arXiv subjects

L. P. L. Colombo

Publications and source records attributed to L. P. L. Colombo.

156 records · Page 9Linked to original sources

arXiv2009

Do WMAP5 data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?

We fit WMAP5 and related data by allowing for a CDM--DE coupling and non--zero neutrino masses, simultaneously. We find a significant correlation between these parameters, so that simultaneous higher coupling and ν--masses are allowed. Furthermore, models with a significant coupling and ν--mass are statistically favoured in respect to a cosmology with no coupling and negligible neutrino mass (our best fits are: C ~ 1/2m_p, m_ν~ 0.12eV per flavor). We use a standard Monte Carlo Markov Chain approach, by assuming DE to be a scalar field self--interacting through Ratra--Peebles or SUGRA potentials.

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arXiv2009

Do data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?

We allow simultaneously for a CDM--DE coupling and non--zero neutrino masses and find that significant coupling and neutrino mass are (slightly) statistically favoured in respect to a cosmology with no coupling and negligible neutrino mass (our best fits are: C~1/2m_p, m_ν~0.12eV each flavor). We assume DE to be a self--interacting scalar field and use a standard Monte Carlo Markov Chain approach.

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arXiv2009

Do WMAP data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?

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 \LambdaCDM. When the new degrees of freedom are open, we find that CDM--DE coupling and significant neutrino masses (~0.1eV per νspecies) 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.

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arXiv2008

Higher neutrino mass allowed if Cold Dark Matter and Dark Energy are coupled

Cosmological limits on neutrino masses are softened, by more than a factor 2, if Cold Dark Matter (CDM) and Dark Energy (DE) are coupled. In turn, a neutrino mass yielding $Ω_ν$ up to $\sim0.20$ allows coupling levels $β\simeq 0.15, $ or more, already easing the coincidence problem. The coupling, in fact, displaces both $P(k)$ and $C_l$ spectra in a fashion opposite to neutrino mass. Estimates are obtained through a Fisher--matrix technique.

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arXiv2008

Cosmological parameters after WMAP5: forecasts for Planck and future galaxy surveys

The Planck satellite is expected to improve the measurement of most cosmological parameters by several factors with respect to current WMAP results. The actual performance may depend upon various aspects of the data analysis. In this paper we analyse the impact of specifics of the data analysis on the actual final results. We also explore the synergies in combining Planck results with future galaxy surveys. We find that Planck will improve constraints on most cosmological parameters by a factor 3-4 and on the tensor-to-scalar ratio r by a factor 9. Also inflationary parameters, like r, n_s and n_run, are no longer degenerate. The tensor spectral index, however, is little constrained. A combination of the 70 to 143 GHz channels will contain ~90% of all possible information, with 143 GHz polarisation information carrying about half of the constraining power on r. Also, the error on r degrades by a factor 2 if no B modes are included in the analysis. High-l temperature information is essential for determination of n_s and Ω_b, while improving noise properties increase the l-range where Planck would be cosmic variance limited in polarisation, with a significant improvement on the determination of r, τand A_s. However, a sub-percent difference in the FWHM used in the data analysis with respect to the one in the map will result in a bias for several parameters. Finally, Planck will greatly help future missions like LSST and CIP reach their potentials by providing tight constraints on parameters like n_s and n_run. Considering Planck together with these probes will help in breaking degeneracies between Ω_K and Ω_Λor Ω_dm and f_ν, resulting in improvements of several factors in the error associated to these parameters.

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arXiv2008

Gravitational Lensing Constraints on Dynamical and Coupled Dark Energy

Upcoming Weak Lensing (WL) surveys can be used to constrain Dark Energy (DE) properties, namely if tomographic techniques are used to improve their sensitivity. In this work, we use a Fisher matrix technique to compare the power of CMB anisotropy and polarization data with tomographic WL data, in constraining DE parameters. Adding WL data to available CMB data improves the detection of all cosmological parameters, but the impact is really strong when DE--DM coupling is considered, as WL tomography can then succeed to reduce the errors on some parameters by factors >10.

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arXiv2006

The Dark Side and its Nature

Although the cosmic concordance cosmology is quite successful in fitting data, fine tuning and coincidence problems apparently weaken it. We review several possibilities to ease its problems, by considering various kinds of dynamical Dark Energy and possibly its coupling to Dark Matter, trying to set observational limits on Dark Energy state equation and coupling.

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arXiv2006

Constraints on Quintessence From Using Cosmological Data

Recent data, including the three--year WMAP data, the full 2dF galaxy power spectrum and the first--year data of the Supernova Legacy Survey, are used to constrain model parameters in quintessence cosmologies. In particular, we discuss the inverse power--law (RP) and SUGRA potentials and compare parameter constraints with those for LCDM. Both potentials fit current observations with a goodness of fit comparable or better than LCDM. The constraints on the energy scale Lambda_DE appearing in both potential expressions are however different. For RP, only energy scales around the cosmological constant limit are allowed, making the allowed models quite similar to LCDM. For SUGRA, Lambda_DE values approximately up to Electroweak energy scale are still allowed, while other parameter intervals are slightly but significantly displaced. In particular a value of the primeval spectral index n_s = 1 is still allowed at the 95% c.l., and this can have an impact on constraints on possible inflationary potentials.

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arXiv2004

Cosmic Microwave Background Polarization and reionization: constraining models with a double reionization

Neutral hydrogen around high-z QSO and an optical depth tau ~ 0.17 can be reconciled if reionization is more complex than a single transition at z ~ 6-8. Tracing its details could shed a new light on the first sources of radiation. Here we discuss how far such details can be inspected through planned experiments on CMB large-scale anisotropy and polarization, by simulating an actual data analysis. By considering a set of double reionization histories of Cen (2003) type, a relevant class of models not yet considered by previous works, we confirm that large angle experiments rival high resolution ones in reconstructing the reionization history. We also confirm that reionization histories, studied with the prior of a single and sharp reionization, yield a biased tau, showing that this bias is generic. We further find a monotonic trend in the bias for the models that we consider, and propose an explanation of the trend, as well as the overall bias. We also show that in long-lived experiments such a trend can be used to discriminate between single and double reionization patterns.

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arXiv2003

Polarization Measures And Nature Of Dark Energy

Polarization measures, on wide angular scales, together with anisotropy data, can fix DE parameters. Here we discuss the sensitivity needed to provide significant limits. Our analysis puts in evidence that a class of models predicts low correlation or anticorrelation between polarization and anisotropy at low l. This class includes open models and models with DE due to a Ratra--Peebles (RP) potential. Results on this point, given in a previous paper of ours, are updated and partially corrected. We outline that, with the sensitivity of experiments like SPOrt or WMAP, high values of Lambda (energy scale in the RP potential) can be excluded. With the sensitivity expected for PLANCK, the selection will extend to much lower Lambda's.

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arXiv2003

Nature of Dark Energy and Polarization Measurements

High sensitivity polarization measures, on wide angular scales, together with data on anisotropy, can be used to fix DE parameters. In this paper, first of all, we aim to determine the sensitivity needed to provide significant limits. Our analysis puts in evidence that there is a class of DE models that polarization measures can possibly exclude soon. This class includes models with DE due to a Ratra-Peebles (RP) potential. Using a likelihood analysis, we show that it is possible to distinguish RP models from LCDM and other dynamical DE models, already with the sensitivity of experiments like SPOrt or WMAP, thanks to their negative TE correlation at low-l, when the optical depth tau is sufficiently large. On the contrary, fixing the energy scale Lambda for RP potentials or distinguishing between LCDM and other DE potentials requires a much lower pixel noise, that no planned polarization experiment will achieve. While reviewing this paper after the referee report, the first-year WMAP data were released. WMAP finds large positive anisotropy-polarization correlations at low l; this apparently excludes DE models with RP potentials.

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arXiv2002

Cosmic opacity to CMB photons and polarization measurements

Anisotropy data analysis leaves a significant degeneracy between primeval spectral index (n_s) and cosmic opacity to CMB photons (τ). Low--l polarization measures, in principle, can remove it. We perform a likelihood analysis to see how cosmic variance possibly affects such a problem. We find that, for a sufficiently low noise level (σ_{pix}) and if τis not negligibly low, the degeneracy is greatly reduced, while the residual impact of cosmic variance on n_s and τdeterminations is under control. On the contrary, if σ_{pix} is too high, cosmic variance effects appear to be magnified. We apply general results to specific experiments and find that, if favorable conditions occur, it is possible that a 2--σdetection of a lower limit on τis provided by the SPOrt experiment. Furthermore, if the PLANCK experiment will measure polarization with the expected precision, the error on low--l harmonics is adequate to determine τ, without significant magnification of the cosmic variance. This however indicates that high sensitivity might be more important than high resolution in τdeterminations. We also outline that a determination of τis critical to perform detailed analyses on the nature of dark energy and/or on the presence of primeval gravitational waves.

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