CMB power spectrum for emergent scenario and slow expansion in scalar-tensor theory of gravity

TL;DR

This paper investigates the stability of the Einstein static universe within scalar-tensor gravity, explores emergent and slow expansion scenarios, and compares their primordial power spectra and CMB predictions to the standard ΛCDM model.

Contribution

It provides analytical approximations of the primordial power spectrum for emergent scenarios and compares their CMB spectra with ΛCDM, highlighting differences at large scales.

Findings

Both scenarios' spectra match ΛCDM at small scales.

Emergent scenario spectra are lower than ΛCDM at large scales.

The Einstein static universe can be stable under certain conditions.

Abstract

We analyze the stability of the Einstein static universe in scalar-tensor theory of gravity, and find it can be stable against both scalar and tensor perturbations under certain conditions. By assuming the emergent scenario originating from an Einstein static state, followed by an instantaneous transition to an inflationary phase, we study and obtain the analytical approximations of the primordial power spectrum for the emergent scenario. Then, we plot the primordial power spectrum and CMB TT-spectrum of the emergent scenario and the slow expansion scenario. These figures show that both of these spectra for the slow expansion scenario are the same as that for $\Lambda$CDM, and the spectra of the emergent scenario are lower than that for $\Lambda$CDM at large scales.