Gravitational waves

To investigate gravitational radiation,
we　need　a　gauge-invariant　wave extraction.
But it have not been finished.

In the conformal slicing,
 can be considered

as the gravitational waves.

In the maximal slicing,
hij is still transverse-traceless.

We compare hij and Aij = ∂thij
between the conformal slicing and the maximal slicing.