The Origin of Structures in Generalized Gravity

TL;DR

This paper explores how generalized gravity theories can explain the quantum origin and classical evolution of cosmic structures, linking early universe quantum fluctuations to large-scale structures and CMB anisotropies.

Contribution

It presents a unified framework for describing the quantum generation and classical evolution of scalar and tensor structures in generalized gravity theories.

Findings

Quantum fluctuations expand to macroscopic scales during accelerated early universe expansion.

Fluctuation amplitudes remain conserved during their outside-horizon evolution.

The model explains large-scale cosmic structures and CMB anisotropies.

Abstract

In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we can describe the quantum generation and the classical evolution of both the scalar and tensor structures in a simple and unified manner. An accelerated expansion phase based on the generalized gravity in the early universe drives microscopic quantum fluctuations inside a causal domain to expand into macroscopic ripples in the spacetime metric on scales larger than the local horizon. Following their generation from quantum fluctuations, the ripples in the metric spend a long period outside the causal domain. During this phase their evolution is characterized by their conserved amplitudes. The evolution of these fluctuations may lead to the observed large scale structures of the universe and anisotropies in the cosmic microwave background radiation.