Phi Zeta Delta: Growth of Perturbations in Parameterized Gravity for an Einstein-de Sitter Universe

TL;DR

This paper develops a consistent parameterization of modified gravity in an Einstein-de Sitter universe to study the growth of perturbations, including effects on the ISW effect and superhorizon modes.

Contribution

It introduces a mathematically consistent parameterization at the field equation level that incorporates new scalar degrees of freedom for analyzing perturbations.

Findings

Explicit scalar degrees of freedom affect perturbation growth.

The parameterization impacts the Integrated Sachs-Wolfe effect.

Superhorizon perturbations are conserved under this framework.

Abstract

Parameterized frameworks for modified gravity are potentially useful tools for model-independent tests of General Relativity on cosmological scales. The toy model of an Einstein-de Sitter (EdS) universe provides a safe testbed in which to improve our understanding of their behaviour. We implement a mathematically consistent parameterization at the level of the field equations, and use this to calculate the evolution of perturbations in an EdS scenario. Our parameterization explicitly allows for new scalar degrees of freedom, and we compare this to theories in which the only degrees of freedom come from the metric and ordinary matter. The impact on the Integrated Sachs-Wolfe effect and canonically-conserved superhorizon perturbations is considered.