Polarized primordial gravitational waves in spatial covariant gravities

Understand

The spatial covariant gravities provide a natural way to including odd-order spatial derivative terms into the gravitational action, which breaks the parity symmetry at gravitational sector.

• A lot of parity-violating scalar-tensor theories can be mapped to the spatial covariant framework by imposing the unitary gauge.
• This provides us with a general framework for exploring the parity-violating effects in primordial gravitational waves (PGWs).
• The main purpose of this paper is to investigate the polarization of PGWs in the spatial covariant gravities and their possible observational effects.