Perturbations with respect to the inverse metric

[alej...@gmail.com]

Hi all,

My question is about perturbations. In certain contexts, it is more useful to work with the inverse metric instead of the metric itself.

Is there any way to do essentially the same thing that DefMetricPerturbation does but with the inverse metric? (i.e., to have the expansion of the curvatures, the sqrt{g} and so on with respect to h^{ab}, where h^{ab} = g^{ab} - (background g)^{ab}).

Thanks!

Best,

Alejandro

[Jose]

Hi,

No, xPert is designed to work with perturbations of the metric, and not with perturbations of its inverse.

It's possible that there is some trick that allows inferring formulas for one from formulas for the other, involving for example changes of signs in the result, following parity of the perturbation order, but I'm not really sure.

If you find out how to handle this, please report it back here!

Thanks,

Jose.