Dear all,
please find the minutes for today's call below.
@Bishop: thanks a lot for leading today's discussion!
@all: Let me know if you have any additions or comments to the minutes.
Btw, I still have problems to edit the wiki. Would you all agree to use a shared googledoc? I am asking because of the new EU data protection laws, which led KCL to warn us against using google. As long as we do not share any personal data, however, it should be fine.
cheers,
Helvi
Call: Einstein Toolkit Working group ``Cosmology and Particles'', 25 June 2018
Participants:
Katy Clough, Isabel Cordero, Michele Grasso, Bishop Mongwane, Daniele Vernieri, Helvi Witek
1) Reminder: EU Einstein Toolkit and school in Lisbon, September 2018
- Website:
https://centra.tecnico.ulisboa.pt/network/grit/einsteintoolkit2018/ - Deadlines: 1 July 2018 (abstract submission); 15 July 2018 (registration)
2) Summer calls:
- maybe have a call in July; NO call in August;.
- next regular working group call: September 2018
3) Discussion: Bishop Mongwane on 3+1 formulation and hyperbolicity of f(R) theories
- based on papers:.
https://arxiv.org/abs/1610.07224 https://arxiv.org/abs/1707.05757 - motivation
- f(R) gravity captures class of interesting cosmological models
- e.g. Starobinsky model of inflation
- under certain conditions equivalent to scalar-tensor theories ($f'(R) \sim \phi$)
- achievements
- derive time evolution formulation for f(R) gravity, specifically ADM and BSSNOK formulation
- neat trick: use the 4-dimensional Ricci scalar $^{(4)}R$ and its time derivative $\psi=\p_{t} ^{(4)}R$ as
independent variables
- showed strong-hyperbolicity for BSSN-type formulation
- numerical tests still problematic, maybe future work
- Comments
- BSSN only valid for $\det\tilde{\gamma}=1$; maybe reference metric formulation for spherically symmetric spacetimes
- numerical issues related to gauge choice?
- future numerical tests (a la ``apples with apples'') of non-trivial cosmological or black hole spacetimes
- references for non-trivial or cosmological boundary conditions:
-
https://arxiv.org/abs/1409.3476 -
https://arxiv.org/abs/1509.08354 -
https://arxiv.org/abs/1204.2019 - general discussion on constraint evolution vs free evolution in future working group call (Isa)