CMB and Cosmological Parameters: Current Status and Prospects

The last years have been an exciting period for the field of the Cosmic Microwave Background (CMB) research. With recent CMB balloon-borne and ground-based experiments we are entering a new era of 'precision' cosmology that enables us to use the CMB anisotropy measurements to constrain the cosmological parameters and test new theoretical scenarios.Comment: 21 pages, 5 figures. Based on an invited review at the XIII Rencontres de Blois - Frontiers of the Universe, June 17-23,200

First cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant

The recent observations of gravitational-wave and electromagnetic emission produced by the merger of the binary neutron-star system GW170817 have opened the possibility of using standard sirens to constrain the value of the Hubble constant. While the reported bound of $H_0=70_{-8}^{+12}$ at $68 \%$ C.L. is significantly weaker than those recently derived by observations of Cepheid variables, it does not require any form of cosmic distance ladder and can be considered as complementary and, in principle, more conservative. Here we combine, for the first time, the new measurement with the Planck Cosmic Microwave Background observations in a $12$ parameters extended $\Lambda$CDM scenario, where the Hubble constant is weakly constrained from CMB data alone and bound to a low value $H_0=55^{+7}_{-20}$ km/s/Mpc at $68 \%$ C.L. We point out that the non-Gaussian shape of the GW170817 bound makes lower values of the Hubble constant in worst agreement with observations than what expected from a Gaussian form. The inclusion of the new GW170817 Hubble constant measurement therefore significantly reduces the allowed parameter space, improving the cosmological bounds on several parameters as the neutrino mass, curvature and the dark energy equation of state.Comment: 5 pages, 4 Figures, few typos correcte

Planck constraints on neutrino isocurvature density perturbations

The recent Cosmic Microwave Background data from the Planck satellite experiment, when combined with HST determinations of the Hubble constant, are compatible with a larger, non-standard, number of relativistic degrees of freedom at recombination, parametrized by the neutrino effective number $N_{eff}$. In the curvaton scenario, a larger value for $N_{eff}$ could arise from a non-zero neutrino chemical potential connected to residual neutrino isocurvature density (NID) perturbations after the decay of the curvaton field, parametrized by the amplitude $\alpha^{NID}$. Here we present new constraints on $N_{eff}$ and $\alpha^{NID}$ from an analysis of recent cosmological data. We found that the Planck+WP dataset does not show any indication for a neutrino isocurvature component, severly constraining its amplitude, and that current indications for a non-standard $N_{eff}$ are further relaxed.Comment: 5 pages, 3 figure

Is Cosmology Compatible with Blue Gravity Waves ?

A primordial gravitational wave background with positive(blue) spectral index is expected in several non-standard inflationary cosmologies where the stress-energy tensor violates the null energy condition. Here we show that a sizable amount of blue gravitational waves is compatible with current cosmological and astrophysical data. So far most of the works on parameter estimation from cosmic microwave background data have assumed a negative or negligible spectral index. The present limits on cosmological parameters, especially on the scalar spectral index, widen up considerably when one allows also for blue tilts of the tensor spectrum. Since the amplitude of the CMB B-mode polarization is larger in these models, future data from Planck are likely to provide crucial measurements.Comment: 5 Pages, 5 Figure

Primordial Nucleosynthesis, Cosmic Microwave Background and Neutrinos

We report the results of a recent likelihood analysis combining the primordial nucleosynthesis and the BOOMERanG and MAXIMA-1 data on cosmic microwave background radiation anisotropies. We discuss the possible implications for relic neutrino background of a high value for the baryonic matter content of the universe, larger than what is expected in a standard nucleosynthesis scenario.Comment: 3 pages, 1 figure, some typos corrected, one reference added, presented by G. Mangano at NOW 2000, Europhysics Neutrino Oscillation Workshop, Otranto 200

The ν\nu generation: present and future constraints on neutrino masses from cosmology and laboratory experiments

We perform a joint analysis of current data from cosmology and laboratory experiments to constrain the neutrino mass parameters in the framework of bayesian statistics, also accounting for uncertainties in nuclear modeling, relevant for neutrinoless double $\beta$ decay ($0\nu2\beta$) searches. We find that a combination of current oscillation, cosmological and $0\nu2\beta$ data constrains $m_{\beta\beta}~<~0.045\,\mathrm{eV}$ ($0.014 \, \mathrm{eV} < m_{\beta\beta} < 0.066 \,\mathrm{eV}$) at 95\% C.L. for normal (inverted) hierarchy. This result is in practice dominated by the cosmological and oscillation data, so it is not affected by uncertainties related to the interpretation of $0\nu2\beta$ data, like nuclear modeling, or the exact particle physics mechanism underlying the process. We then perform forecasts for forthcoming and next-generation experiments, and find that in the case of normal hierarchy, given a total mass of $0.1\,$ eV, and assuming a factor-of-two uncertainty in the modeling of the relevant nuclear matrix elements, it will be possible to measure the total mass itself, the effective Majorana mass and the effective electron mass with an accuracy (at 95\% C.L.) of $0.05$, $0.015$, $0.02\,\mathrm{eV}$ respectively, as well as to be sensitive to one of the Majorana phases. This assumes that neutrinos are Majorana particles and that the mass mechanism gives the dominant contribution to $0\nu2\beta$ decay. We argue that more precise nuclear modeling will be crucial to improve these sensitivities.Comment: v2: 6 pages, 3 figures, 1 table; added definition of parameter minimal value from oscillation measurements; corrected confidence interval, that in v1 were reported at 90% C.L. and misidentified as 95% C.L.; accepted for publicatio

Cosmic Microwave Background Anisotropies from Global Texture

We investigate the global texture model of structure formation in cosmogonies with non-zero cosmological constant for different values of the Hubble parameter. We find that the absence of significant acoustic peaks and little power on large scales are robust predictions of these models. However, from a careful comparison with experiments we conclude that at present we cannot safely reject the model on the grounds of published CMB anisotropy data. If bias is close to one on large scales, galaxy correlation data rules out the models. New, very stringent constraints come from peculiar velocities. Investigating the large-N limit, we argue that our main conclusions apply to all global O(N) models of structure formation.Comment: 20 page LaTeX file, 11 postscript figs. included, proceedings to the EC conference on 3K Cosmology in Rome, Oct. 9