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

TL;DR

This study uses a model-independent cosmographic approach with Pade approximation to analyze low-redshift observations, revealing tensions with the standard DM model and challenging simple dark energy models due to complex evolution and stability constraints.

Contribution

It introduces a Pade approximation-based cosmographic method for constraining dark energy evolution from low-redshift data, highlighting the need for multiple dark energy behaviors and ruling out certain fluid models.

Findings

Tensions with DM at low redshifts.

Dark energy exhibits phantom or crossing behavior.

Single scalar field models are insufficient for all redshifts.

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 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 SNIa, BAO, $H(z)$, $H_{0}$ , strong-lensing time-delay as well as the Megamaser observations for angular diameter distances. We confirm the tensions with $\Lambda$CDM 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 $\Omega_{m0}$, multiple phantom crossings are expected. This poses serious challenges for single, non-interacting scalar field models for dark energy. We derive constraints on the {\it statefinders} $(r,s)$ and these constraints show that a single dark energy model cannot fit data for the whole redshift range $0\leq z\leq 2$: in other words, we need multiple dark energy behaviors 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 low-redshift observations.