Voids and overdensities of coupled Dark Energy

We investigate the clustering properties of dynamical Dark Energy even in association of a possible coupling between Dark Energy and Dark Matter. We find that within matter inhomogeneities, Dark Energy migth form voids as well as overdensity depending on how its background energy density evolves. Consequently and contrarily to what expected, Dark Energy fluctuations are found to be slightly suppressed if a coupling with Dark Matter is permitted. When considering density contrasts and scales typical of superclusters, voids and supervoids, perturbations amplitudes range from $|\delta_\phi|\sim {\cal O} (10^{-6})$ to $|\delta_\phi|\sim {\cal O} (10^{-4})$ indicating an almost homogeneous Dark Energy component.Comment: 21 pages, 12 figures, submitted to JCA

Dark Matter, Dark Energy and the solution of the strong CP problem

The strong CP problem was solved by Peccei & Quinn by introducing axions, a viable candidate for Dark Matter (DM). Here the PQ approach is modified so to yield also Dark Energy (DE). DM and DE arise, in fai proportions, from a single scalar field, without tuning any extra parameter. In the present epoch, they are weakly coupled. Fluctuations have a fair evolution. The model is also fitted to the WMAP1 release, using a Markov Chain Monte Carlo technique, and performs as well as $\Lambda$CDM, coupled or uncoupled DE. Best--fit cosmological parameters for different models are mostly within 2--$\sigma$ level. Here, the main peculiarity of the model is to favor high values of the Hubble parameter.Comment: Proceeding of the workshop dsu2006, "The Dark Side of th Universe", Madrid, June 20-24, 200

Coupled DM heating in SCDEW cosmologies

Strongly Coupled Dark Energy plus Warm dark matter (SCDEW) cosmologies admit the stationary presence of $\sim 1\, \%$ of coupled-DM and DE, since inflationary reheating. Coupled-DM fluctuations therefore grow up to non-linearity even in the early radiative expansion. Such early non-linear stages are modelized here through the evolution of a top-hat density enhancement, reaching an early virial balance when the coupled-DM density contrast is just 25-26 and DM density enhancement is $\sim 10\, \%$ of total density. During the time needed to settle in virial equilibium, the virial balance conditions however continue to modify, so that "virialized" lumps undergo a complete evaporation. Here we outline that DM particles processed by overdentities preserve a fraction of their virial momentum. Although fully non-relativistic, the resulting velocities (moderately) affect the fluctuation dynamics over greater scales, entering the horizon later on.Comment: 20 pages, 7 figures; updated to match the published versio

Fluctuations in strongly coupled cosmologies

In the early Universe, a dual component made of coupled CDM and a scalar field $\Phi$, if their coupling $\beta > \sqrt{3}/2$, owns an attractor solution, making them a stationary fraction of cosmic energy during the radiation dominated era. Along the attractor, both such components expand $\propto a^{-4}$ and have early density parameters $\Omega_{d} = 1/ (4\beta^2)$ and $\Omega_c= 2, \Omega_d$ (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding $\propto a^{-3}$, breaks such stationary expansion at $z \sim 3$--$5 \times 10^3$, cosmic components gradually acquire densities consistent with observations. This paper, first of all, considers the case that this component is warm. However, its main topic is the analysis of fluctuation evolution: out of horizon modes are then determined; their entry into horizon is numerically evaluated as well as the dependence of Meszaros effect on the coupling $\beta$; finally, we compute: (i) transfer function and linear spectral function; (ii) CMB $C_l$ spectra. Both are close to standard $\Lambda$CDM models; in particular, the former one can be so down to a scale smaller than Milky Way, in spite of its main DM component being made of particles of mass $<1$ keV. The previously coupled CDM component, whose present density parameter is $\cal O$$(10^{-3})$, exhibits wider fluctuations $\delta \rho/\rho$, but approximately $\beta$-independent $\delta \rho$ values. We discuss how lower scale features of these cosmologies might ease quite a few problems that $\Lambda$CDM does not easily solve.Comment: 25 pages, 7 figures, accepted for publication on JCAP; updated to match the published versio

ISW-LSS cross-correlation in coupled Dark Energy models with massive neutrinos

We provide an exhaustive analysis of the Integrated Sach-Wolfe effect (ISW) in the context of coupled Dark Energy cosmologies where a component of massive neutrinos is also present. We focus on the effects of both the coupling between Dark Matter and Dark Energy and of the neutrino mass on the cross-correlation between galaxy/quasar distributions and ISW effect. We provide a simple expression to appropriately rescale the galaxy bias when comparing different cosmologies. Theoretical predictions of the cross-correlation function are then compared with observational data. We find that, while it is not possible to distinguish among the models at low redshifts, discrepancies between coupled models and $\Lambda$CDM increase with $z$. In spite of this, current data alone seems not able to distinguish between coupled models and $\Lambda$CDM. However, we show that upcoming galaxy surveys will permit tomographic analysis which allow to better discriminate among the models. We discuss the effects on cross-correlation measurements of ignoring galaxy bias evolution, b(z), and magnification bias correction and provide fitting formulae for b(z) for the cosmologies considered. We compare three different tomographic schemes and investigate how the expected signal to noise ratio, snr, of the ISW-LSS cross-correlation changes when increasing the number of tomographic bins. The dependence of snr on the area of the survey and the survey shot noise is also discussed.Comment: 18 pages, 23 figures. Several major extensions. New sections and figures was added. ApJ in prin