Constraining the time variation of the coupling constants from cosmic microwave background: effect of \Lambda_{QCD}

We investigate constraints on the time variation of the fine structure constant between the recombination epoch and the present epoch, \Delta\alpha/\alpha \equiv (\alpha_{rec} - \alpha_{now})/\alpha_{now}, from cosmic microwave background (CMB) taking into account simultaneous variation of other physical constants, namely the electron mass m_{e} and the proton mass m_{p}. In other words, we consider the variation of Yukawa coupling and the QCD scale \Lambda_{QCD} in addition to the electromagnetic coupling. We clarify which parameters can be determined from CMB temperature anisotropy in terms of singular value decomposition. Assuming a relation among variations of coupling constants governed by a single scalar field (the dilaton), the 95% confidence level (C.L.) constraint on \Delta\alpha/\alpha is found to be -8.28 \times 10^{-3} < \Delta\alpha/\alpha < 1.81 \times 10^{-3}, which is tighter than the one obtained by considering only the change of \alpha and m_{e}. We also obtain the constraint on the time variation of the proton-to-electron mass ratio \mu \equiv m_{p}/m_{e} to be -0.52 < \Delta\mu/\mu < 0.17 (95% C.L.) under the same assumption. Finally, we also implement a forecast for constraints from the PLANCK survey.Comment: 25 pages, 4 figures; references adde

Dynamical Dark Energy model parameters with or without massive neutrinos

We use WMAP5 and other cosmological data to constrain model parameters in quintessence cosmologies, focusing also on their shift when we allow for non-vanishing neutrino masses. The Ratra-Peebles (RP) and SUGRA potentials are used here, as examples of slowly or fastly varying state parameter w(a). Both potentials depend on an energy scale \Lambda. Here we confirm the results of previous analysis with WMAP3 data on the upper limits on \Lambda, which turn out to be rather small (down to ~10^{-9} in RP cosmologies and ~10^{-5} for SUGRA). Our constraints on \Lambda are not heavily affected by the inclusion of neutrino mass as a free parameter. On the contrary, when the neutrino mass degree of freedom is opened, significant shifts in the best-fit values of other parameters occur.Comment: 9 pages, 3 figures, submitted to JCA

Investigating dark energy experiments with principal components

We use a principal component approach to contrast different kinds of probes of dark energy, and to emphasize how an array of probes can work together to constrain an arbitrary equation of state history w(z). We pay particular attention to the role of the priors in assessing the information content of experiments and propose using an explicit prior on the degree of smoothness of w(z) that is independent of the binning scheme. We also show how a figure of merit based on the mean squared error probes the number of new modes constrained by a data set, and use it to examine how informative various experiments will be in constraining the evolution of dark energy.Comment: A significantly expanded version with an added PCA for weak lensing, a new detailed discussion of the correlation prior proposed in this work, and a new discussion outlining the differences between the Bayesian and the frequentist approaches to reconstructing w(z). Matches the version accepted to JCAP. 8 pages, 2 figure

Early Dark Energy at High Redshifts: Status and Perspectives

Early dark energy models, for which the contribution to the dark energy density at high redshifts is not negligible, influence the growth of cosmic structures and could leave observable signatures that are different from the standard cosmological constant cold dark matter ($\Lambda$CDM) model. In this paper, we present updated constraints on early dark energy using geometrical and dynamical probes. From WMAP five-year data, baryon acoustic oscillations and type Ia supernovae luminosity distances, we obtain an upper limit of the dark energy density at the last scattering surface (lss), $\Omega_{\rm EDE}(z_{\rm lss})<2.3\times10^{-2}$ (95% C.L.). When we include higher redshift observational probes, such as measurements of the linear growth factors, Gamma-Ray Bursts (GRBs) and Lyman-$\alpha$ forest (\lya), this limit improves significantly and becomes $\Omega_{\rm EDE}(z_{\rm lss})<1.4\times10^{-3}$ (95% C.L.). Furthermore, we find that future measurements, based on the Alcock-Paczy\'nski test using the 21cm neutral hydrogen line, on GRBs and on the \lya forest, could constrain the behavior of the dark energy component and distinguish at a high confidence level between early dark energy models and pure $\Lambda$CDM. In this case, the constraints on the amount of early dark energy at the last scattering surface improve by a factor ten, when compared to present constraints. We also discuss the impact on the parameter $\gamma$, the growth rate index, which describes the growth of structures in standard and in modified gravity models.Comment: 11 pages, 9 figures and 4 table

The Cosmology of Asymmetric Brane Modified Gravity

We consider the asymmetric branes model of modified gravity, which can produce late time acceleration of the universe and compare the cosmology of this model to the standard $\Lambda$CDM model and to the DGP braneworld model. We show how the asymmetric cosmology at relevant physical scales can be regarded as a one-parameter extension of the DGP model, and investigate the effect of this additional parameter on the expansion history of the universe.Comment: 21 pages, 9 figures, journal versio

Reconstruction of the Primordial Power Spectrum by Direct Inversion

We introduce a new method for reconstructing the primordial power spectrum, $P(k)$, directly from observations of the Cosmic Microwave Background (CMB). We employ Singular Value Decomposition (SVD) to invert the radiation perturbation transfer function. The degeneracy of the multipole $\ell$ to wavenumber $k$ linear mapping is thus reduced. This enables the inversion to be carried out at each point along a Monte Carlo Markov Chain (MCMC) exploration of the combined $P(k)$ and cosmological parameter space. We present best--fit $P(k)$ obtained with this method along with other cosmological parameters.Comment: 23 pages, 9 figure

Constraints on neutrino masses from WMAP5 and BBN in the lepton asymmetric universe

In this paper, we put constraints on neutrino properties such as mass $m_{\nu}$ and degeneracy parameters $\xi_i$ from WMAP5 data and light element abundances by using a Markov chain Monte Carlo (MCMC) approach. In order to take consistently into account the effects of the degeneracy parameters, we run the Big Bang Nucleosynthesis code for each value of $\xi_i$ and the other cosmological parameters to estimate the Helium abundance, which is then used to calculate CMB anisotropy spectra instead of treating it as a free parameter. We find that the constraint on $m_{\nu}$ is fairly robust and does not vary very much even if the lepton asymmetry is allowed, and is given by $\sum m_\nu < 1.3 \rm eV$ ($95$).Comment: 19 pages, 7 figures, 5 table

The High Redshift Integrated Sachs-Wolfe Effect

In this paper we rely on the quasar (QSO) catalog of the Sloan Digital Sky Survey Data Release Six (SDSS DR6) of about one million photometrically selected QSOs to compute the Integrated Sachs-Wolfe (ISW) effect at high redshift, aiming at constraining the behavior of the expansion rate and thus the behaviour of dark energy at those epochs. This unique sample significantly extends previous catalogs to higher redshifts while retaining high efficiency in the selection algorithm. We compute the auto-correlation function (ACF) of QSO number density from which we extract the bias and the stellar contamination. We then calculate the cross-correlation function (CCF) between QSO number density and Cosmic Microwave Background (CMB) temperature fluctuations in different subsamples: at high z>1.5 and low z<1.5 redshifts and for two different choices of QSO in a conservative and in a more speculative analysis. We find an overall evidence for a cross-correlation different from zero at the 2.7\sigma level, while this evidence drops to 1.5\sigma at z>1.5. We focus on the capabilities of the ISW to constrain the behaviour of the dark energy component at high redshift both in the \LambdaCDM and Early Dark Energy cosmologies, when the dark energy is substantially unconstrained by observations. At present, the inclusion of the ISW data results in a poor improvement compared to the obtained constraints from other cosmological datasets. We study the capabilities of future high-redshift QSO survey and find that the ISW signal can improve the constraints on the most important cosmological parameters derived from Planck CMB data, including the high redshift dark energy abundance, by a factor \sim 1.5.Comment: 20 pages, 18 figures, and 7 table

Robust Neutrino Constraints by Combining Low Redshift Observations with the CMB

We illustrate how recently improved low-redshift cosmological measurements can tighten constraints on neutrino properties. In particular we examine the impact of the assumed cosmological model on the constraints. We first consider the new HST H0 = 74.2 +/- 3.6 measurement by Riess et al. (2009) and the sigma8*(Omegam/0.25)^0.41 = 0.832 +/- 0.033 constraint from Rozo et al. (2009) derived from the SDSS maxBCG Cluster Catalog. In a Lambda CDM model and when combined with WMAP5 constraints, these low-redshift measurements constrain sum mnu<0.4 eV at the 95% confidence level. This bound does not relax when allowing for the running of the spectral index or for primordial tensor perturbations. When adding also Supernovae and BAO constraints, we obtain a 95% upper limit of sum mnu<0.3 eV. We test the sensitivity of the neutrino mass constraint to the assumed expansion history by both allowing a dark energy equation of state parameter w to vary, and by studying a model with coupling between dark energy and dark matter, which allows for variation in w, Omegak, and dark coupling strength xi. When combining CMB, H0, and the SDSS LRG halo power spectrum from Reid et al. 2009, we find that in this very general model, sum mnu < 0.51 eV with 95% confidence. If we allow the number of relativistic species Nrel to vary in a Lambda CDM model with sum mnu = 0, we find Nrel = 3.76^{+0.63}_{-0.68} (^{+1.38}_{-1.21}) for the 68% and 95% confidence intervals. We also report prior-independent constraints, which are in excellent agreement with the Bayesian constraints.Comment: 19 pages, 6 figures, submitted to JCAP; v2: accepted version. Added section on profile likelihood for Nrel, improved plot

Dark Coupling and Gauge Invariance

We study a coupled dark energy-dark matter model in which the energy-momentum exchange is proportional to the Hubble expansion rate. The inclusion of its perturbation is required by gauge invariance. We derive the linear perturbation equations for the gauge invariant energy density contrast and velocity of the coupled fluids, and we determine the initial conditions. The latter turn out to be adiabatic for dark energy, when assuming adiabatic initial conditions for all the standard fluids. We perform a full Monte Carlo Markov Chain likelihood analysis of the model, using WMAP 7-year data.Comment: 16 pages, 2 figures, version accepted for publication in JCA