[Users] output from WeylScal

[Eloisa Bentivegna]

On Feb 1, 2012, at 3:12 AM, Jose Fiestas Iquira wrote:

> Dear all,
> I am using WeylScal for BH binary coalescence, and I am obtaining 'weylscal4::psi4r...' and 'weylscal4::psi4i ...' files, with which I could plot the wave against distance/time.
> Could somebody advise me how to get the energy emission due to grav. waves from the WeylScal output? I would like to construct a plot: GW Energy vs. distance/time.

Hi Jose,

there's a couple of things to keep in mind:

1) In broad terms, there is no notion of gravitational-wave energy density; one can at best associate a mass with the whole spatial hypersurface, but not state how much of this is in gravitational waves or where it is localized;
2) Under reasonable assumptions, the radiated power at infinity can be expressed in terms of the Weyl scalars. You'd probably best start learning about this is in one of the numerical-relativity textbooks: either section 8.9 of <http://books.google.de/books?id=4hDvRvVJeEIC&dq=alcubierre&hl=de&sa=X&ei=GBopT--LC87ItAbI-b3FAQ&ved=0CDIQ6AEwAA> or section 9.4 of <http://books.google.de/books?id=dxU1OEinvRUC&dq=baumgarte&hl=de&source=gbs_navlinks_s> (notice that this is still a function of time only -- no localization);
3) If you're just interested in how much energy leaves the system during the merger, you may be better off subtracting the final horizon mass (given by AHFinderDirect) from the ADM mass (given by TwoPunctures).

Let me know if this isn't clear enough!
Eloisa