[Users] outer boundary conditions

[Eloisa Bentivegna]

On May 29, 2013, at 3:17 PM, Comer Duncan wrote:

> Hi Eric,
> 
> Thanks for your reply.
> 
> I found a reference to an old paper by Vulcanov in which he mentions a thorn he calls Cosmo which is purported to begin to include cosmological backgrounds and expanding outer bc.  However, I can not seem to find such nowadays in ET.  Do you remember it? If so, is it now defunct and/or inadequate?  
> 
> Treating the expanding background as an asymptotic bc with a gauge choice is something I thought about.  I was just thinking of running some problems using McLachlan with say FRW outer bc and was wondering whether McLachlan has been used by anyone in this context? I have not seen such.

Hi Comer,

if the work from Vulcanov is the one I'm thinking of (http://arxiv.org/abs/gr-qc/0210006), then that involved ODEs (assuming that all the 3+1 quantities were spatial constants), so no boundary conditions were required. You can find an example of a full 3D evolution of a cosmological model with the ET in the ET paper (http://arxiv.org/abs/1111.3344), and the corresponding parameter file under the par/arXiv:1111.3344/cosmology/ directory in your ET tree.

Using FLRW only as a boundary condition is a completely different story, which entails, among other things, figuring out whether that specification is compatible with the evolution equations. Which sort of spacetime do you have in mind? I suggest straightening out the formulation of the problem before turning to the technical question of how to implement this in Cactus.

Best,
Eloisa