Modelindependent constraints on dark energy evolution from lowredshift observations
Abstract
Knowing the late time evolution of the Universe and finding out the causes for this evolution are the important challenges of modern cosmology. In this work, we adopt a modelindependent cosmographic approach and approximate the Hubble parameter considering the Pade approximation which works better than the standard Taylor series approximation for z > 1. With this, we constrain the late time evolution of the Universe considering lowredshift observations coming from supernova type Ia, baryon acoustic oscillation, H(z), H_{0}, stronglensing timedelay as well as the megamaser observations for angular diameter distances. We confirm the tensions with Λ cold dark matter model for lowredshifts observations. The present value of the equation of state for the dark energy has to be phantomlike and for other redshifts, it has to be either phantom or should have a phantom crossing. For lower values of Ω_{m0}, multiple phantom crossings are expected. This poses serious challenges for single, noninteracting scalar field models for dark energy. We derive constraints on the statefinders (r, s) and these constraints show that a single dark energy model cannot fit data for the whole redshift range 0 ≤ z ≤ 2: in other words, we need multiple dark energy behaviours for different redshift ranges. Moreover, the constraint on sound speed for the total fluid of the Universe, and for the dark energy fluid (assuming them being barotropic), rules out the possibility of a barotropic fluid model for unified dark sector and barotropic fluid model for dark energy, as fluctuations in these fluids are unstable as c_{ s}^2 < 0 due to constraints from lowredshift observations.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2019
 DOI:
 10.1093/mnras/stz176
 arXiv:
 arXiv:1806.03943
 Bibcode:
 2019MNRAS.484.4484C
 Keywords:

 cosmological parameters;
 dark energy;
 cosmology: observations;
 cosmology: theory;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 14 pages, LateX, MNRAS style, 7 Figures, revised version with added figure and discussions. Accepted for publication in MNRAS