1,343 research outputs found
Structure formation beyond shell-crossing: nonperturbative expansions and late-time attractors
Structure formation in 1+1 dimensions is considered, with emphasis on the
effects of shell-crossing. The breakdown of the perturbative expansion beyond
shell-crossing is discussed, and it is shown, in a simple example, that the
perturbative series can be extended to a transseries including nonperturbative
terms. The latter converges to the exact result well beyond the range of
validity of perturbation theory. The crucial role of the divergences induced by
shell-crossing is discussed. They provide constraints on the structure of the
transseries and act as a bridge between the perturbative and the
nonperturbative sectors. Then, we show that the dynamics in the deep
multistreaming regime is governed by attractors. In the case of simple initial
conditions, these attractors coincide with the asymptotic configurations of the
adhesion model, but in general they may differ. These results are applied to a
cosmological setting, and an algorithm to build the attractor solution starting
from the Zel'dovich approximation is developed. Finally, this algorithm is
applied to the search of `haloes' and the results are compared with those
obtained from the exact dynamical equations.Comment: 30 page
Ward identities and consistency relations for the large scale structure with multiple species
We present fully nonlinear consistency relations for the squeezed bispectrum
of Large Scale Structure. These relations hold when the matter component of the
Universe is composed of one or more species, and generalize those obtained in
Peloso, Pietroni '13 and Kehagias, Riotto '13 in the single species case. The
multi-species relations apply to the standard dark matter + baryons scenario,
as well as to the case in which some of the fields are auxiliary quantities
describing a particular population, such as dark matter halos or a specific
galaxy class. If a large scale velocity bias exists between the different
populations new terms appear in the consistency relations with respect to the
single species case. As an illustration, we discuss two physical cases in which
such a velocity bias can exist: (1) a new long range scalar force in the dark
matter sector (resulting in a violation of the equivalence principle in the
dark matter-baryon system), and (2) the distribution of dark matter halos
relative to that of the underlying dark matter field.Comment: Published versio
Galilean invariant resummation schemes of cosmological perturbations
Many of the methods proposed so far to go beyond Standard Perturbation Theory
break invariance under time-dependent boosts (denoted here as extended Galilean
Invariance, or GI). This gives rise to spurious large scale effects which spoil
the small scale predictions of these approximation schemes. By using
consistency relations we derive fully non-perturbative constraints that GI
imposes on correlation functions. We then introduce a method to quantify the
amount of GI breaking of a given scheme, and to correct it by properly tailored
counterterms. Finally, we formulate resummation schemes which are manifestly
GI, discuss their general features, and implement them in the so called
Time-Flow, or TRG, equations.Comment: 21 pages, 5 figure
Galilean invariance and the consistency relation for the nonlinear squeezed bispectrum of large scale structure
We discuss the constraints imposed on the nonlinear evolution of the Large
Scale Structure (LSS) of the universe by galilean invariance, the symmetry
relevant on subhorizon scales. Using Ward identities associated to the
invariance, we derive fully nonlinear consistency relations between statistical
correlators of the density and velocity perturbations, such as the power
spectrum and the bispectrum. These relations are valid up to O (f_{NL}^2)
corrections. We then show that most of the semi-analytic methods proposed so
far to resum the perturbative expansion of the LSS dynamics fail to fulfill the
constraints imposed by galilean invariance, and are therefore susceptible to
non-physical infrared effects. Finally, we identify and discuss a
nonperturbative semi-analytical scheme which is manifestly galilean invariant
at any order of its expansion.Comment: 29 pages, 7 figure
Spherical collapse and halo mass function in the symmetron model
We study the gravitational clustering of spherically symmetric overdensities
and the statistics of the resulting dark matter halos in the "symmetron model",
in which a new long range force is mediated by a symmetric scalar field.
Depending on the initial radius of the overdensity, we identify two distinct
regimes: for small initial radii the symmetron mediated force affects the
spherical collapse at all redshifts; for initial radii larger than some
critical size this force vanishes before collapse because of the symmetron
screening mechanism. In both cases overdensities collapse earlier than in the
CDM and statistically tend to form more massive dark matter halos.
Regarding the halo-mass function of these objects, we observe order one
departures from standard CDM predictions. The formalism developed here
can be easily applied to other models where fifth-forces participate to the
dynamics of the gravitational collapse.Comment: 17 pages, 5 figures. Minor revisions to match published versio
Local transformations of units in Scalar-Tensor Cosmology
The physical equivalence of Einstein and Jordan frame in Scalar Tensor
theories has been explained by Dicke in 1962: they are related by a local
transformation of units. We discuss this point in a cosmological framework. Our
main result is the construction of a formalism in which all the physical
observables are frame-invariant. The application of this approach to CMB codes
is at present under analysis.Comment: To appear in the proceedings of IRGAC 2006, 2nd International
Conference on Quantum Theories and Renormalization Group in Gravity and
Cosmology, Barcelona, July 11-15 200
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