78 research outputs found
Hot and cold spots counts as probes of non-Gaussianity in the CMB
We introduce the numbers of hot and cold spots, and , 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 and , which is distinct for each of the models under
consideration. We further demonstrate that and 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
Tensor Minkowski Functionals for random fields on the sphere
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
Cosmic acceleration in a model of scalar-tensor gravitation
In this paper we consider a model of scalar-tensor theory of gravitation in
which the scalar field, determines the gravitational coupling G and has
a Lagrangian of the form, . 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
, with and that the transition
to an accelerated phase happened at a redshift of about 0.3.Comment: 12 pages, 2 figures, matches published versio
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