A single parameterization for dark energy and modified gravity models

Abstract

Perhaps the most explored hypothesis for the accelerated cosmic expansion rate arises in the context of extra fields or modifications to General Relativity. A prevalent approach is to parameterize the expansion history through the equation of state, $\omega(z)$. We present a parametric form for $\omega(z)$ that can reproduce the generic behavior of the most widely used physical models for accelerated expansion with infrared corrections. The present proposal has at most 3 free parameters which can be mapped back to specific archetypal models for dark energy. We analyze in detail how different combinations of data can constrain the specific cases embedded in our form for $\omega(z)$. We implement our parametric equation for $\omega(z)$ to observations from CMB, the luminous distance of SNeIa, cosmic chronometers, and baryon acoustic oscillations identified in galaxies and in the Lymann-$\alpha$ forest. We find that the parameters can be well constrained by using different observational data sets. Our findings point to an oscillatory behavior consistent with an $f(R)$-like model or an unknown combination of scalar fields. When we let the three parameters vary freely, we find an EoS which oscillates around the phantom-dividing line, and, with over 99$\%$ of confidence, the cosmological constant solution is disfavored.