78 research outputs found

    Tensor Minkowski Functionals for random fields on the sphere

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    We generalize the translation invariant tensor-valued Minkowski Functionals which are defined on two-dimensional flat space to the unit sphere. We apply them to level sets of random fields. The contours enclosing boundaries of level sets of random fields give a spatial distribution of random smooth closed curves. We obtain analytic expressions for the ensemble expectation values for the matrix elements of the tensor-valued Minkowski Functionals for isotropic Gaussian and Rayleigh fields. We elucidate the way in which the elements of the tensor Minkowski Functionals encode information about the nature and statistical isotropy (or departure from isotropy) of the field. We then implement our method to compute the tensor-valued Minkowski Functionals numerically and demonstrate how they encode statistical anisotropy and departure from Gaussianity by applying the method to maps of the Galactic foreground emissions from the PLANCK data.Comment: 1+23 pages, 5 figures, Significantly expanded from version 1. To appear in JCA

    Hot and cold spots counts as probes of non-Gaussianity in the CMB

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    We introduce the numbers of hot and cold spots, nhn_h and ncn_c, of excursion sets of the CMB temperature anisotropy maps as statistical observables that can discriminate different non-Gaussian models. We numerically compute them from simulations of non-Gaussian CMB temperature fluctuation maps. The first kind of non-Gaussian model we study is the local type primordial non-Gaussianity. The second kind of models have some specific form of the probability distribution function from which the temperature fluctuation value at each pixel is drawn, obtained using HEALPIX. We find the characteristic non-Gaussian deviation shapes of nhn_h and ncn_c, which is distinct for each of the models under consideration. We further demonstrate that nhn_h and ncn_c carry additional information compared to the genus, which is just their linear combination, making them valuable additions to the Minkowski Functionals in constraining non-Gaussianity.Comment: 17 pages, accepted for publication in Ap

    Cosmic acceleration in a model of scalar-tensor gravitation

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    In this paper we consider a model of scalar-tensor theory of gravitation in which the scalar field, ϕ\phi determines the gravitational coupling G and has a Lagrangian of the form, Lϕ=V(ϕ)1μϕμϕ\mathcal{L}_{\phi} =-V(\phi)\sqrt{1 - \partial_{\mu}\phi\partial^{\mu}\phi}. We study the cosmological consequence of this theory in the matter dominated era and show that this leads to a transition from an initial decelerated expansion to an accelerated expansion phase at the present epoch. Using observational constraints, we see that the effective equation of state today for the scalar field turns out to be pϕ=wϕρϕp_{\phi}=w_{\phi}{\rho}_{\phi}, with wϕ=0.88w_{\phi}=-0.88 and that the transition to an accelerated phase happened at a redshift of about 0.3.Comment: 12 pages, 2 figures, matches published versio