Model independent constraints on dark energy evolution from low-redshift observations

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 model-independent 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 low-redshift observations coming from supernova type Ia, baryon acoustic oscillation, H(⁠|

z

|⁠), H_0, strong-lensing time-delay as well as the megamaser observations for angular diameter distances. We confirm the tensions with Λ cold dark matter model for low-redshifts observations. The present value of the equation of state for the dark energy has to be phantom-like and for other redshifts, it has to be either phantom or should have a phantom crossing. For lower values of Ωm0, multiple phantom crossings are expected. This poses serious challenges for single, non-interacting 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_{\mathrm{ s}}^2 \lt 0

| due to constraints from low-redshift observations.

Note:

14 pages, LateX, MNRAS style, 7 Figures, revised version with added figure and discussions. Accepted for publication in MNRAS

cosmological parameters
dark energy
cosmology: observations
cosmology: theory
fluid: model
phantom: crossing
dark energy: fluid
oscillation: acoustic
field theory: scalar
velocity: acoustic

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