Stefania Pandolfi

Constraints on massive sterile neutrino species from current and future cosmological data

Sterile massive neutrinos are a natural extension of the Standard Model of elementary particles. The energy density of the extra sterile massive states affects cosmological measurements in an analogous way to that of active neutrino species. We perform here an analysis of current cosmological data and derive bounds on the masses of the active and the sterile neutrino states as well as on the number of sterile states. The so-called (3+2) models with three sub-eV active massive neutrinos plus two sub-eV massive sterile species is well within the 95% CL allowed regions when considering cosmological data only. If the two extra sterile states have thermal abundances at decoupling, Big Bang Nucleosynthesis bounds compromise the viability of (3+2) models. Forecasts from future cosmological data on the active and sterile neutrino parameters are also presented. Independent measurements of the neutrino mass from tritium beta decay experiments and of the Hubble constant could shed light on sub-eV massive sterile neutrino scenarios.

No evidence for dark energy dynamics from a global analysis of cosmological data

We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, w(z). We constrain w(z) in multiple redshift bins, utilizing the most recent data from type Ia supernovae, the cosmic microwave background, baryon acoustic oscillations, the integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike other recent analyses, we find no significant evidence for evolving dark energy; the data remain completely consistent with a cosmological constant. We also study the extent to which the time evolution of the equation of state would be constrained by a combination of current- and future-generation surveys, such as Planck and the Joint Dark Energy Mission.

When did cosmic acceleration start

A precise determination, and comparison, of the epoch of the onset of cosmic acceleration, at redshift z{sub acc}, and of dark energy domination, at z{sub eq}, provides an interesting measure with which to parametrize dark energy models. By combining several cosmological data sets, we place constraints on the redshift and age of cosmological acceleration. For a {lambda}CDM model, we find the constraint z{sub acc}=0.76{+-}0.10 at 95% C.L., occurring 6.7{+-}0.4 Gyr ago. Allowing a constant equation of state but different from -1 changes the constraint to z{sub acc}=0.81{+-}0.12 (6.9{+-}0.5 Gyr ago), while dynamical models markedly increase the error on the constraint z{sub acc}=0.81{+-}0.30 (6.8{+-}1.4 Gyr ago). Unified dark energy models such as silent quartessence yield z{sub acc}=0.8{+-}0.16 (6.8{+-}0.6 Gyr ago). Interestingly, we find that the best fit z{sub acc} and z{sub eq} are remarkably insensitive to both the cosmological data sets and theoretical dark energy models considered.

Probing dark energy with redshift-drift

Universit´e Paul Sabatier—Toulouse III, 118 route de Narbonne 31062 Toulouse Cedex 9, France(Dated: January 8, 2014)Future redshift-drift measurements (also known as Sandage-Loeb signal) will be crucial to probethe so called “redshift desert”, thus providing a new tool for cosmological studies. In this paperwe quantify the ability of a future measurement of the Sandage-Loeb signal by a CODEX-likespectrograph to constrain a phenomenological parametrization of dynamical dark energy, specificallyby obtaining constraints on w

Impact of general reionization scenarios on extraction of inflationary parameters

We would like to thank William Kinney for useful discussion. O. M.s work is supported by the MICINN (Spain) Ramon y Cajal Contract Nos. AYA2008-03531 and CSD2007-00060. M. P. is supported by a MEC-FPU Spanish grant.

Dark Energy coupling with electromagnetism as seen from future low-medium redshift probes

Beyond the standard cosmological model where the late-time accelerated expansion of the universe is driven by a cosmological constant, the observed expansion can be reproduced as well by the introduction of an additional dynamical scalar field. In this case, the field is expected to be naturally coupled to the rest of the theorys fields, unless a (still unknown) symmetry suppresses this coupling. Therefore, this would possibly lead to some observational consequences, such as space-time variations of natures fundamental constants. In this paper we investigate the coupling between a dynamical Dark Energy model and the electromagnetic field, and the corresponding evolution of the fine structure constant (α) with respect to the standard local value α0.

Reionization of the Intergalactic Medium

After recombination the cosmic gas was left in a cold and neutral state. However, as the first stars and black holes formed within early galactic systems, their UV and X-ray radiation induced a gradual phase transition of the intergalactic gas into the warm and ionized state we currently observe. This process is known as cosmic reionization. Understanding how the energy deposition connected with galaxy and star formation shaped the properties of the intergalactic gas is one of the primary goals of present-day cosmology. In addition, reionization back reacts on galaxy evolution, determining many of the properties of the high-redshift galaxy population that represent the current frontier of our discovery of the cosmos. In these two Lectures we provide a pedagogical overview of cosmic reionization and intergalactic medium and of some of the open questions in these fields.