Parity violation in pre-inflationary bounce

TL;DR

This paper investigates how a pre-inflationary bounce could lead to observable parity-violating signals in the CMB, through circularly polarized gravitational waves influenced by gravitational Chern-Simons terms.

Contribution

It introduces the calculation of circularly polarized gravitational waves caused by Chern-Simons terms in a bounce-inflation scenario, linking parity violation to pre-inflationary physics.

Findings

TB and EB correlations may be enhanced at large scales.

BB power spectrum is suppressed at the largest scales.

Parity-violating signals could serve as evidence for a pre-inflationary bounce.

Abstract

The power suppression at largest scale in the CMB TT powerspectrum might imply the occurrence of a pre-inflationary bounce. We calculate the circularly polarized gravitational wave, leaded by the gravitational Chern-Simons term which universally appears in particle physics and string theory, in an inflationary background with the pre-inflationary bounce. The circularly polarized gravitational wave will induce TB and EB correlations at CMB last scatting surface. We find that although the BB powerspectrum at largest scale is also suppressed, the TB and EB powerspectra at corresponding scales may be enhanced.