arXiv subjects

L. A. Popa

Publications and source records attributed to L. A. Popa.

46 records · Page 3Linked to original sources

arXiv2006

WMAP 3-year polarization data: Implications for the reionization history

We show that the delay of structure formation can not fully account for the reduction of electron optical depth from WMAP1 to WMAP3 when the radiative transfer effects and feedback mechanisms are took into account in computing the reionization history of the Universe. We also show that a PopIII stellar cluster with a mass of 80Mo and a heavy Larson initial mass function has an ionizing efficiency high enough to account for WMAP3 results, while in the case of WMAP1, a higher stellar mass of 1000Mo was required.

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arXiv2005

History of stellar evolution at high redshifts: Implications for the CMB E-mode polarization

The epoch of the end of reionization and the Thomson optical depth to the cosmic microwave background depend on the power spectrum amplitude on small scales and on the ionizing photon emissivity per unit mass in collapsed halos. In this paper is investigated the role of the radiative feedback effects for the temporal evolution of the ionizing emissivity. It is shown that the observational constrains on hydrogen photo-ionization rate based on Ly-$α$, Ly-$β$ and Ly-$γ$ Gunn-Peterson troughs and an electron optical depth consistent with the latest CMB measurements requires an emissivity of $\sim$10 ionizing photons per baryon and Hubble time at $z=6$. Through E-mode CMB polarization power spectrum measurements, it is expected that Planck experiment will have the sensitivity to distinguish between different histories of stellar evolution.

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arXiv2005

Radiative effects by high-z UV radiation background: Implications for the future CMB polarization measurements

We investigate the role of the radiative effects for the temporal evolution of the reionization fraction by using cosmological Smooth Particle Hydrodynamics (SPH) simulations. We find that the increase of photo-ionization and photo-heating rates due to optical depth effects results in a significantly contribute to the heating of the IGM before and during the reionization. The main effect of the UV radiation spectrum on the temporal evolution of the ionization fraction is given by the value of the reionization redshift and the redshift interval, in which the reionization is completed. We evaluate the effects of the UV radiation background on the CMB angular power spectrum taking into account different temporal evolutions of the ionization fraction. We show that through E-mode CMB polarization power spectrum measurements, the Planck experiment will have the sensitivity to distinguish between different reionization histories even when they imply the same optical depth to electron scattering and degenerated temperature anisotropy power spectra.

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arXiv2004

Cosmological reionization after WMAP: perspectives from PLANCK and future CMB missions

The WMAP first year detection of a high redshift reionization through its imprints on CMB anisotropy T and TE mode angular power spectra calls for a better comprehension of the universe ionization and thermal history after the standard recombination. Different reionization mechanisms predict different signatures in the CMB, both in temperature and polarization anisotropies and in spectral distortions. The Planck capability to distinguish among different scenarios through its sensitivity to T, TE, and E mode angular power spectra is discussed. Perspectives open by future high sensitivity experiments on the CMB polarization anisotropy and spectrum are also presented.

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arXiv2003

Signature of HDM clustering at Planck angular scales

We present the CMB anisotropy induced by the non-linear perturbations in the massive neutrino density associated to the non-linear gravitational clustering. We show that the non-linear time varying potential induced by the gravitational clustering process generates metric perturbations that affect the time evolution of the density fluctuations in all the components of the expanding Universe, leaving imprints on the CMB anisotropy power spectrum at subdegree angular scales. For a neutrino fraction in agreement with that indicated by the astroparticle and nuclear physics experiments and a cosmological accreting mass comparable with the mass of known clusters, we find that CMB anisotropy measurements with {\sc Planck} angular resolution and sensitivity possibly combined to other precise cosmological observations will allow the detection of the dynamical, linear and non-linear effects of the neutrino gravitational clustering.

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arXiv2003

Non-linear evolution of the cosmological background density field as diagnostic of the cosmological reionization

We present constraints on the cosmological and reionization parameters based on the cumulative mass function of the Ly-alpha systems. We find that the analysis of the cumulative mass function of the Ly-alpha systems indicates a reionization redshift z_r=24.2\+-4 (68%CL) in agreement with the value found on the basis of the WMAP anisotropy measurements, setting constraints on the amplitude of the density contrast, sigma_8=0.91+-0.04 (68\CL), similar to those derived from the X-ray cluster temperature function. Our joint analysis of Ly-alpha cumulative mass function and WMAP anisotropy measurements shows that the possible current identification of a running of the slope, dn_s/dlnk \ne 0, at k_p=0.05Mpc^-1 (multipole l of about 700) is mainly an effect of the existing degeneracy in the amplitude-slope plane at this scale, the result being consistent with the absence of running, the other constraints based on WMAP data remaining substantially unchanged. Finally, we evaluate the progress on the determination the considered parameters achievable by using the final temperature anisotropy data from WMAP and from the forthcoming Planck satellite that will significantly improve the sensitivity and reliability of these results. This work has been done in the framework of the Planck LFI activities.

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arXiv2002

Testing the principle of equivalence with Planck surveyor

We consider the effect of the violation of the equivalence principle (VEP) by the massive neutrino component on the Cosmic Microwave Background angular power specrum. We show that in the presence of adiabatic and isocurvature primordial density perturbations the Planck surveyor can place limits on the maximal VEP by the massive neutrino component at the level of 10^ -5, valid in the general relativity, for the case in which the gravity is the single source of VEP. This work has been performed within the framework of the {\sc Planck}/LFI activities.

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arXiv2002

Dynamical effects of the neutrino gravitational clustering at Planck angular scales

We study the CMB anisotropy induced by the non-linear perturbations in the massive neutrino density associated to the non-linear gravitational clustering proceses. Our results show that for the neutrino fraction in agreement with that indicated by the astroparticle and nuclear physics experiments and a cosmological accreting mass comparable with the mass of known clusters, the angular resolution and the sensitivity of the CMB anisotropy measurements from the Planck surveyor will allow the detection of the dynamical effects of the neutrino gravitational clustering.

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arXiv2002

Cosmological Implications of Massive Neutrinos

The massive neutrinos gravitational infall and their inprints left on the CMB temperature and matter density fluctuations power spectra are analysed taking into account the massive neutrino properties: the mass degeneracy, the phase space mixing, the lepton asymmetry.

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arXiv2001

Cosmological parameter determination from Planck and SDSS data in LambdaCHDM cosmologies

We study the complementarity between the cosmological information obtainable with the Planck surveyour and the large scale structure (LSS) redshift surveys in LambdaCHDM cosmologies. We compute the initial full phase-space neutrino distribution function for LambdaCHDM models by using numerical simulations. As initial condition we adopt the HDM density fluctuation power spectrum normalized on the basis of the analysis of the local cluster X-ray temperature function and derive the initial neutrino phase-space distribution at each spatial wave number k by using the Zel'dovich approximation. These initial neutrino phase-space distributions are implemented in the CMBFAST code for the integration of the coupled linearized Einstein, Boltzmann and fluid equations in k-space. We find that the relative bias between the CMB temperature fluctuations and the underlying matter density fluctuation power spectrum in COBE/DMR normalization is given by the CDM component normalized accordingly to the abundance of rich clusters at the present time. We use the Fisher information matrix approximation to constrain a multi-dimensional parametrization of the LambdaCHDM model, by jointly considering CMB and large scale structure data according to the Planck and the SDSS experimental specifications and by taking into account redshift distortions and nonlinear effects on the matter power spectrum. We found that, although the CMB anisotropy and polarization measurements tend to dominate the constraints on most of the cosmological parameters, the additional small scale LSS data help to break the parameter degeneracies. This work has been done in the framework of the Planck LFI activities.

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