Planck2015 results

Abstract

We study the implications of Planck data for models of dark energy (DE) and modified gravity (MG) beyond the standard cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state w(a), as well as principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints and find that it has to be below ∼2% (at 95% confidence) of the critical density, even when forced to play a role for z < 50 only. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as k-essence, f (R) theories, and coupled DE. In addition to the latest Planck data, for our main analyses, we use background constraints from baryonic acoustic oscillations, type-Ia supernovae, and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshift-space distortions and weak gravitational lensing. These additional probes are important tools for testing MG models and for breaking degeneracies that are still present in the combination of Planck and background data sets. All results that include only background parameterizations (expansion of the equation of state, early DE, general potentials in minimally-coupled scalar fields or principal component analysis) are in agreement with ΛCDM. When testing models that also change perturbations (even when the background is fixed to ΛCDM), some tensions appear in a few scenarios: the maximum one found is ∼2σ for Planck TT+lowP when parameterizing observables related to the gravitational potentials with a chosen time dependence; the tension increases to, at most, 3σ when external data sets are included. It however disappears when including CMB lensing.

Early cosmology constrained

“…This model has the advantage of requiring only two extra parameters compared to ΛCDM. It has been used extensively and in particular it was explored in the official analysis of the Planck 2013 [20] and Planck 2015 data [21]. Instead of parameterising the dark energy equation of state, w(a), the authors of [19] proposed a parametrization of the dark energy density as a function of scale factor Ω d (a).…”

“…3.2, could only obtain upper limits for the relevant parameters, adopting hard priors Ω d,e ≥ 0 and w 0 > −1 [21], we explore, for the first time, the region where w 0 < −1 and Ω d,e < 0. the results of the analysis including the effects of perturbations (CAMB implementation) is shown. This can be compared directly with the analysis performed by the Planck team.…”

“…This has been done in e.g. [21] using the Boltzmann code CAMB [22] and considering a parametrized quintessence fluid at the perturbative level, i.e. a fluid with sound speed c 2 s = 1 and no anisotropic stress.…”

Effects of neutrino mass hierarchies on dynamical dark energy models

“…Since there are dozens of different dark energy models , in this work we consider three general parametric models for DE, namely the Chevallier-PolarskiLinder (CPL) parametrization, the logarithmic model, and the Jassal-Bagla-Padmanabhan (JBP) parametric model. The dynamical models of DE have been recently constrained from other observational perspectives [60][61][62][63]. The paper is organized as follows.…”

Search for Dark Matters at Accelerators

“…• If DM was pair created after the inflationary reheating, it should have some kind of weak or super-weak interaction with the gauge particles of the SM [12] .…”