Luciano Casarini

High-accuracy power spectra including baryonic physics in dynamical Dark Energy models

The next generation mass probes will obtain information on non-linear power spectra P(k, z) and their evolution, allowing us to investigate the nature of Dark Energy. To exploit such data we need high-precision simulations, extending at least up to scales of k ≃ 10h Mpc -1 , where the effects of baryons can no longer be neglected. In this paper, we present a series of large scale hydrodynamical simulations for ACDM and dynamical Dark Energy (dDE) models, in which the equation of state parameter is z dependent. The simulations include gas cooling, star formation and Supernovae feedback. They closely approximate the observed star formation rate and the observationally derived star/Dark Matter mass ratio in collapsed systems. Baryon dynamics cause spectral shifts exceeding 1 per cent at k > 2-3 h Mpc -1 compared to pure N-body simulations in the ACDM simulations. This agrees with previous studies, although we find a smaller effect (~50 per cent) on the power spectrum amplitude at higher k values. dDE exhibits similar behaviour, even though the dDE simulations produce ~20 per cent less stars than the analogous ACDM cosmologies. Finally, we show that the technique introduced in Casarini et al. to obtain spectra for any w(z) cosmology from constant-w models at any redshift still holds when gas physics is taken into account. While this relieves the need to explore the entire functional space of DE state equations, we illustrate a severe risk that future data analysis could lead to misinterpretation of the DE state equation.

Neutron Stars in Rastall Gravity

We calculate static and spherically symmetric solutions for the Rastall modification of gravity to describe Neutron Stars (NS). The key feature of the Rastall gravity is the non-conservation of the energy-momentum tensor proportionally to the space-time curvature. Using realistic equations of state for the NS interior we place a bound on the non-GR behaviour of the Rastall theory which should be

Tomographic weak-lensing shear spectra from large N-body and hydrodynamical simulations

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Dynamical dark energy simulations: high accuracy power spectra at high redshift

level. This work presents the more stringent contraints on the deviations of GR caused by the Rastall proposal.

Dark MaGICC: the effect of dark energy on disc galaxy formation. Cosmology does matter

Context. Forthcoming experiments will enable us to determine tomographic shear spectra at a high precision level. Most predictions about them have until now been based on algorithms yielding the expected linear and non-linear spectrum of density fluctuations. Even when simulations have been used, so-called Halofit predictions on fairly large scales have been needed. Aims. We wish to go beyond this limitation. Methods. We perform N-body and hydrodynamical simulations within a sufficiently large cosmological volume to allow a direct connection between simulations and linear spectra. While covering large length-scales, the simulation resolution is good enough to allow us to explore the high-� harmonics of the cosmic shear (up to � ∼ 50 000), well into the domain where baryon physics becomes important. We then compare shear spectra in the absence and in presence of various kinds of baryon physics, such as radiative cooling, star formation, and supernova feedback in the form of galactic winds. Results. We distinguish several typical properties of matter fluctuation spectra in the different simulations and test their impact on shear spectra. Conclusions. We compare our outputs with those obtainable using approximate expressions for non-linear spectra, and identify substantial discrepancies even between our results and those of purely N-body results. Our simulations and the treatment of their outputs however enable us, for the first time, to obtain shear results that are fully independent of any approximate expression, also in the high-� range, where we need to incorporate a non-linear power spectrum of density perturbations and the effects of baryon physics. This will allow us to fully exploit the cosmological information contained in future high-sensitivity cosmic shear surveys, exploring the physics of cosmic shears via weak lensing measurements.

Bouncing solutions in Rastall’s theory with a barotropic fluid

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.

Effects of coupled dark energy on the Milky Way and its satellites

We present the Dark MaGICC project, which aims to investigate the effect of Dark Energy (DE) modeling on galaxy formation via hydrodynamical cosmological simulations. Dark MaGICC includes four dynamical Dark Energy scenarios with time varying equations of state, one with a self-interacting Ratra-Peebles model. In each scenario we simulate three galaxies with high resolution using smoothed particle hydrodynamics (SPH). The baryonic physics model is the same used in the Making Galaxies in a Cosmological Context (MaGICC) project, and we varied only the background cosmology. We find that the Dark Energy parameterization has a surprisingly important impact on galaxy evolution and on structural properties of galaxies at z=0, in striking contrast with predictions from pure Nbody simulations. The different background evolutions can (depending on the behavior of the DE equation of state) either enhance or quench star formation with respect to a LCDM model, at a level similar to the variation of the stellar feedback parameterization, with strong effects on the final galaxy rotation curves. While overall stellar feedback is still the driving force in shaping galaxies, we show that the effect of the Dark Energy parameterization plays a larger role than previously thought, especially at lower redshifts. For this reason, the influence of Dark Energy parametrization on galaxy formation must be taken into account, especially in the era of precision cosmology.

Linear and non-linear perturbations in dark energy models

Rastall’s theory is a modification of Einstein’s theory of gravity where the covariant divergence of the stress-energy tensor is no more vanishing, but is proportional to the gradient of the Ricci scalar. The motivation of this theory is to investigate a possible non-minimal coupling of matter fields to geometry which, being proportional to the curvature scalar, may represent an effective description of quantum gravity effects. Non-conservation of the stress-energy tensor, via Bianchi identities, implies new field equations which have been recently used in a cosmological context, leading to some results of interest. In this paper we adopt Rastall’s theory to reproduce some features of the effective Friedmann equation emerging from loop quantum cosmology. We determine a class of bouncing cosmological solutions and comment about the possibility of employing these models as effective descriptions of a full quantum theory.

Dark matter velocity dispersion effects on CMB and matter power spectra

We present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and sub-galactic scales. We choose two constant couplings and a time-varying coupling function and we run simulations of three Milky-Way-size halos (

Physics of the Cosmic Microwave Background Radiation

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