[Users] Simulating hyperbolic encounters

Santiago Jaraba Gómez santiago.jaraba at uam.es
Tue Feb 23 05:53:18 CST 2021

Hi everyone,

I am a PhD student at the IFT in Madrid. I am trying to adapt the
par/arxiv-1111.3344 /bbh.par parameter file to a hyperbolic encounter with
an initial separation of 100M. In fact, my problem is very similar to the
one here:

Learning from the GW150914.rpar parameter file, I have turned the bbh.par
into a .rpar file, so that I can automatically set some parameters such as
the initial positions, momenta, masses, etc. In addition, I have set the
boundaries to 768 to accommodate the new initial positions x = ±50 and
increased the refinement levels from 7 to 10, increasing a bit the
resolution of the finest grid (from 2/2^6=0.03125 to 12.8/2^9=0.025). I
have also disabled all the HDF5 output as well as the 180º rotating
symmetry, since I will later want to use it for different masses, and
enabled the QuasiLocalMeasures thorn. Finally, by following the advice for
the mentioned doubt of February 2020, I have increased the parameters
TwoPunctures::npoints_A,B,phi to 50, 50 and 20, respectively.

I thought that I had it, since the simulation was successfully running,
even past the point of closest approach. However, shortly after that, the
parameter "ML_BSSN::trK norm2" that the output showed abruptly turned to
-nan and the simulation crashed. Could anyone help me find the problem? I
thought it might be the resolution, but the bbh.par has a bit worse finest
grid resolution and it runs smoothly, even with stronger fields involved.
Could the problem be in the initial conditions generated by TwoPunctures at
such large distances?

I attach the .rpar file in case it helps. I am very new to the
Einstein Toolkit, so I might very well have overlooked something relevant.

Thank you in advance.

Best regards,
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