924 research outputs found
Constraints on Dark Energy state equation with varying pivoting redshift
We assume the DE state equations w(a) = w_0+w_a(a_p-a), and study the
dependence of the constraints on w_0 and w_a coefficients on the pivoting
redshift 1+z_p=1/a_p. Coefficients are fitted to data including WMAP7, SNIa
(Union 2.1), BAO's (including WiggleZ and SDSS results) and H_0 constraints.
The fitting algorithm is CosmoMC. We find specific differences between the
cases when neutrino mass is allowed or disregarded. More in detail: i) The z_p
value yielding uncorrelated constraints on w_0 and w_a is different in the two
cases, holding ~0.25 and ~0.35, respectively. (ii) If we consider the intervals
allowed to w_0, we find that they shift when z_p increases, in opposite
directions for vanishing or allowed neutrino mass. This leads to no overlap
between 1sigma intervals already at z_p >~0.4. (iii) The known effect that a
more negative state parameter is required to allow for neutrino mass displays
its effects on w_a, rather than on w_0. (iv) The w_0-w_a constraints found by
using any pivot z_p can be translated into constraints holding at a specific
z_p value (0 or the z_p where errors are uncorrelated). When we do so, error
ellipses exhibit a satisfactory overlap.Comment: 13 pages, 7 figures, 2 table
Spectra of dynamical Dark Energy cosmologies from constant-w models
WMAP5 and related data have greatly restricted the range of acceptable
cosmologies, by providing precise likelihood ellypses on the the w_0-w_a plane.
We discuss first how such ellypses can be numerically rebuilt, and present then
a map of constant-w models whose spectra, at various redshift, are expected to
coincide with acceptable models within ~1%
ISW-LSS cross-correlation in coupled Dark Energy models with massive neutrinos
We provide an exhaustive analysis of the Integrated Sach-Wolfe effect (ISW)
in the context of coupled Dark Energy cosmologies where a component of massive
neutrinos is also present. We focus on the effects of both the coupling between
Dark Matter and Dark Energy and of the neutrino mass on the cross-correlation
between galaxy/quasar distributions and ISW effect. We provide a simple
expression to appropriately rescale the galaxy bias when comparing different
cosmologies. Theoretical predictions of the cross-correlation function are then
compared with observational data. We find that, while it is not possible to
distinguish among the models at low redshifts, discrepancies between coupled
models and CDM increase with . In spite of this, current data alone
seems not able to distinguish between coupled models and CDM. However,
we show that upcoming galaxy surveys will permit tomographic analysis which
allow to better discriminate among the models. We discuss the effects on
cross-correlation measurements of ignoring galaxy bias evolution, b(z), and
magnification bias correction and provide fitting formulae for b(z) for the
cosmologies considered. We compare three different tomographic schemes and
investigate how the expected signal to noise ratio, snr, of the ISW-LSS
cross-correlation changes when increasing the number of tomographic bins. The
dependence of snr on the area of the survey and the survey shot noise is also
discussed.Comment: 18 pages, 23 figures. Several major extensions. New sections and
figures was added. ApJ in prin
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