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Register a new userDynamical Constraints on the Cosmological Parameters
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Ying-Qiu Gu
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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.
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We present the first constraints on pure-gravity sector Standard-Model Extension (SME) parameters using Lunar Laser Ranging (LLR). LLR measures the round trip travel time of light between the Earth and the Moon. With 34+ years of LLR data, we have constrained six independent linear combinations of SME parameters at the level of $10^{-6}$ to $10^{-11}$. There is no evidence for Lorentz violation in the LLR dataset.
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.
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 show that solitonic cosmological gravitational waves propagated through the Friedmann universe and generated by the inhomogeneities of the gravitational field near the Big Bang can be responsible for increase of cosmological distances.
We present constraints on violations of Lorentz Invariance based on Lunar Laser Ranging (LLR) data. LLR measures the Earth-Moon separation by timing the round-trip travel of light between the two bodies, and is currently accurate to a few centimeters (parts in $10^{11}$ of the total distance). By analyzing archival LLR data under the Standard-Model Extension (SME) framework, we derived six observational constraints on dimensionless SME parameters that describe potential Lorentz-violation. We found no evidence for Lorentz violation at the $10^{-6}$ to $10^{-11}$ level in these parameters.
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