Window Function for Non-Circular Beam CMB Anisotropy Experiment

We develop computationally rapid methods to compute the window function for a cosmic microwave background anisotropy experiment with a non-circular beam which scans over large angles on the sky. To concretely illustrate these methods we compute the window function for the Python V experiment which scans over large angles on the sky with an elliptical Gaussian beam.Comment: 27 pages, 5 figure

Median Statistics, H_0, and the Accelerating Universe

(Abridged) We develop median statistics that provide powerful alternatives to chi-squared likelihood methods and require fewer assumptions about the data. Applying median statistics to Huchra's compilation of nearly all estimates of the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics assume only that the measurements are independent and free of systematic errors. This estimate is arguably the best summary of current knowledge because it uses all available data and, unlike other estimates, makes no assumption about the distribution of measurement errors. The 95% range of purely statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result leads us to analyze the range of possible systematic errors in the median, which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over the statistical errors. A Bayesian median statistics treatment of high-redshift Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess et al. yields a posterior probability that the cosmological constant Lambda > 0 of 70 or 89%, depending on the prior information used. The posterior probability of an open universe is about 47%. Analysis of the Perlmutter et al. high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al. odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe Ia data do not rule out a time-variable Lambda model, and may even favor it over a time-independent Lambda and a Lambda = 0 open model.Comment: Significant revisions include discussion of systematic errors in the median of H_0. Accepted for publication in The Astrophysical Journal, v548, February 20, 2001 issue. 47 pages incl. figures and table

HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON THE REDSHIFT OF THE DECELERATION-ACCELERATION TRANSITION, DYNAMICAL DARK ENERGY, AND SPACE CURVATURE

Citation: Farooq, O., Madiyar, F. R., Crandall, S., & Ratra, B. (2017). HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON THE REDSHIFT OF THE DECELERATION-ACCELERATION TRANSITION, DYNAMICAL DARK ENERGY, AND SPACE CURVATURE. Astrophysical Journal, 835(1), 11. doi:10.3847/1538-4357/835/1/26We compile an updated list of 38 measurements of the Hubble parameter H(z) between redshifts 0.07 <= z <= 2.36 and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration-acceleration transition, z(da), from these H(z) data. Within the error bars, the measured zda are insensitive to the model used, depending only on the value assumed for the Hubble constant H-0. The weighted mean of our measurements is z(da) = 0.72 +/- 0.05 (0.84 +/- 0.03) for H-0 = 68 +/- 2.8 (73.24 +/- 1.74) km s(-1) Mpc(-1) and should provide a reasonably model-independent estimate of this cosmological parameter. The H(z) data are consistent with the standard spatially flat.CDM cosmological model but do not rule out nonflat models or dynamical dark energy models

Supernovae Ia Constraints on a Time-Variable Cosmological "Constant"

The energy density of a scalar field $\phi$ with potential $V(\phi) \propto \phi^{-\alpha}$, $\alpha > 0$, behaves like a time-variable cosmological constant that could contribute significantly to the present energy density. Predictions of this spatially-flat model are compared to recent Type Ia supernovae apparent magnitude versus redshift data. A large region of model parameter space is consistent with current observations. (These constraints are based on the exact scalar field model equations of motion, not on the widely used time-independent equation of state fluid approximation equations of motion.) We examine the consequences of also incorporating constraints from recent measurements of the Hubble parameter and the age of the universe in the constant and time-variable cosmological constant models. We also study the effect of using a non-informative prior for the density parameter.Comment: Accepted for publication in Ap

Quintessence duality

We join quintessence cosmological scenarios with the duality simmetry existing in string dilaton cosmologies. Actually, we consider the tracker potential type $V = V_0/{\phi}^{\alpha}$ and show that duality is only established if $\alpha = - 2$.Comment: 6 LaTex Pages, submitted to Physics Letters A; completely revised version: majior changes in the last par

Diffusion of ions through some Indian timbers

A simple diffusion cell (which can be easily constructed from perspex sheeting) for studying the passage of molecules, ions, gases, vapours and liquids through wood and other membranes is described. The diffusion of ions through some species of Indian timbers under variety of conditions has been studied and the results reported. The results show that the diffusion of ions through wood obeys Fick's law as long as the ion does not react with any constituents of the wood. In other cases there is deviation from this law. The diffusion constant is largest in the axial direction and smallest in the tangential direction. As against other claims, for the species tested, ionic diffusion is higher through sapwood than through heartwood. Temperature increases the rate of diffusion of ions. Diffusion of copper sulphate through cellophane is in conformity with Fick's law and is of the same order as for some timbers

Cosmological Constraints from Compact Radio Source Angular Size versus Redshift Data

We use the Gurvits, Kellermann, & Frey compact radio source angular size versus redshift data to place constraints on cosmological model parameters in models with and without a constant or time-variable cosmological constant. The resulting constraints are consistent with but weaker than those determined using current supernova apparent magnitude versus redshift data.Comment: 7 pages, 3 figures,ApJ accepted, minor changes, references adde

Variational dynamics in open spacetimes

We study the effect of non-vanishing surface terms at spatial infinity on the dynamics of a scalar field in an open FLRW spacetime. Starting from the path-integral formulation of quantum field theory we argue that classical physics is described by field configurations which extremize the action functional in the space of field configurations for which the variation of the action is well defined. Since these field configurations are not required to vanish outside a bounded domain, there is generally a non-vanishing contribution of a surface term to the variation of the action. We then investigate whether this surface term has an effect on the dynamics of the action-extremizing field configurations. This question appears to be surprisingly nontrivial in the case of the open FLRW geometry, since surface terms tend to grow as fast as volume terms in the infinite volume limit. We find that surface terms can be important for the dynamics of the field at a classical and at a quantum level, when there are supercurvature perturbations.Comment: 21 pages, Latex, no figure

CMB Anisotropy in COBE-DMR-Normalized Flat Λ\Lambda CDM Cosmogony

We compute the cosmic microwave background (CMB) anisotropy in a low-density, flat, cosmological constant, cold dark matter model which is normalized to the two-year COBE DMR sky map. Although conclusions regarding model viability must remain tentative until systematic effects are better understood, there are mild indications that these models have more intermediate scale power than is indicated by presently available CMB anisotropy observational data, with old ($t_0 \geq 15-16$Gyr), high baryon density ($\Omega_B \geq 0.0175 h^{-2}$), low density ($\Omega_0 \sim 0.2-0.4$) models doing the worst.Comment: 9 pages including 2 figures, one 5 pages table: two uuencoded postscript file

A conjecture on the origin of dark energy

The physical origin of holographic dark energy (HDE) is investigated. The main existing explanations, namely the UV/IR connection argument of Cohen et al, Thomas' bulk holography argument, and Ng's spacetime foam argument, are shown to be not satisfactory. A new explanation of the HDE model is then proposed based on the ideas of Thomas and Ng. It is suggested that the dark energy might originate from the quantum fluctuations of spacetime limited by the event horizon of the universe. Several potential problems of the explanation are also discussed.Comment: 11 pages, no figure