Gravitational wave modes in matter

Understand

A general linear gauge-invariant equation for dispersive gravitational waves (GWs) propagating in matter is derived.

• This equation describes, on the same footing, both the usual tensor modes and the gravitational modes strongly coupled with matter.
• It is shown that the effect of matter on the former is comparable to diffraction and therefore negligible within the geometrical-optics approximation.
• However, this approximation is applicable to modes strongly coupled with matter due to their large refractive index.