264 research outputs found
Null tests of the standard model using the linear model formalism
We test both the FLRW geometry and CDM cosmology in a model
independent way by reconstructing the Hubble function , the comoving
distance and the growth of structure using the most
recent data available. We use the linear model formalism in order to optimally
reconstruct the latter cosmological functions, together with their derivatives
and integrals. We then evaluate four of the null tests available in literature:
by Sahni et al., by Zunckel \& Clarkson, by Clarkson et
al., and by Nesseris \& Sapone. For all the four tests we find agreement,
within the errors, with the standard cosmological model.Comment: 8 pages, 7 figures and 1 tabl
Intrinsic uncertainty on the nature of dark energy
We argue that there is an intrinsic noise on measurements of the equation of
state parameter from large-scale structure around us. The presence
of the large-scale structure leads to an ambiguity in the definition of the
background universe and thus there is a maximal precision with which we can
determine the equation of state of dark energy. To study the uncertainty due to
local structure, we model density perturbations stemming from a standard
inflationary power spectrum by means of the exact Lema\^{i}tre-Tolman-Bondi
solution of Einstein's equation, and show that the usual distribution of matter
inhomogeneities in a CDM cosmology causes a variation of -- as
inferred from distance measures -- of several percent. As we observe only one
universe, or equivalently because of the cosmic variance, this uncertainty is
systematic in nature.Comment: 12 pages, 3 figures. Version as accepted for publication in Physics
of the Dark Universe (Open Access
Constraining the halo mass function with observations
The abundances of dark matter halos in the universe are described by the halo
mass function (HMF). It enters most cosmological analyses and parametrizes how
the linear growth of primordial perturbations is connected to these abundances.
Interestingly, this connection can be made approximately cosmology independent.
This made it possible to map in detail its near-universal behavior through
large-scale simulations. However, such simulations may suffer from systematic
effects, especially if baryonic physics is included. In this paper we ask how
well observations can constrain directly the HMF. The observables we consider
are galaxy cluster number counts, galaxy cluster power spectrum and lensing of
type Ia supernovae. Our results show that DES is capable of putting the first
meaningful constraints on the HMF, while both Euclid and J-PAS can give
stronger constraints, comparable to the ones from state-of-the-art simulations.
We also find that an independent measurement of cluster masses is even more
important for measuring the HMF than for constraining the cosmological
parameters, and can vastly improve the determination of the halo mass function.
Measuring the HMF could thus be used to cross-check simulations and their
implementation of baryon physics. It could even, if deviations cannot be
accounted for, hint at new physics.Comment: v2: small improvements to the text; matches accepted version. 13
pages, 8 figure
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