[Users] question about ML_CCZ4 parameters

[Bruno Giacomazzo]

Together with a student of mine we are trying to use the CCZ4 formulation
implemented in McLachlan.  We saw that most parameters are the same as in
BSSN, but there are damping factors that need to be selected.

In Alic et al 2013 (https://link.aps.org/doi/10.1103/PhysRevD.88.064049)
they mention 3 damping factors (k1, k2, and k3), but in the param.ccl
of McLachlan/ML_CCZ4 only k1 and k2 are mentioned (assuming they are the
same).

Is it because k3 is hardcoded to the value suggested in Alic et al 2013? Or
does McLachlan/ML_CCZ4 use a different set of evolution equations (in which
case, is there a reference)?

We were able to find some example parameter files (for example the ones
from the Parma group
https://einstein.pr.infn.it/gravity/Research/BNS2015.html) and we found
that they used indeed k1 and k2 from Alic et al 2013:
ML_CCZ4::dampk1 = 0.05
ML_CCZ4::dampk2 = 0

We also saw that they added  ML_CCZ4::ML_Theta to the Dissipation vars and
set
ML_CCZ4::apply_dissipation   = "never".
The other parameters look the same as when using BSSN.

Since I never used ML_CCZ4 I want to be sure that I'm setting the
parameters correctly and the damping factors seem to be the most delicate
point.

Thanks,
Bruno

-- 

Prof. Bruno Giacomazzo
Department of Physics
University of Milano-Bicocca
Piazza della Scienza 3
20126 Milano
Italy

email: bruno.giacomazzo at unimib.it
phone: (+39) 02 6448 2321
web: http://www.brunogiacomazzo.org

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