Correlation between opposite-helicity gravitons: Imprints on gravity-wave and microwave backgrounds

TL;DR

This paper explores how correlations between opposite-helicity gravitons could produce observable polarization effects in gravitational waves and CMB, revealing potential parity violation signatures in the early universe.

Contribution

It uncovers a new effect of opposite-helicity graviton correlations, linking parity violation to observable polarization and anisotropy signatures in gravitational wave and CMB data.

Findings

Opposite-helicity graviton correlations can induce polarization in primordial gravitational waves.

Spin 4 correlations relate to same-direction gravitons, spin zero to opposite directions.

Potential observable effects include enhanced B-mode polarization in CMB and standing wave signatures in gravitational wave detectors.

Abstract

We examine some of the roots of parity violation for gravitons and uncover a closely related new effect: correlations between right and left handed gravitons. Such correlators have spin 4 if they involve gravitons moving along the same direction, and spin zero for gravitons moving with opposite directions. In the first case, the most immediate implication would be a degree of linear polarization for the tensor vacuum fluctuations, which could be seen by gravity wave detectors sensitive enough to probe the primordial background, its degree of polarization and anisotropies. Looking at the anisotropy of the gravity waves linear polarization we identify the parity respecting and violating components of the effect. The imprint on the CMB temperature and polarization would be more elusive, since it averages to zero in the two-point functions, appearing only in their cosmic variance or in fourth order correlators. In contrast, spin zero correlations would have an effect on the two point function of the CMB temperature and polarization, enhancing the $BB$ component if they were anti-correlations. Such correlations represent an amplitude for the production of standing waves, as first envisaged by Grishchuk, and could also leave an interesting signature for gravity wave detectors.