Observational constraints on the tilted spatially-flat and the untilted nonflat $\phi$CDM dynamical dark energy inflation models

TL;DR

This study uses Planck 2015 data combined with other cosmological observations to constrain tilted flat and untilted nonflat $$CDM dark energy models, finding evidence for a slightly closed universe and that dynamical dark energy models are compatible with current data.

Contribution

It provides new constraints on tilted flat and untilted nonflat $$CDM models using multiple observational datasets, highlighting the significance of nonflatness and dynamical dark energy.

Findings

Nonflat untilted $$CDM model favors a closed universe with ~0.67% curvature.

Flat tilted $$CDM model fits data slightly better than flat $ m{ extLambda}$CDM.

Nonflat tilted $$CDM aligns better with DES $\sigma_8$ constraints but less with Planck high-$ extbf{ extit{l}}$ CMB data.

Abstract

We constrain spatially-flat tilted and nonflat untilted scalar field ($\phi$) dynamical dark energy inflation ($\phi$CDM) models by using Planck 2015 cosmic microwave background (CMB) anisotropy measurements and recent baryonic acoustic oscillation distance observations, Type Ia supernovae apparent magnitude data, Hubble parameter measurements, and growth rate data. We assume an inverse power-law scalar field potential energy density $V(\phi)=V_0 \phi^{-\alpha}$. We find that the combination of the CMB data with the four non-CMB data sets significantly improves parameter constraints and strengthens the evidence for nonflatness in the nonflat untilted $\phi$CDM case from $1.8\sigma$ for the CMB measurements only to more than $3.1\sigma$ for the combined data. In the nonflat untilted $\phi$CDM model current observations favor a spatially closed universe with spatial curvature contributing about two-thirds of a percent of the present cosmological energy budget. The flat tilted $\phi$CDM model is a 0.4$\sigma$ better fit to the data than is the standard flat tilted $\Lambda$CDM model: current data allow for the possibility that dark energy is dynamical. The nonflat tilted $\phi$CDM model is in better accord with the Dark Energy Survey bounds on the rms amplitude of mass fluctuations now ($\sigma_8$) as a function of the nonrelativistic matter density parameter now ($\Omega_m$) but it does not provide as good a fit to the larger-multipole Planck 2015 CMB anisotropy data as does the standard flat tilted $\Lambda$CDM model. A few cosmological parameter value measurements differ significantly when determined using the tilted flat and the untilted nonflat $\phi$CDM models, including the cold dark matter density parameter and the reionization optical depth.