Unified Analysis of Cosmological Perturbations in Generalized Gravity

TL;DR

This paper develops a unified framework for analyzing cosmological perturbations in generalized gravity theories with scalar-curvature couplings, providing broad applicability to models beyond Einstein's gravity.

Contribution

It derives unified equations and solutions for scalar and tensor perturbations in generalized gravity theories with scalar-curvature couplings, extending previous analyses.

Findings

Large scale evolutions are characterized by conserved quantities similar to Einstein's gravity.

Unified treatment simplifies analysis across different generalized gravity models.

Proper gauge choices enable a consistent and simple formulation.

Abstract

In a class of generalized Einstein's gravity theories we derive the equations and general asymptotic solutions describing the evolution of the perturbed universe in unified forms. Our gravity theory considers general couplings between the scalar field and the scalar curvature in the Lagrangian, thus includes broad classes of generalized gravity theories resulting from recent attempts for the unification. We analyze both the scalar-type mode and the gravitational wave in analogous ways. For both modes the large scale evolutions are characterized by the same conserved quantities which are valid in the Einstein's gravity. This unified and simple treatment is possible due to our proper choice of the gauges, or equivalently gauge invariant combinations.