Sabino Matarrese

BARYONIC ACOUSTIC OSCILLATIONS VIA THE RENORMALIZATION GROUP

Renormalization Group techniques, successfully employed in quantum field theory and statistical physics, are applied to study the dynamics of structure formation in the Universe. A semi-analytic approach to the computation of the nonlinear power-spectrum of dark matter density fluctuations is proposed. The method can be applied down to zero redshift and to length scales where perturbation theory fails. Our predictions accurately fit the results of numerical simulations in reproducing the acoustic oscillations features of the power spectrum, which will be accurately measured in future galaxy surveys and will provide a probe to distinguish among different dark energy models.

The Asiago-ESO/RASS QSO Survey. III. Clustering Analysis and Theoretical Interpretation*

This is the third paper in a series describing the Asiago-ESO/RASS QSO Survey (AERQS), a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright quasi-stellar objects (QSOs; B ≤ 15) at z ≤ 0.3. We present here the clustering analysis of the full spectroscopically identified database (392 active galactic nuclei [AGNs]). The clustering signal at 0.02 < z < 0.22 is detected at a 3–4 σ level, and its amplitude is measured to be r0 = 8.6 ± 2.0 h-1 Mpc (in a Λ cold dark matter [ΛCDM] model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a way similar to radio galaxies, extremely red objects (EROs), and early-type galaxies in general, although with a marginally smaller amplitude. The comparison with recent results from the Two Degree Field (2dF) QSO Redshift Survey (2QZ) shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models, deriving interesting constraints on the typical mass of the dark matter halos hosting QSOs, MDMH ~ 1012.7 h-1 M⊙ (1012.0–1013.5 h-1 M⊙ at 1 σ confidence level). Finally, we use the clustering data to infer the physical properties of local AGNs, obtaining MBH ~ 2 × 108 h-1 M⊙ (1 × 107–3 × 109 h-1 M⊙) for the mass of the active black holes, τAGN ~ 8 × 106 yr (2 × 106–5 × 107 yr) for their lifetime and η ~ 0.14 for their efficiency (always for a ΛCDM model).

Modelling the IGM and the Lyα forest at high redshift from the dark matter distribution

A variety of approximate schemes for modelling the low-density intergalactic medium (IGM) in the high-redshift Universe are compared with the results of a large high-resolution hydrodynamical simulation. These schemes use either an analytical description of the dark matter distribution and the IGM or numerical simulations of the dark matter (DM) distributions combined with different approximate relations between dark matter field and the gas distribution. Schemes based on a filtering of the dark matter distribution with a global Jeans scale result in a rather poor description of the gas distribution. An adaptive filtering which takes into account the density/temperature dependence of the Jeans scale is required. A reasonable description of the gas distribution can be achieved using a fit of the mean relation between the dark matter and gas densities in the hydrodynamical simulation to relate dark matter and gas distribution. In the hydrodynamical simulations deviations from this mean relation are correlated with gradients in the dark matter peculiar velocity field indicative of shocks in the gas component. A scheme which takes into account this correlation results in a further improved gas distribution. Such adaptive filtering schemes applied to dark matter simulations will be very well suited for studies of statistical properties of the Lyα forest which investigate the IGM and the underlying dark matter distribution and require a large dynamic range and/or an extensive parameter study.

Dark energy effects on the Lyman α forest

In quintessence models, the dark energy content of the universe is described by a slowly rolling scalar field, the pressure and energy density of which obey an equation of state of the form p = wp; w is in general a function of time such that w < -1/3, in order to drive the observed acceleration of the Universe today. The cosmological constant model (ACDM) corresponds to the limiting case w = -1. In this paper, we explore the prospects of using the Lyman a forest to constrain w, using semi-analytical techniques to model the intergalactic medium (IGM). A different value of w changes both the growth factor and the Hubble parameter as a function of time. The resulting change in the optical depth distribution affects the optical depth power spectrum, the number of regions of high transmission per unit redshift and the cross-correlation coefficient of spectra of quasar pairs. These can be detected in current data, provided we have independent estimates of the thermal state of the IGM, its ionization parameter and the baryon density.

Maximal amount of gravitational waves in the curvaton scenario

The curvaton scenario for the generation of the cosmological curvature perturbation on large scales represents an alternative to the standard slow-roll scenario of inflation in which the observed density perturbations are due to fluctuations of the inflaton field itself. Its basic assumption is that the initial curvature perturbation due to the inflaton field is negligible. This is attained by lowering the energy scale of inflation, thereby highly suppressing the amount of gravitational waves produced during inflation. We compute the power spectrum of the gravitational waves generated at second order in perturbation theory by the curvaton (isocurvature) perturbations between the end of inflation and the curvaton decay. An interesting property of this contribution to the tensor perturbations is that it is directly proportional to the amount of non-Gaussianity predicted within the curvaton scenario. We show that the spectrum of gravitational waves may be in the range of future gravitational wave detectors.

Cosmology: Searching for Deviations from the Standard Cosmological Model

Cosmology is experiencing an exciting phase, characterized by the enormous amount of data which are already available or will soon become available. This epoch, which has been dubbed the era of precision cosmology, clearly requires an adequate theoretical effort to provide predictions at high level of accuracy. At the same time, the quality of the data available allows one to face with totally new and challenging questions. In this chapter we will focus on three complementary issues: (i) observable predictions of inflation in the early universe; (ii) a short overview of some cosmological effects of modified gravity scenarios; (iii) neutrinos in cosmology and large-scale structures.