Generalizing a Unified Model of Dark Matter, Dark Energy, and Inflation with Non Canonical Kinetic Term

We study a unification model for dark energy, dark matter, and inflation with a single scalar field with non canonical kinetic term. In this model the kinetic term of the Lagrangian accounts for the dark matter and dark energy, and at early epochs a quadratic potential accounts for slow roll inflation. The present work is an extension to the work by Bose and Majumdar [1] with a more general kinetic term that was proposed by Chimento in [2]. We demonstrate that the model is viable at the background and linear perturbation levels.Comment: 8 pages, 2 figures. Minor changes to text and formulae, and added 3 references to match the published version in Phys. Rev.

Different homogeneity detectors for improving space-time adaptive radar performance in heterogeneous clutter

© Copyright 2006 IEEESecondary data selection for estimation of the clutter covariance matrix in space-time adaptive processing (STAP) is normally obtained from cells (range rings) in close proximity of the cell under test. The aim of this paper is the analysis of performance improvement of Space-Time Adaptive radars when secondary data selection is obtained by discriminating between quasi-homogeneous areas on the ground which generate clutter with different statistics (i.e. clutter edges including littoral, farmland-wooded hills or rural-urban interfaces). The algorithm presented in this paper, referred to as the Different Homogeneity Detector (DHD), has been tested with simulated data obtained by using a general clutter model and a uniform linear array.Massimo Bertacca, Douglas A. Gray, Luke Rosenber

Unified Dark Matter models with fast transition

We investigate the general properties of Unified Dark Matter (UDM) fluid models where the pressure and the energy density are linked by a barotropic equation of state (EoS) $p = p(\rho)$ and the perturbations are adiabatic. The EoS is assumed to admit a future attractor that acts as an effective cosmological constant, while asymptotically in the past the pressure is negligible. UDM models of the dark sector are appealing because they evade the so-called "coincidence problem" and "predict" what can be interpreted as $w_{\rm DE} \approx -1$, but in general suffer the effects of a non-negligible Jeans scale that wreak havoc in the evolution of perturbations, causing a large Integrated Sachs-Wolfe effect and/or changing structure formation at small scales. Typically, observational constraints are violated, unless the parameters of the UDM model are tuned to make it indistinguishable from $\Lambda$CDM. Here we show how this problem can be avoided, studying in detail the functional form of the Jeans scale in adiabatic UDM perturbations and introducing a class of models with a fast transition between an early Einstein-de Sitter CDM-like era and a later $\Lambda$CDM-like phase. If the transition is fast enough, these models may exhibit satisfactory structure formation and CMB fluctuations. To consider a concrete case, we introduce a toy UDM model and show that it can predict CMB and matter power spectra that are in agreement with observations for a wide range of parameter values.Comment: 30 pages, 15 figures, JHEP3 style, typos corrected; it matches the published versio

ISW effect in Unified Dark Matter Scalar Field Cosmologies: an analytical approach

We perform an analytical study of the Integrated Sachs-Wolfe (ISW) effect within the framework of Unified Dark Matter models based on a scalar field which aim at a unified description of dark energy and dark matter. Computing the temperature power spectrum of the Cosmic Microwave Background anisotropies we are able to isolate those contributions that can potentially lead to strong deviations from the usual ISW effect occurring in a $\Lambda$CDM universe. This helps to highlight the crucial role played by the sound speed in the Unified Dark Matter models. Our treatment is completely general in that all the results depend only on the speed of sound of the dark component and thus it can be applied to a variety of unified models, including those which are not described by a scalar field but relies on a single dark fluid.Comment: 15 pages, LateX file; one comment after Eq.(36) and formula (44) added in order to underline procedure and main results. Accepted for publication in JCAP; some typos correcte

Clustering of quintessence on horizon scales and its imprint on HI intensity mapping

Quintessence can cluster only on horizon scales. What is the effect on the observed matter distribution? To answer this, we need a relativistic approach that goes beyond the standard Newtonian calculation and deals properly with large scales. Such an approach has recently been developed for the case when dark energy is vacuum energy, which does not cluster at all. We extend this relativistic analysis to deal with dynamical dark energy. Using three quintessence potentials as examples, we compute the angular power spectrum for the case of an HI intensity map survey. Compared to the concordance model with the same small-scale power at z = 0, quintessence boosts the angular power by up to 15% at high redshifts, while power in the two models converges at low redshifts. The difference is mainly due to the background evolution, driven mostly by the normalization of the power spectrum today. The dark energy perturbations make only a small contribution on the largest scales, and a negligible contribution on smaller scales. Ironically, the dark energy perturbations remove the false boost of large-scale power that arises if we impose the (unphysical) assumption that the dark energy is smooth.Web of Scienc

An entirely analytical cosmological model

The purpose of the present study is to show that in a particular cosmological model, with an affine equation of state, one can obtain, besides the background given by the scale factor, Hubble and deceleration parameters, a representation in terms of scalar fields and, more important, explicit mathematical expressions for the density contrast and the power spectrum. Although the model so obtained is not realistic, it reproduces features observed in some previous numerical studies and, therefore, it may be useful in the testing of numerical codes and as a pedagogical tool.Comment: 4 pages (revtex4), 4 figure

Cosmic degeneracies III: N-body simulations of Interacting Dark Energy with non-Gaussian initial conditions

We perform for the first time N-body simulations of interacting dark energy assuming non-Gaussian initial conditions, with the aim of investigating possible degeneracies of these two theoretically independent phenomena in different observational probes. We focus on the large-scale matter distribution, as well as on the statistical and structural properties of collapsed haloes and cosmic voids. On very large scales, we show that it is possible to choose the interaction and non-Gaussian parameters such that their effects on the halo power spectrum cancel, and the power spectrum is indistinguishable from a \u39b cold dark matter (\u2060\u39bCDM) model. On small scales, measurements of the non-linear matter power spectrum, halo-matter bias, halo and subhalo mass function, and cosmic void number function validate the degeneracy determined on large scales. However, the internal structural properties of haloes and cosmic voids, namely halo concentration\u2013mass relation and void density profile, are very different from those measured in the \u39bCDM model, thereby breaking the degeneracy. In practice, the values of fNL required to cancel the effect of interaction are already ruled by observations. Our results show in principle that the combination of large- and small-scale probes is needed to constrain interacting dark energy and primordial non-Gaussianity separately

Affine equation of state from quintessence and k-essence fields

We explore the possibility that a scalar field with appropriate Lagrangian can mimic a perfect fluid with an affine barotropic equation of state. The latter can be thought of as a generic cosmological dark component evolving as an effective cosmological constant plus a generalized dark matter. As such, it can be used as a simple, phenomenological model for either dark energy or unified dark matter. Furthermore, it can approximate (up to first order in the energy density) any barotropic dark fluid with arbitrary equation of state. We find that two kinds of Lagrangian for the scalar field can reproduce the desired behaviour: a quintessence-like with a hyperbolic potential, or a purely kinetic k-essence one. We discuss the behaviour of these two classes of models from the point of view of the cosmological background, and we give some hints on their possible clustering properties.Comment: 9 pages, 6 figures. Minor updates, accepted by CQ

Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity

We extend previous analyses of wide-angle correlations in the galaxy power spectrum in redshift space to include all general relativistic effects. These general relativistic corrections to the standard approach become important on large scales and at high redshifts, and they lead to new terms in the wide-angle correlations. We show that in principle the new terms can produce corrections of nearly 10 % on Gpc scales over the usual Newtonian approximation. General relativistic corrections will be important for future large-volume surveys such as SKA and Euclid, although the problem of cosmic variance will present a challenge in observing this.Comment: 14 pages, 5 figures; Typo in equation 5 corrected; results unaffecte

Cosmological scalar fields that mimic the ΛCDM\Lambda CDM cosmological model

We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard $\Lambda CDM$ cosmological model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric distance and angular diameter distance as functions on $z$). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and separable scalar field Lagrangians (power-law kinetic term + power-law potential). Exact analytic solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some degeneracy leading to lower precision in determination of $\Omega_m$. To remove this degeneracy additional information is needed beyond the data on large-scale geometry.Comment: VIII International Conference "Relativistic Astrophysics, Gravitation and Cosmology": May 21-23, 2008, Kyiv, Ukrain