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We study the properties of dark matter (DM) halos in several models in which we have included dark energy (DE). We consider both dynamical DE, due to a scalar field self-interacting through Ratra-Peebles or supergravity potentials, and DE with constant negative w ¼ p= > À1. We find that at zero redshift, both the nonlinear power spectrum of DM and the mass function of halos do not depend appreciably on the state equation of DE, which implies that both statistics are almost indistinguishable from those of Ã-dominated cold dark matter (ÃCDM). This result is consistent with the nonlinear treatment in the accompanying paper and is also a welcome feature, because ÃCDM fits a large variety of data. On the other hand, DE halos differ from ÃCDM halos in that they are denser in their central parts, because DE halos collapsed earlier. Nevertheless, such differences are not so large. For example, the density at 10 kpc of a $10 13 M DE halo is only 50% denser than the ÃCDM halo. This means that DE does not ease the problem with cuspy DM profiles. Addressing another cosmological problem, the abundance of subhalos, we find that the number of satellites of halos in various DE models does not change with respect to ÃCDM when normalized to the same circular velocity as the parent halo. Most of the above similarities are related to choosing for all models the same normalization factor 8 at z ¼ 0. At high redshifts, different DE and ÃCDM models have different amplitudes of fluctuations, which causes substantial deviations of halo properties to occur. Therefore, the way to find which DE equation of state gives the best fit to the observed universe is to look at the evolution of halo properties. For example, the abundance of galaxy groups with mass larger than 10 13 h À1 M at ze2 can be used to discriminate between the models and thus to constrain the nature of DE.

Cosmological models with different types of Dark Energy are becoming viable alternatives for standard models with the cosmological constant. Yet, such models are more difficult to analyze and to simulate. We present analytical approximations and discuss ways of making simulations for two families of models, which cover a wide range of possibilities and include models with both slow and fast changing ratio w=p\rho. More specifically, we give analytical expressions for the evolution of the matter density parameter Omega_m(z) and the virial density contrast Delta_c at any redshift z. The latter is used to identify halos and to find their virial masses. We also provide an approximation for the linear growth factor of linear fluctuations between redshift z=40 and z=0. This is needed to set the normalization of the spectrum of fluctuations. Finally, we discuss the expected behavior of the halo mass function and its time evolution.Comment: 10 pages, 10 figures ApJ submitte

Within the frame of cosmologies where Dark Energy (DE) is a self-interacting scalar field, we allow for a CDM-DE coupling and non-zero neutrino masses, simultaneously. In their 0-0 version, i.e. in the absence of coupling and neutrino mass, these cosmologies provide an excellent fit to WMAP, SNIa and deep galaxy sample spectra, at least as good as ΛCDM. When the new degrees of freedom are open, we find that CDM-DE coupling and significant neutrino masses (∼ 0.1 eV per ν species) are at least as likely as the 0-0 option and, in some cases, even statistically favoured. Results are obtained by using a Monte Carlo Markov Chain approach.

We evaluate the mass function of virialized halos, by using Press & Schechter (PS) and/or Steth & Tormen (ST) expressions, for cosmologies where Dark Energy (DE) is due to a scalar selfinteracting field, coupled with Dark Matter (DM). We keep to coupled DE (cDE) models known to fit linear observables. To implement the PS-ST approach, we start from reviewing and extending the results of a previous work on the growth of a spherical top-hat fluctuation in cDE models, confirming their most intriguing astrophysical feature, i.e. a significant baryon-DM segregation, occurring well before the onset of any hydrodynamical effect. Accordingly, the predicted mass function depends on how halo masses are measured. For any option, however, the coupling causes a distortion of the mass function, still at z = 0. Furthermore, the z-dependence of cDE mass functions is mostly displaced, in respect to ΛCDM, in the opposite way of uncoupled dynamical DE. This is an aspect of the basic underlying result, that even a little DM-DE coupling induces relevant modifications in the non-linear evolution. Therefore, without causing great shifts in linear astrophysical observables, the DM-baryon segregation induced by the coupling can have an impact on a number of cosmological problems, e.g., galaxy satellite abundance, spiral disk formation, apparent baryon shortage, entropy input in clusters, etc..

Accurate predictions on non-linear power spectra, at various redshift z, will be a basic tool to interpret cosmological data from next generation mass probes, so obtaining key information on Dark Energy nature. This calls for high precision simulations, covering the whole functional space of w(z) state equations and taking also into account the admitted ranges of other cosmological parameters; surely a difficult task. A procedure was however suggested, able to match the spectra at z = 0, up to k ∼ 3 hMpc −1 , in cosmologies with an (almost) arbitrary w(z), by making recourse to the results of N -body simulations with w = const. In this paper we extend such procedure to high redshift and test our approach through a series of N -body gravitational simulations of various models, including a model closely fitting WMAP5 and complementary data. Our approach detects w = const. models, whose spectra meet the requirement within 1 % at z = 0 and perform even better at higher redshift, where they are close to a permil precision. Available Halofit expressions, extended to (constant) w = −1 are unfortunately unsuitable to fit the spectra of the physical models considered here. Their extension to cover the desired range should be however feasible, and this will enable us to match spectra from any DE state equation.PACS numbers: 98.80.-k, 98.65.-r

We study the possibility of mixed dark matter obtained through the phase space distribution of a single particle. An example is offered in the context of SUSY models with a Peccei-Quinn symmetry. Axinos in the 100 keV range can naturally have both thermal and non-thermal components. The latter one arises from the lightest neutralino decays and derelativizes at z ∼ 10 4 .