Pre-Big-Bang Cosmology and Circles in the Cosmic Microwave Background

TL;DR

This paper investigates the potential formation of circles in the cosmic microwave background caused by pre-big-bang gravitational waves, aiming to differentiate between various early universe models through their geometric signatures.

Contribution

It derives the expected properties of such circles and explores how their features vary across different pre-big-bang cosmological models, providing a method to identify their origins.

Findings

Derived size distribution and ring width of circles in CMB

Identified differences in circle properties across models

Proposed a relation between ring width and radius for detection

Abstract

We examine the possibility that circles in the cosmic microwave background could be formed by the interaction of a gravitational wave pulse emitted in some pre-big-bang phase of the universe with the last scattering surface. We derive the expected size distribution of such circles, as well as their typical ring width and (for concentric circles) angular separation. We apply these results in particular to conformal cyclic cosmology, ekpyrotic cosmology as well as loop quantum cosmology with and without inflation in order to determine how the predicted geometric properties of these circles would vary from one model to the other, and thus, if detected, could allow us to differentiate between various pre-big-bang cosmological models. We also obtain a relation between the angular ring width and the angular radius of such circles that can be used in order to determine whether or not circles observed in the cosmic microwave background are due to energetic pre-big-bang events.