Local Lagrangian Approximations for the Evolution of the Density Distribution Function in Large-Scale Structure

We examine local Lagrangian approximations for the gravitational evolution of the density distribution function. In these approximations, the final density at a Lagrangian point q at a time t is taken to be a function only of t and of the initial density at the same Lagrangian point. A general expression is given for the evolved density distribution function for such approximations, and we show that the vertex generating function for a local Lagrangian mapping applied to an initially Gaussian density field bears a simple relation to the mapping itself. Using this result, we design a local Lagrangian mapping which reproduces nearly exactly the hierarchical amplitudes given by perturbation theory for gravitational evolution. When extended to smoothed density fields and applied to Gaussian initial conditions, this mapping produces a final density distribution function in excellent agreement with full numerical simulations of gravitational clustering. We also examine the application of these local Lagrangian approximations to non-Gaussian initial conditions.Comment: LaTeX, 22 pages, and 11 postscript figure

Thawing quintessence with a nearly flat potential

The thawing quintessence model with a nearly flat potential provides a natural mechanism to produce an equation of state parameter, w, close to -1 today. We examine the behavior of such models for the case in which the potential satisfies the slow roll conditions: [(1/V)(dV/dphi)]^2 << 1 and (1/V)(d^2 V/dphi^2) << 1, and we derive the analog of the slow-roll approximation for the case in which both matter and a scalar field contribute to the density. We show that in this limit, all such models converge to a unique relation between 1+w, Omega_phi, and the initial value of (1/V)(dV/dphi). We derive this relation, and use it to determine the corresponding expression for w(a), which depends only on the present-day values for w and Omega_phi. For a variety of potentials, our limiting expression for w(a) is typically accurate to within delta w < 0.005 for w<-0.9. For redshift z < 1, w(a) is well-fit by the Chevallier-Polarski-Linder parametrization, in which w(a) is a linear function of a.Comment: 8 pages, 5 figures, discussion added, references updated, typos corrected, to appear in Phys. Rev.

User's Guide for ERB 7 SEFDT. Volume 1: User's Guide. Volume 2: Quality Control Report, Year 1

The Nimbus-7 ERB SEFDT Data User's Guide is presented. The guide consists of four subsections which describe: (1) the scope of the data User's Guide; (2) the background on Nimbus-7 Spacecraft and the ERB experiment; (3) the SEFDT data product and processing scenario; and (4) other related products and documents

Phantom Dark Energy Models with a Nearly Flat Potential

We examine phantom dark energy models produced by a field with a negative kinetic term and a potential that satisfies the slow roll conditions: [(1/V)(dV/dphi)]^2 << 1 and (1/V)(d^2 V/dphi^2) << 1. Such models provide a natural mechanism to produce an equation of state parameter, w, slightly less than -1 at present. Using techniques previously applied to quintessence, we show that in this limit, all such phantom models converge to a single expression for w(a), which is a function only of the present-day values of Omega_phi and w. This expression is identical to the corresponding behavior of w(a) for quintessence models in the same limit. At redshifts z < 1, this limiting behavior is well fit by the linear parametrization, w=w_0 + w_a(1-a), with w_a \approx -1.5(1+w_0).Comment: 4 pages, 2 figures, discussion added, to appear in Phys. Rev.

Generalizing the generalized Chaplygin gas

The generalized Chaplygin gas is characterized by the equation of state p = - A/rho^alpha, with alpha > -1 and w > -1. We generalize this model to allow for the cases where alpha < -1 or w < -1. This generalization leads to three new versions of the generalized Chaplygin gas: an early phantom model in which w << -1 at early times and asymptotically approaches w = -1 at late times, a late phantom model with w \approx -1 at early times and w -> - \infty at late times, and a transient model with w \approx -1 at early times and w -> 0 at late times. We consider these three cases as models for dark energy alone and examine constraints from type Ia supernovae and from the subhorizon growth of density perturbations. The transient Chaplygin gas model provides a possible mechanism to allow for a currently accelerating universe without a future horizon, while some of the early phantom models produce w < -1 without either past or future singularities.Comment: 8 pages, 9 figures, references added, to appear in Phys. Rev.

A method for the estimation of p-mode parameters from averaged solar oscillation power spectra

A new fitting methodology is presented which is equally well suited for the estimation of low-, medium-, and high-degree mode parameters from $m$-averaged solar oscillation power spectra of widely differing spectral resolution. This method, which we call the "Windowed, MuLTiple-Peak, averaged spectrum", or WMLTP Method, constructs a theoretical profile by convolving the weighted sum of the profiles of the modes appearing in the fitting box with the power spectrum of the window function of the observing run using weights from a leakage matrix that takes into account both observational and physical effects, such as the distortion of modes by solar latitudinal differential rotation. We demonstrate that the WMLTP Method makes substantial improvements in the inferences of the properties of the solar oscillations in comparison with a previous method that employed a single profile to represent each spectral peak. We also present an inversion for the internal solar structure which is based upon 6,366 modes that we have computed using the WMLTP method on the 66-day long 2010 SOHO/MDI Dynamics Run. To improve both the numerical stability and reliability of the inversion we developed a new procedure for the identification and correction of outliers in a frequency data set. We present evidence for a pronounced departure of the sound speed in the outer half of the solar convection zone and in the subsurface shear layer from the radial sound speed profile contained in Model~S of Christensen-Dalsgaard and his collaborators that existed in the rising phase of Solar Cycle~24 during mid-2010

Comparison of the mean photospheric magnetic field and the interplanetary magnetic field

Polarity comparison of solar magnetic field and interplanetary magnetic fiel

Limits on MeV Dark Matter from the Effective Number of Neutrinos

Thermal dark matter that couples more strongly to electrons and photons than to neutrinos will heat the electron-photon plasma relative to the neutrino background if it becomes nonrelativistic after the neutrinos decouple from the thermal background. This results in a reduction in N_eff below the standard-model value, a result strongly disfavored by current CMB observations. Taking conservative lower bounds on N_eff and on the decoupling temperature of the neutrinos, we derive a bound on the dark matter particle mass of m_\chi > 3-9 MeV, depending on the spin and statistics of the particle. For p-wave annihilation, our limit on the dark matter particle mass is stronger than the limit derived from distortions to the CMB fluctuation spectrum produced by annihilations near the epoch of recombination.Comment: 5 pages, 1 figure, discussion added, references added and updated, labels added to figure, to appear in Phys. Rev.