The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Atsushi Taruya - One of the best experts on this subject based on the ideXlab platform.
-
Full-sky formulae for weak lensing Power Spectra from total angular momentum method
Journal of Cosmology and Astroparticle Physics, 2013Co-Authors: Daisuke Yamauchi, Toshiya Namikawa, Atsushi TaruyaAbstract:We systematically derive full-sky formulae for the weak lensing Power Spectra generated by scalar, vector and tensor perturbations from the total angular momentum (TAM) method. Based on both the geodesic and geodesic deviation equations, we first give the gauge-invariant expressions for the deflection angle and Jacobi map as observables of the CMB lensing and cosmic shear experiments. We then apply the TAM method, originally developed in the theoretical studies of CMB, to a systematic derivation of the angular Power Spectra. The TAM representation, which characterizes the total angular dependence of the spatial modes projected along a line-of-sight, can carry all the information of the lensing modes generated by scalar, vector, and tensor metric perturbations. This greatly simplifies the calculation, and we present a complete set of the full-sky formulae for angular Power Spectra in both the E-/B-mode cosmic shear and gradient-/curl-mode lensing potential of deflection angle. Based on the formulae, we give illustrative examples of non-vanishing B-mode cosmic shear and curl-mode of deflection angle in the presence of the vector and tensor perturbations, and explicitly compute the Power Spectra.
-
A Closure Theory for Nonlinear Evolution of Cosmological Power Spectra
The Astrophysical Journal, 2008Co-Authors: Atsushi Taruya, Takashi HiramatsuAbstract:We apply a nonlinear statistical method in turbulence to the cosmological perturbation theory and derive a closed set of evolution equations for matter Power Spectra. The resultant closure equations consistently recover the one-loop results of standard perturbation theory, and beyond that, it is still capable of treating the nonlinear evolution of matter Power Spectra. We find the exact integral expressions for the solutions of closure equations. These analytic expressions coincide with the renormalized one-loop results presented by Crocce and Scoccimarro apart from the vertex renormalization. By constructing the nonlinear propagator, we analytically evaluate the nonlinear matter Power Spectra based on the first-order Born approximation of the integral expressions and compare it with those of the renormalized perturbation theory.
Antony Lewis - One of the best experts on this subject based on the ideXlab platform.
-
Full covariance of CMB and lensing reconstruction Power Spectra
Physical Review D, 2017Co-Authors: Julien Peloton, Antony Lewis, Marcel Schmittfull, Julien Carron, Oliver ZahnAbstract:CMB and lensing reconstruction Power Spectra are Powerful probes of cosmology. However, they are correlated, since the CMB Power Spectra are lensed, and the lensing reconstruction is constructed using CMB multipoles. We perform a full analysis of the auto- and cross-covariances, including polarization Power Spectra and minimum-variance lensing estimators, and compare with simulations of idealized future CMBS4 observations. Covariances sourced by fluctuations in the unlensed CMB and instrumental noise can largely be removed by using a realization-dependent subtraction of lensing reconstruction noise, leaving a relatively simple covariance model that is dominated by lensing-induced terms and well described by a small number of principal components. The correlations between the CMB and lensing Power Spectra will be detectable at the level of ∼5σ for a CMB-S4 mission, and neglecting them could underestimate some parameter error bars by several tens of percent. However, we found that the inclusion of external priors or data sets to estimate parameter error bars can make the impact of the correlations almost negligible.
-
Lensed CMB Power Spectra from all-sky correlation functions
Physical Review D, 2005Co-Authors: Anthony Challinor, Antony LewisAbstract:Weak lensing of the CMB changes the unlensed temperature anisotropy and polarization Power Spectra. Accounting for the lensing effect will be crucial to obtain accurate parameter constraints from sensitive CMB observations. Methods for computing the lensed Power Spectra using a low-order perturbative expansion are not good enough for percent-level accuracy. Nonperturbative flat-sky methods are more accurate, but curvature effects change the Spectra at the 0.3%--1% level. We describe a new, accurate, and fast, full-sky correlation-function method for computing the lensing effect on CMB Power Spectra to better than 0.1% at $l\ensuremath{\lesssim}2500$ (within the approximation that the lensing potential is linear and Gaussian). We also discuss the effect of nonlinear evolution of the gravitational potential on the lensed Power Spectra. Our fast numerical code is publicly available.
K. N. Pikalov - One of the best experts on this subject based on the ideXlab platform.
-
Deconvolutions and Power Spectra of Solar Granulation
The Dynamic Sun, 2001Co-Authors: K. N. Pikalov, A. HanslmeierAbstract:An accurate estimation of Power Spectra from 2-D white light images suggests the solving of an ill-posed problem (deconvolution) in order to restore high-frequency Spectra components depressed by the optical system of telescope and atmosphere. In this paper we address the question what are the influences of deconvolution methods to the features of restored Power Spectra. Two kinds of deconvolution techniques have been used in order to make this question clear.
-
Power Spectra of artificial granulation
Solar Physics, 1996Co-Authors: A. S. Gadun, K. N. PikalovAbstract:Two-dimensional, non-stationary hydrodynamic models of solar granulation with gray and non-gray atmospheres have been used to obtain spatial, temporal, and spatio-temporal Power Spectra. The temperature, density of kinetic energy, monochromatic intensity, integrated flux, and vertical velocity Spectra have been studied for a comparison with the Kolmogorov Power law as well as for a qualitative understanding of oscillations, which are reproduced as a result of modelling.
N. Mein - One of the best experts on this subject based on the ideXlab platform.
-
Turbulent Power Spectra of solar granulation
Astronomy and Astrophysics, 1993Co-Authors: O. Espagnet, R. Muller, T. Roudier, N. MeinAbstract:High resolution »Multichannel Subtractive Double Pass« spectrograms and white light photographs have been used to compute Power Spectra of the solar granulation. The 5 min oscillations have been carefully filtered, and the influence of the variation of the mean size of granules at the mesogranulation scale has been taken into account. It results that both the Power Spectra of velocity and intensity fluctuations, displayed in a log P − log k scale, are characteristic of a turbulent atmosphere: they present a discontinuity at 3″ = 2000 km (which corresponds to the size of a large granules) and an energy which decreases according to the Kolmogorov −5/3 Power law in the granulation range; another discontinuity, at 1″4 = 1000 km (which corresponds approximately to a Peclet number Pe = 1, for which thermal diffusion and advection are of equal importance) is present in the intensity Power spectrum, which decreases which a −17/3 Power law, in the range of sizes smaller than 1″4
Martin White - One of the best experts on this subject based on the ideXlab platform.
-
Power Spectra Estimation for Weak Lensing
The Astrophysical Journal, 2001Co-Authors: Martin WhiteAbstract:We develop a method for estimating the shear Power Spectra from weak-lensing observations and test it on simulated data. Our method describes the shear field in terms of angular Power Spectra and the cross-correlation of the two shear modes, which differ under parity transformations. Two of the three Power Spectra can be used to monitor unknown sources of noise in the data. The Power Spectra are decomposed in a model-independent manner in terms of "band Powers," which are then extracted from the data using a quadratic estimator to find the maximum of the likelihood and its local curvature (for error estimates). We test the method against simulated data from Gaussian realizations and cosmological N-body simulations. In the Gaussian case, the mean band Powers and their covariance are well recovered even for irregular (or sparsely) sampled fields. The mild non-Gaussianity of the N-body realizations causes a slight underestimation of the errors that becomes negligible for scales much larger than several arcminutes and does not bias the recovered band Powers. These techniques can also be directly applied to cosmic microwave background polarization E and B mode analyses on small fields.
