54 research outputs found
CMB and BAO constraints for an induced gravity dark energy model with a quartic potential
We study the predictions for structure formation in an induced gravity dark
energy model with a quartic potential. By developing a dedicated
Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous
cosmology and of linear perturbations without using any parametrization. By
evolving linear perturbations with initial conditions in the radiation era, we
accurately recover the quasi-static analytic approximation in the matter
dominated era. We use Planck 2013 data and a compilation of baryonic acoustic
oscillation (BAO) data to constrain the coupling to the Ricci
curvature and the other cosmological parameters. By connecting the
gravitational constant in the Einstein equation to the one measured in a
Cavendish-like experiment, we find at 95% CL with Planck 2013
and BAO data. This is the tightest cosmological constraint on and on
the corresponding derived post-Newtonian parameters. Because of a degeneracy
between and the Hubble constant , we show how larger values for
are allowed, but not preferred at a significant statistical level,
when local measurements of are combined in the analysis with Planck 2013
data.Comment: 13 pages, 7 figure
Cosmological constraints on induced gravity dark energy models
We study induced gravity dark energy models coupled with a simple monomial
potential and a positive exponent . These simple
potentials lead to viable dark energy models with a weak dependence on the
exponent, which characterizes the accelerated expansion of the cosmological
model in the asymptotic attractor, when ordinary matter becomes negligible. We
use recent cosmological data to constrain the coupling to the Ricci
curvature, under the assumptions that the scalar field starts at rest deep in
the radiation era and that the gravitational constant in the Einstein equations
is compatible with the one measured in a Cavendish-like experiment. By using
2015 data only, we obtain the 95 % CL bound for
, which is further tightened to by adding Baryonic
Acoustic Oscillations (BAO) data. This latter bound improves by % the
limit obtained with the 2013 data and the same compilation of BAO
data. We discuss the dependence of the and on
.Comment: 16 pages, 10 figure
On the ISW-cluster cross-correlation in future surveys
We investigate the cosmological information contained in the
cross-correlation between the Integrated Sachs-Wolfe (ISW) of the Cosmic
Microwave Background (CMB) anisotropy pattern and galaxy clusters from future
wide surveys. Future surveys will provide cluster catalogues with a number of
objects comparable with galaxy catalogues currently used for the detection of
the ISW signal by cross-correlation with the CMB anisotropy pattern. By
computing the angular power spectra of clusters and the corresponding
cross-correlation with CMB, we perform a signal-to-noise ratio (SNR) analysis
for the ISW detection as expected from the eROSITA and the Euclid space
missions. We discuss the dependence of the SNR of the ISW-cluster
cross-correlation on the specifications of the catalogues and on the reference
cosmology. We forecast that the SNRs for ISW-cluster cross-correlation are
alightly smaller compared to those which can be obtained from future galaxy
surveys but the signal is expected to be detected at high significance, i.e.
more than . We also forecast the joint constraints on parameters
of model extensions of the concordance CDM cosmology by combining CMB
and the ISW-cluster cross-correlation.Comment: 12 pages, 10 figures. Matches version accepted in MNRA
CMB anisotropies generated by a stochastic background of primordial magnetic fields with non-zero helicity
We consider the impact of a stochastic background of primordial magnetic
fields with non-vanishing helicity on CMB anisotropies in temperature and
polarization. We compute the exact expressions for the scalar, vector and
tensor part of the energy-momentum tensor including the helical contribution,
by assuming a power-law dependence for the spectra and a comoving cutoff which
mimics the damping due to viscosity. We also compute the parity-odd correlator
between the helical and non-helical contribution which generate the TB and EB
cross-correlation in the CMB pattern. We finally show the impact of including
the helical term on the power spectra of CMB anisotropies up to multipoles with
ell ~ O(10^3)$.Comment: 25 pages, 30 figure
Larger value for H0 by an evolving gravitational constant
We provide further evidence that a massless cosmological scalar field with a nonminimal coupling to the Ricci curvature of the type
M
2
pl
(
1
+
ξ
σ
n
/
M
n
pl
)
alleviates the existing tension between local measurements of the Hubble constant and its inference from cosmic microwave background anisotropies and baryonic acoustic oscillations data in the presence of a cosmological constant. In these models, the expansion history is modified compared to
Λ
CDM
at early time, mimicking a change in the effective number of relativistic species, and gravity weakens after matter-radiation equality. Compared to
Λ
CDM
, a quadratic (
n
=
2
) coupling increases the Hubble constant when Planck 2018 (alone or in combination with BAO and SH0ES) measurements data are used in the analysis. Negative values of the coupling, for which the scalar field decreases, seem favored and consistency with the Solar System can be naturally achieved for a large portion of the parameter space without the need of any screening mechanism. We show that our results are robust to the choice of
n
, also presenting the analysis for
n
=
4
- …