34 research outputs found
Bayesian Evidence against Harrison-Zel'dovich spectrum in tension cosmology
Current cosmological constraints on the scalar spectral index of primordial
fluctuations in the CDM model have excluded the minimal
scale-invariant Harrison-Zel'dovich model (; hereafter HZ) at high
significance, providing support for inflation. In recent years, however, some
tensions have emerged between different cosmological datasets that, if not due
to systematics, could indicate the presence of new physics beyond the
CDM model. In the light of these developments, we evaluate the
Bayesian evidence against HZ in different data combinations and model
extensions. Considering only the Planck temperature data, we find inconclusive
evidence against HZ when including variations in the neutrino number and/or the Helium abundance . Adding the Planck polarization
data, on the other hand, yields strong evidence against HZ in the extensions we
considered. Perhaps most interestingly, Planck temperature data combined with
local measurements of the Hubble constant give as the most probable model an HZ
spectrum, with additional neutrinos. However, with the inclusion of
polarisation, standard CDM is once again preferred, but the HZ model
with extra neutrinos is not strongly disfavored. The possibility of fully
ruling out the HZ spectrum is therefore ultimately connected with the solution
to current tensions between cosmological datasets. If these tensions are
confirmed by future data, then new physical mechanisms could be at work and an
HZ spectrum could still offer a valid alternative.Comment: 14 pages, 1 figur
CMB lensing reconstruction in the presence of diffuse polarized foregrounds
Comment: 22 pages, 24 figures; With a moderate revision of the original version, as published in JCA
Measuring primordial gravitational waves from CMB B-modes in cosmologies with generalized expansion histories
We evaluate our capability to constrain the abundance of primordial tensor
perturbations in cosmologies with generalized expansion histories in the epoch
of cosmic acceleration. Forthcoming satellite and sub-orbital experiments
probing polarization in the CMB are expected to measure the B-mode power in CMB
polarization, coming from PGWs on the degree scale, as well as gravitational
lensing on arcmin scales; the latter is the main competitor for the measurement
of PGWs, and is directly affected by the underlying expansion history,
determined by the presence of a DE component. In particular, we consider early
DE possible scenarios, in which the expansion history is substantially modified
at the epoch in which the CMB lensing is most relevant. We show that the
introduction of a parametrized DE may induce a variation as large as 30% in the
ratio of the power of lensing and PGWs on the degree scale. We find that
adopting the nominal specifications of upcoming satellite measurements the
constraining power on PGWs is weakened by the inclusion of the extra degrees of
freedom, resulting in a reduction of about 10% of the upper limits on r in
fiducial models with no GWs, as well as a comparable increase in the error bars
in models with non-zero r. Moreover, we find that the inclusion of sub-orbital
CMB experiments, capable of mapping the B-mode power up to the angular scales
affected by lensing, can restore the forecasted performances with a
cosmological constant. Finally, we show how the combination of CMB data with
Type Ia SNe, BAO and Hubble constant allows to constrain simultaneously r and
the DE quantities in the parametrization we consider, consisting of present
abundance and first redshift derivative of the energy density. We compare this
study with results obtained using the forecasted lensing potential measurement
precision from CMB satellite observations, finding consistent results.Comment: 17 pages, 9 figures, accepted for publication by JCAP. Modified
version after the referee's comment
No evidence for extensions to the standard cosmological model
CITATION: Heavens, A., et al. 2017. No evidence for extensions to the standard cosmological model. Physical Review Letters, 119(10):1-5, doi:10.1103/PhysRevLett.119.101301.The original publication is available at https://journals.aps.org/prlWe compute the Bayesian evidence for models considered in the main analysis of Planck cosmic microwave background data. By utilizing carefully defined nearest-neighbor distances in parameter space, we reuse the Monte Carlo Markov chains already produced for parameter inference to compute Bayes factors B for many different model-data set combinations. The standard 6-parameter flat cold dark matter model with a cosmological constant (ΛCDM) is favored over all other models considered, with curvature being mildly favored only when cosmic microwave background lensing is not included. Many alternative models are strongly disfavored by the data, including primordial correlated isocurvature models (lnB=−7.8), nonzero scalar-to-tensor ratio (lnB=−4.3), running of the spectral index (lnB=−4.7), curvature (lnB=−3.6), nonstandard numbers of neutrinos (lnB=−3.1), nonstandard neutrino masses (lnB=−3.2), nonstandard lensing potential (lnB=−4.6), evolving dark energy (lnB=−3.2), sterile neutrinos (lnB=−6.9), and extra sterile neutrinos with a nonzero scalar-to-tensor ratio (lnB=−10.8). Other models are less strongly disfavored with respect to flat ΛCDM. As with all analyses based on Bayesian evidence, the final numbers depend on the widths of the parameter priors. We adopt the priors used in the Planck analysis, while performing a prior sensitivity analysis. Our quantitative conclusion is that extensions beyond the standard cosmological model are disfavored by Planck data. Only when newer Hubble constant measurements are included does ΛCDM become disfavored, and only mildly, compared with a dynamical dark energy model (lnB∼+2).Publisher's versio