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Register a new userGlobal Constraints On Key Cosmological Parameters
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Data from Type Ia supernovae, along with X-ray cluster estimates of the universal baryon fraction and Big Bang Nucleosynthesis (BBN) determinations of the baryon-to-photon ratio, are used to provide estimates of several global cosmological parameters at epochs near zero redshift. We show that our estimate of the present baryon density is in remarkably good agreement with that inferred from BBN at high redshift, provided the primordial abundance of deuterium is relatively low and the Universe is flat. We also compare these estimates to the baryon density at z = 1100 as inferred from the CMB angular power spectrum.
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In cosmology, the cosmic curvature $K$ and the cosmological constant $Lambda$ are two important parameters, and the values have strong influence on the behavior of the universe. In the context of normal cosmology, under the ordinary assumptions of positive mass-energy and initial negative pressure, we find the initial singularity of the universe is certainly absent and we have $K=1$. This means total spatial structure of the universe should be a 3-dimensional sphere $S^3$. For the cyclic cosmological model, we have $Lambdalesssim 10^{-24} {rm ly}^{-2}$. Obviously, such constraints would be helpful for the researches on the properties of dark matter and dark energy in cosmology.
We set new constraints on a seven-dimensional space of cosmological parameters within the class of inflationary adiabatic models. We use the angular power spectrum of the cosmic microwave background measured over a wide range of ell in the first flight of the MAXIMA balloon-borne experiment (MAXIMA-1) and the low ell results from COBE/DMR. We find constraints on the total energy density of the universe, Omega=1.0^{+0.15}_{-0.30}, the physical density of baryons, Omega_{b}h^2=0.03 +/- 0.01, the physical density of cold dark matter, Omega_{cdm}h^2=0.2^{+0.2}_{-0.1}$, and the spectral index of primordial scalar fluctuations, n_s=1.08+/-0.1, all at the 95% confidence level. By combining our results with measurements of high-redshift supernovae we constrain the value of the cosmological constant and the fractional amount of pressureless matter in the universe to 0.45<Omega_Lambda<0.75 and 0.25<Omega_{m}<0.50, at the 95% confidence level. Our results are consistent with a flat universe and the shape parameter deduced from large scale structure, and in marginal agreement with the baryon density from big bang nucleosynthesis.
We discuss constraints on cosmic reionisation and their implications on a cosmic SFR density $rho_mathrm{SFR}$ model; we study the influence of key-parameters such as the clumping factor of ionised hydrogen in the intergalactic medium (IGM) $C_{H_{II}}$ and the fraction of ionising photons escaping star-forming galaxies to reionise the IGM $f_mathrm{esc}$. Our analysis uses SFR history data coming from luminosity functions, assuming that star-forming galaxies were sufficient to lead the reionisation process at high redshift. We add two other sets of constraints: measurements of the IGM ionised fraction and the most recent result from Planck Satellite about the integrated Thomson optical depth of the Cosmic Microwave Background (CMB) $tau_mathrm{Planck}$. We also consider various possibilities for the evolution of these two parameters with redshift, and confront them with observational data cited above. We conclude that, if the model of a constant clumping factor is chosen, the fiducial value of $3$ often used in papers is consistent with observations; even if a redshift-dependent model is considered, the resulting optical depth is strongly correlated to $C_{H_{II}}$ mean value at $z>7$, an additional argument in favour of the use of a constant clumping factor. Besides, the escape fraction is related to too many astrophysical parameters to allow us to use a complete and fully satisfactory model. A constant value with redshift seems again to be the most likely expression: considering it as a fit parameter, we get from the maximum likelihood (ML) model $f_mathrm{esc}=0.24pm0.08$; with a redshift-dependent model, we find an almost constant evolution, slightly increasing with $z$, around $f_mathrm{esc}=0.23$. Last, our analysis shows that a reionisation beginning as early as $zgeq14$ and persisting until $zsim6$ is a likely storyline.
In this paper, I revisit the constraints obtained by several authors (Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of Omegam, n and sigma_8 in the light of recent theoretical developments: 1) new theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 2001, Del Popolo 2002b); 2) a more accurate mass-temperature relation, also determined for arbitrary Omega_m and Omega_Lambda (Del Popolo 2002a).
Upcoming galaxy surveys will allow us to probe the growth of the cosmic large-scale structure with improved sensitivity compared to current missions, and will also map larger areas of the sky. This means that in addition to the increased precision in observations, future surveys will also access the ultra-large scale regime, where commonly neglected effects such as lensing, redshift-space distortions and relativistic corrections become important for calculating correlation functions of galaxy positions. At the same time, several approximations usually made in these calculations, such as the Limber approximation, break down at those scales. The need to abandon these approximations and simplifying assumptions at large scales creates severe issues for parameter estimation methods. On the one hand, exact calculations of theoretical angular power spectra become computationally expensive, and the need to perform them thousands of times to reconstruct posterior probability distributions for cosmological parameters makes the approach unfeasible. On the other hand, neglecting relativistic effects and relying on approximations may significantly bias the estimates of cosmological parameters. In this work, we quantify this bias and investigate how an incomplete modeling of various effects on ultra-large scales could lead to false detections of new physics beyond the standard $Lambda$CDM model. Furthermore, we propose a simple debiasing method that allows us to recover true cosmologies without running the full parameter estimation pipeline with exact theoretical calculations. This method can therefore provide a fast way of obtaining accurate values of cosmological parameters and estimates of exact posterior probability distributions from ultra-large scale observations.
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