Exploring the low redshift universe: two parametric models for effective pressure

TL;DR

This paper introduces two parametric models for effective pressure to explore deviations from the standard $ ext{Lambda}$CDM model at low redshift, using observational data to suggest a possible phantom dark energy scenario.

Contribution

It proposes novel parametric models for non-constant effective pressure and constrains them with observational data, revealing potential phantom dark energy behavior.

Findings

Hints of $ ext{w}_{de} < -1$ from data fitting

Models recover quintessence and phantom scalar fields

Potential deviation from $ ext{Lambda}$CDM at low redshift

Abstract

Astrophysical observations have put unprecedentedly tight constraints on cosmological theories. The $\Lambda$CDM model, mathematically simple and fits observational data-sets well, is preferred for explaining the behavior of universe. But many basic features of the dark sectors are still unknown, which leaves rooms for various nonstandard cosmological hypotheses. As the pressure of cosmological constant dark energy is unvarying, ignoring contributions from radiation and curvature terms at low redshift, the effective pressure keeps constant. In this paper, we propose two parametric models for non-constant effective pressure in order to study the tiny deviation from $\Lambda$CDM at low redshift. We recover our phenomenological models in the scenarios of quintessence and phantom fields, and explore the behavior of scalar field and potential. We constrain our model parameters with SNe Ia and BAO observations, and detect subtle hints of $\omega_{de}<-1$ from the data fitting results of both models, which indicates possibly a phantom dark energy scenario at present.