic term stabilized by a positive self-interaction of order six, and then to axion monodromy, where a subdominant cosine potential corrects a mass term. In the first case, the squared speed of sound becomes negative when the quartic term dominates, leading to a tachyonic instability. For axion monodromy, the instability starts very slowly after the squared speed of sound first becomes negative and then oscillates around zero. Initially the density perturbations perform acoustic oscillations due to the quantum pressure. Eventually, they start growing exponentially due to a parametric resonance. The shape and the scaling laws of the clumps depend on their formation mechanism. When the tachyonic phase takes place, the core density of the clumps is uniquely determined by the energy density at the beginning of the instability. On the other hand, for axion monodromy, the core density scales with the soliton mass and radius. This difference comes from the crucial role that the quantum pressure plays in both the parametric resonance in the linear regime and in the nonlinear formation regime of static scalar solitons. In both scenarios, the scalar-field clumps span a wide range of scales and masses, running from the size of atoms to that of galactic molecular clouds, and from 10-3 gram to thousands of solar masses. Because of finite-size effects, both from the source and the lens, these dark matter clumps are far beyond the reach of microlensing observations. We find that the formation redshift of the scalar clumps can span a large range in the radiation era; the associated background temperature can vary from 10 eV to 105 GeV, and the scalar-field mass from 10-26 GeV to 10 GeV. [ABSTRACT FROM AUTHOR]

We study the predictions for the matter redshift-space power spectrum and correlation function of a Lagrangian-space Gaussian ansatz introduced in a previous work. This model is a natural extension of the Zeldovich approximation, where the displacement and velocity power spectra are determined by the equations of motion, instead of being set equal to the linear power spectrum. It does not contain any free parameter. As for the real-space statistics, we find that this Lagrangian-space approach is much more efficient for the correlation functions than for the power spectra. The damping of the baryon acoustic oscillations (BAO) oscillations is well recovered, but there is a large smooth drift from the simulations in the power spectra. The multipoles of the correlation functions are well recovered on BAO scales, with an accuracy of 2% for ξs0 down to 10h-1 Mpc, and of 3% for ξs2 down to 26h-1 Mpc, at z≥0.35. [ABSTRACT FROM AUTHOR]

We present a new approach to model the gravitational dynamics of large-scale structures. Instead of solving the equations of motion up to a finite perturbative order or building phenomenological models, we follow the evolution of the probability distribution of the displacement and velocity fields within an approximation subspace. Keeping the exact equations of motion with their full nonlinearity, this provides a nonperturbative scheme that goes beyond shell crossing. Focusing on the simplest case of a curl-free Gaussian Ansatz for the displacement and velocity fields, we find that truncations of the power spectra on nonlinear scales directly arise from the equations of motion. This leads to a truncated Zeldovich approximation for the density power spectrum, but with a truncation that is not set a priori and with different power spectra for the displacement and velocity fields. The positivity of their autopower spectra also follows from the equations of motion. Although the density power spectrum is only recovered up to a smooth drift on baryon acoustic oscillation (BAO) scales, the predicted density correlation function agrees with numerical simulations within 2% from BAO scales down to 7 h - 1 Mpc at z = 0.35, without any free parameter. Thus, this parameter-free extension of the Zeldovich approximation is not competitive with other schemes for the power spectrum, but it provides a good prediction for the correlation function. However, the improvement over the standard Zeldovich approximation remains rather modest. This means that including non-Gaussianities will be essential to significantly improve analytical predictions within this general framework. [ABSTRACT FROM AUTHOR]

We consider scalar dark-matter models where the theory has a shift symmetry only broken by the scalar mass term. We restrict ourselves to k-essence kinetic terms where the shift symmetric part of the Lagrangian is a function of the first derivatives of the scalar field only. When the scalar mass is much larger than the inverse of the astrophysical time and length scales of interest, these models provide a description of dark-matter equivalent to the one given by theories with only polynomial interactions, in the low-amplitude regime where the self-interactions are small contributions to the Lagrangian. In this regime and in the nonrelativistic limit, which apply on large galactic scales, scalar clouds form solitons with a finite core. This provides an adequate model for dark-matter halos with no singular behavior. Close to the center of galaxies, where a supermassive black hole (BH) resides, we analyze the scalar-field distribution and the fate of the dark-matter soliton when subject to the BH gravitational attraction. We show that the scalar-field profile around such a central BH can be described by new oscillatory solutions of a modified Klein-Gordon equation, which generalize the harmonic oscillations of free scalar dark matter in a flat environment and the Jacobi elliptic functions of the ϕ4 model. Moreover, we find that, depending on the form of the k-essence kinetic term, regular solutions can be constructed or not, which connect the relativistic ingoing wavelike profile of the scalar field at the BH horizon to the nearly static nonrelativistic soliton at large distance. These profiles have a constant flux and represent the slow infall of scalar matter into the BH. We show that this regular behavior is only possible for k-essence functions that satisfy the usual conditions for the absence of ghosts and gradient instabilities, together with a new restriction on the growth of the kinetic function K(X) for large argument. It turns out that the same conditions of stability guarantee that quantum corrections are tamed, provided that the mass of the scalar field is less than 10-3 eV and the strong coupling scale of the model Λ is much larger than the scalar mass. [ABSTRACT FROM AUTHOR]

In scalar-field dark matter scenarios, a scalar-field soliton could form at the center of galactic halos, around the supermassive black holes that sit at the center of galaxies. Focusing on the large scalar-mass limit, where the soliton is formed by the balance between self-gravity and a repulsive self-interaction, we study the infall of the scalar field onto the central Schwarzschild black hole. We derive the scalar-field profile, from the Schwarzschild radius to the large radii dominated by the scalar cloud. We show that the steady state solution selects the maximum allowed flux, with a critical profile that is similar to the transonic solution obtained for the hydrodynamic case. This finite flux, which scales as the inverse of the self-interaction coupling, is small enough to allow the dark matter soliton to survive for many Hubble times. [ABSTRACT FROM AUTHOR]

We consider models of scalar dark matter with a generic interaction potential and noncanonical kinetic terms of the K-essence type that are subleading with respect to the canonical term. We analyze the low-energy regime and derive, in the nonrelativistic limit, the effective equations of motions. In the fluid approximation they reduce to the conservation of matter and to the Euler equation for the velocity field. We focus on the case where the scalar field mass 10-21≪m≲10-4 eV is much larger than for fuzzy dark matter, so that the quantum pressure is negligible on cosmological and galactic scales, while the self-interaction potential and noncanonical kinetic terms generate a significant repulsive pressure. At the level of cosmological perturbations, this provides a dark-matter density-dependent speed of sound. At the nonlinear level, the hydrostatic equilibrium obtained by balancing the gravitational and scalar interactions imply that virialized structures have a solitonic core of finite size depending on the speed of sound of the dark matter fluid. For the most relevant potential in λ4ϕ4/4 or K-essence with a (∂ϕ)4 interaction, the size of such stable cores cannot exceed 60 kpc. Structures with a density contrast larger than 106 can be accommodated with a speed of sound cs≲10-6. We also consider the case of a cosine self-interaction, as an example of bounded nonpolynomial self-interaction. This gives similar results in low-mass and low-density halos whereas solitonic cores are shown to be absent in massive halos. [ABSTRACT FROM AUTHOR]

We propose a simple model that provides a dynamical cancellation mechanism of the vacuum energy density appearing either in the form of a bare cosmological constant, quantum fluctuations of matter fields, or the result of phase transitions. This "conformal compensator model" is based on a conformal coupling A(φ) between the Einstein and the Jordan frames. This couples a second scalar field λ to the trace of the matter energy-momentum tensor, including the bare cosmological constant, and serves as a dynamical Lagrange multiplier. As a result, the scalar λ relaxes to a value which cancels the contributions from the vacuum energy density to the Friedmann equation, and adjusts itself to changes of the vacuum energy density after matter phase transitions. This circumvents Weinberg's theorem through the time dependence of the background scalar field φ. The radiation era, where the vacuum energy is annulled, is recovered in a natural manner. It is also possible to recover the matter era, via a tracking of the matter energy density by the scalar field, as well as the inflationary and dark energy eras, which correspond to regimes where the cancellation mechanism becomes inefficient. This suggests that inflation, dark energy, and the annulation of the vacuum energy density could be related to the same mechanism. In this setting, the usual fine-tuning of the vacuum energy is avoided, although the onset of the dark energy era at the appropriate time is not explained. [ABSTRACT FROM AUTHOR]

We consider the gravitational Wilsonian effective action at low energy when all the particles of the standard model have decoupled. When the R² terms dominate, the theory is equivalent to a scalar-tensor theory with the universal coupling β=1/√6 to matter for which we present strong lower and upper bounds on the scalaron mass m obtained by using results from the Eöt-Wash experiment on the modification of the inverse-square law, the observations of the hot gas of galaxy clusters, and the Planck satellite data on the neutrino masses. In terms of the range of the scalar interaction mediated over a distance of order m-1, this leads to the small interval 4μm≲m-1≲68μm within reach of future experimental tests of deviations from Newton's gravitational inverse-square law. [ABSTRACT FROM AUTHOR]

We describe the effects of the cosmological background on the K-mouflage screening properties of an astrophysical structure. We show that the K-mouflage screening of the spatial gradients of the scalar field, i.e., the screening of the fifth force, happens inside a dynamically generated screening radius. This radius is smaller than the location where the quasistatic approximation, i.e., where the spatial gradients exceed the time derivative, holds. Even though this quasistatic radius is much smaller than the size of the matter overdensity, spatial gradients remain well described by the quasistatic approximation up to the horizon. However, cosmologically we find that the time derivatives can remain dominant at redshifts z≳2, when the cosmic web shows a faster growth. Despite the existence of K-mouflage screening, we confirm that the values of the scalar field itself are still dominated by the cosmological background, down to the center of the matter overdensity, and that for instance the time drift of Newton's constant due to the large-scale cosmological evolution highly constrains K-mouflage models. [ABSTRACT FROM AUTHOR]

We analyze the role, on large cosmological scales and laboratory experiments, of the leading curvature squared contributions to the low-energy effective action of gravity. We argue for a natural relationship c0λ2 ≃1 at low energy between the R2 coefficients c0 of the Ricci scalar squared term in this expansion and the dark energy scale Λ=(λMPl)4 in four-dimensional Planck mass units. We show how the compatibility between the acceleration of the expansion rate of the Universe, local tests of gravity and the quantum stability of the model all converge to select such a relationship up to a coefficient which should be determined experimentally. When embedding this low-energy theory of gravity into candidates for its ultraviolet completion, we find that the proposed relationship is guaranteed in string-inspired supergravity models with modulus stabilization and supersymmetry breaking leading to de Sitter compactifications. In this case, the scalar degree of freedom of R2 gravity is associated to a volume modulus. Once written in terms of a scalar-tensor theory, the effective theory corresponds to a massive scalar field coupled with the universal strength β=1/√6 to the matter stress-energy tensor. When the relationship c0λ2≃1is realized, we find that on astrophysical scales and in cosmology the scalar field is ultralocal and therefore no effect arises on such large scales. On the other hand, the scalar field mass is tightly constrained by the nonobservation of fifth forces in torsion pendulum experiments such as Eöt-Wash. It turns out that the observation of the dark energy scale in cosmology implies that the scalar field could be detectable by fifth-force experiments in the near future. [ABSTRACT FROM AUTHOR]

We describe scalar-bimetric theories where the dynamics of the Universe are governed by two separate metrics, each with an Einstein-Hilbert term. In this setting, the baryonic and dark matter components of the Universe couple to metrics which are constructed as functions of these two gravitational metrics. More precisely, the two metrics coupled to matter are obtained by a linear combination of their vierbeins, with scalar-dependent coefficients. The scalar field, contrary to dark-energy models, does not have a potential of which the role is to mimic a late-time cosmological constant. The late-time acceleration of the expansion of the Universe can be easily obtained at the background level in these models by appropriately choosing the coupling functions appearing in the decomposition of the vierbeins for the baryonic and dark matter metrics. We explicitly show how the concordance model can be retrieved with negligible scalar kinetic energy. This requires the scalar coupling functions to show variations of order unity during the accelerated expansion era. This leads in turn to deviations of order unity for the effective Newton constants and a fifth force that is of the same order as Newtonian gravity, with peculiar features. The baryonic and dark matter self-gravities are amplified although the gravitational force between baryons and dark matter is reduced and even becomes repulsive at low redshift. This slows down the growth of baryonic density perturbations on cosmological scales, while dark matter perturbations are enhanced. These scalar-bimetric theories have a perturbative cutoff scale of the order of 1 AU, which prevents a precise comparison with Solar System data. On the other hand, we can deduce strong requirements on putative UV completions by analyzing the stringent constraints in the Solar System. Hence, in our local environment, the upper bound on the time evolution of Newton's constant requires an efficient screening mechanism that both damps the fifth force on small scales and decouples the local value of Newton constant from its cosmological value. This cannot be achieved by a quasistatic chameleon mechanism and requires going beyond the quasistatic regime and probably using derivative screenings, such as Kmouflage or Vainshtein screening, on small scales. [ABSTRACT FROM AUTHOR]

We investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. These models can be seen as the low-energy description of invariant field theories under a global Abelian symmetry. The scalar field is then identified with the Goldstone mode of the broken symmetry. It turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. This leads to a complete screening of the fifth force in the Solar System and between compact objects, through the ultralocal screening mechanism. On the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. Interestingly, it can either amplify or damp Newtonian gravity, depending on the model parameters. We also study the background cosmology and the linear cosmological perturbations. The background cosmology is hardly different from its Λ-CDM counterpart while cosmological perturbations crucially depend on whether the coupling function is convex or concave. For concave functions, growth is hindered by the repulsiveness of the fifth force while it is enhanced in the convex case. In both cases, the departures from the Λ-CDM cosmology increase on smaller scales and peak for galactic structures. For concave functions, the formation of structure is largely altered below some characteristic mass, as smaller structures are delayed and would form later through fragmentation, as in some warm dark matter scenarios. For convex models, small structures form more easily than in the Λ-CDM scenario. This could lead to an over-abundance of small clumps. We use a thermodynamic analysis and show that although convex models have a phase transition between homogeneous and inhomogeneous phases, on cosmological scales the system does not enter the inhomogeneous phase. On the other hand, for galactic halos, the coexistence of small and large substructures in their outer regions could lead to observational signatures of these models. [ABSTRACT FROM AUTHOR]

We investigate how the consistency relations of large-scale structures are modified when the initial density field is not Gaussian. We consider both scenarios where the primordial density field can be written as a nonlinear functional of a Gaussian field and more general scenarios where the probability distribution of the primordial density field can be expanded around the Gaussian distribution, up to all orders over δL0. Working at linear order over the non-Gaussianity parameters f(n)NL or Sn, we find that the consistency relations for the matter density fields are modified as they include additional contributions that involve all-order mixed linear-nonlinear correlations ⟨∏δL∏δ⟩. We derive the conditions needed to recover the simple Gaussian form of the consistency relations. This corresponds to scenarios that become Gaussian in the squeezed limit. Our results also apply to biased tracers and velocity or momentum cross-correlations. [ABSTRACT FROM AUTHOR]

We consider K-mouflage models, which are K-essence theories coupled to matter. We analyze their quantum properties and in particular the quantum corrections to the classical Lagrangian. We setup the renormalization program for these models and show that, contrary to renormalizable field theories where renormalization by infinite counterterms can be performed in one step, K-mouflage theories involve a recursive construction whereby each set of counterterms introduces new divergent quantum contributions which in turn must be subtracted by new counterterms. This tower of counterterms can be in principle constructed step by step by recursion and allows one to calculate the finite renormalized action of the model. In particular, it can be checked that the classical action is not renormalized and that the finite corrections to the renormalized action contain only higher-derivative operators. We concentrate then on the regime where calculability is ensured, i.e., when the corrections to the classical action are negligible. We establish an operational criterion for classicality and show that this is satisfied in cosmological and astrophysical situations for (healthy) K-mouflage models which pass the solar system tests. These results rely on perturbation theory around a background and are only valid when the background configuration is quantum stable. We analyze the quantum stability of astrophysical and cosmological backgrounds and find that models that pass the solar system tests are quantum stable. We then consider the possible embedding of the K-mouflage models in an UV completion. We find that the healthy models which pass the solar system tests all violate the positivity constraint which would follow from the unitarity of the putative UV completion, implying that these healthy K-mouflage theories have no UV completion. We then analyze their behavior at high energy, and we find that the classicality criterion is satisfied in the vicinity of a high-energy collision, implying that the classical K-mouflage theory can be applied in this context. Moreover, the classical description becomes more accurate as the energy increases, in a way compatible with the classicalization concept. [ABSTRACT FROM AUTHOR]

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 baryon acoustic oscillation 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) (this also applies to the power spectra measured in numerical simulations). The real-space correlation function provides a better separation between perturbative and nonperturbative effects, which are restricted to x≲10h-1Mpc at all redshifts [ABSTRACT FROM AUTHOR]

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 ΛCDM 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 0.15h Mpc-1 at the perturbative level while the latter leads to a reasonable, up to a few percent, agreement with numerical simulations for k≲3h Mpc-1 for large-curvature f(R) models, and k≲1h 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. [ABSTRACT FROM AUTHOR]

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 A-CDM by a factor of order 1 for masses M ≳ 1014h-1Mϴ. 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. [ABSTRACT FROM AUTHOR]

We present a class of modified-gravity theories which we call ultralocal models. We add a scalar field, with negligible kinetic terms, to the Einstein-Hilbert action. We also introduce a conformal coupling to matter. This gives rise to a new screening mechanism which is not entirely due to the nonlinearity of the scalar-field potential or the coupling function but to the absence of the kinetic term. As a result this removes any fifth force between isolated objects in vacuum. It turns out that these models are similar to chameleon-type theories with a large mass when considered outside the Compton wavelength but differ on shorter scales. The predictions of these models only depend on a single free function, as the potential and the coupling function are degenerate, with an amplitude given by a parameter α≲10-6, whose magnitude springs from requiring a small modification of Newton's potential astrophysically and cosmologically. This singles out a redshift zα~α-1/3≳100 where the fifth force is the greatest. The cosmological background follows the Λ cold dark matter (ΛCDM) history within a 10-6 accuracy, while cosmological perturbations are significantly enhanced (or damped) on small scales, k≳2hMpc-1 at z=0. The spherical collapse and the halo mass function are modified in the same manner. We find that the modifications of gravity are greater for galactic or subgalactic structures. We also present a thermodynamic analysis of the nonlinear and inhomogeneous fifth-force regime where we find that the Universe is not made more inhomogeneous before zα when the fifth force dominates, and does not lead to the existence of clumped matter on extra small scales inside halos for large masses while this possibility exists for masses M≲1011M⊙ where the phenomenology of ultralocal models would be most different from ΛCDM. [ABSTRACT FROM AUTHOR]

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 β 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 ΛCDM, 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. [ABSTRACT FROM AUTHOR]

The clustering ratio η, a large-scale structure observable originally designed to constrain the shape of the power spectrum of matter density fluctuations, is shown to provide a sensitive 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 spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 and 10 catalogs. We find that general relativity (GR), complemented with a Friedmann-Robertson-Walker (FRW) cosmological model with parameters fixed by the Planck satellite, describes extremely well the clustering of galaxies up to z~0.6. On large cosmic scales, the absolute amplitude of deviations from GR, |fRo|, is constrained to be smaller than 4.6 × 10-5 at the 95% confidence level. This bound makes cosmological probes of gravity almost competitive with the sensitivity of Solar System tests, although still one 1 order of magnitude less effective than astrophysical tests. We also extrapolate our results to future large surveys like Euclid and show that the astrophysical bound will certainly remain out of reach for such a class of modified-gravity models that only differ from ACDM at low redshifts. [ABSTRACT FROM AUTHOR]

We present a comprehensive derivation of linear perturbation equations for different matter species, including photons, baryons, cold dark matter, scalar fields, and 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 cosmic microwave background, 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 behavior of the K-mouflage model. [ABSTRACT FROM AUTHOR]