Three thermodynamically-based parametrizations of the deceleration parameter

TL;DR

This paper introduces three new, well-behaved, model-independent parametrizations of the cosmic deceleration parameter constrained by observational data, grounded in thermodynamic principles and cosmic evolution requirements.

Contribution

It proposes three novel parametrizations of q(z) that are finite at all redshifts, based on thermodynamic constraints and fixed boundary conditions, improving upon previous models.

Findings

All three parametrizations fit observational data well.

They remain finite and well-behaved across all redshifts.

The models are consistent with thermodynamic laws and cosmic structure formation.

Abstract

We propose, and constrain with the latest observational data, three model-independent parametrizations of the cosmic deceleration parameter $q(z)$. They are well behaved and stay finite at all redshifts. We construct them by fixing the value of $q$ at high redshift, $q(z \gg 1) = 1/2$ (as demanded by cosmic structure formation), and at the far future, $q(z = -1) = -1$, and smoothly interpolating $q(z)$ between them. The fixed point at $z = -1$ is not arbitrarily chosen; it readily follows from the second law of thermodynamics. This fairly reduces the ample latitude in parameterizing $q(z)$.