Cosmoparticle-wg March 2018

cosmoparticle-wg@lists.einsteintoolkit.org

2 participants
4 discussions

ET "Cosmology and particles" meeting minutes 19 March 2018
by helvi witek 19 Mar '18

19 Mar '18

Dear all, please find the minutes for today's meeting below and on our wiki: https://docs.einsteintoolkit.org/et-docs/Cosmology_and_Particles @Katy: thanks for taking them! We decided to have a call once a month on a Monday around 4:30pm (GMT), i.e., after the regular Einstein Toolkit call. The next call takes place on 23rd April 2018 where Katy will give us an introduction to GRChombo (see http://www.grchombo.org/ ) which is now publicly available. cheers, Helvi ----- Minutes Participants: Sante Carloni, Katy Clough, Michele Grasso, Bishop Mongwane, Erik Schnetter, Daniele Vernieri, Helvi Witek - Timing for regular meeting - - Agreed that we will aim to meet once a month on Mondays at 4.30pm GMT / 5.30pm CET time - Agreed that having a 20 minute discussion on a specific topic at each call is a good idea to give a focus to the call - Next meeting will be on 23rd April, with 20 minute discussion on GRChombo numerical relativity code - Horndeski theories - DV gave an introduction to Horndeski theories, which are the most general theories with an additional scalar field leading to second order field equations. - The original Horndeski paper was published in 1973 but the theory was rediscovered in 2010 in the the equivalent context of Galileons, after which it became more popular in research - The field equations can be simplified (a little!) by writing them in terms of 4 arbitrary functions of the field phi and the kinetic term X. - Covers a number of common modified gravity theories - f(R), Brans-Dicke, Gauss-Bonnet. - Recent measurements of GWs have been used to show (PRL 119 251302, 2017) that, given that the speed of propagation of GWs is c (to very high precision), several terms in the most general action must be set to zero. This may rule out the Vainstein screening mechanism. - Some work is being done to investigate the well-posedness of the equations, (see https://arxiv.org/abs/1710.10155, https://arxiv.org/pdf/1705.04370.pdf), which is crucial for their numerical formulation and evolution, but so far they have only been shown to be weakly hyperbolic. This may, however, be due to issues around gauge choices. =========================================== Dr. Helvi Witek Royal Society University Research Fellow Theoretical Particle Physics and Cosmology Department of Physics King's College London ===========================================

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ET "Cosmology and particles" meeting reminder
by helvi witek 18 Mar '18

18 Mar '18

Dear all, just a reminder for our working group call tomorrow, 19th March 2018, at 4:30pm (UTC, i.e. UK/Portugal) / 5:30pm (CET). Please consider joining via the google hangout: https://hangouts.google.com/hangouts/_/tce4j4gzcfcormnadoauiqcvg4e Daniele Vernieri kindly agreed to give us a brief introduction on Horndeski theories, the most general scalar-tensor theories yielding second order field equations that are particularly popular in cosmology. If you have any suggestions for topics, please add them to the meeting agenda: https://docs.einsteintoolkit.org/et-docs/Cosmology_and_Particles cheers, Helvi =========================================== Dr. Helvi Witek Royal Society University Research Fellow Theoretical Particle Physics and Cosmology Department of Physics King's College London ===========================================

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ET working group call
by helvi witek 12 Mar '18

12 Mar '18

Dear all, let us pick up our previous discussion in a next working group call. I would suggest next week or the week after, and created a new doodle poll to identify the most convenient times. Please fill it in until the end of the week: https://doodle.com/poll/7qdvevduu2k6ezac If you have any suggestions for topics, please add them to the meeting agenda: https://docs.einsteintoolkit.org/et-docs/Cosmology_and_Particles Daniele Vernieri kindly agreed to give us a brief introduction on Horndeski theories, the most general scalar-tensor theories yielding second order field equations that are particularly popular in cosmology. Best wishes, Helvi =========================================== Dr. Helvi Witek Royal Society University Research Fellow Theoretical Particle Physics and Cosmology Department of Physics King's College London ===========================================

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DE as GR+structure; inhomogeneous cosmology postdoc with deadline 2018-04-06
by Boud Roukema 07 Mar '18

07 Mar '18

hi all, For people who don't know me, Elo and I and some other colleagues organised a small workshop in Torun in July 2017 on the cosmology side of GR, with one of the hot questions being whether or not dark energy is just a misinterpretation of forcing an oversimplified (FLRW) family of metrics onto cosmological observations: http://cosmo.torun.pl/cosmotorun17_prog.html We are still far from consensus in answering this question - and ET is likely to play a major role. I haven't (yet) used ET non-trivially yet, although it's high on my priority list. As I presently understand it, the questions of what is Newtonian vs what is GR vs what is a numerically and analytically reliable calculation are presently a lot less-well resolved than published-paper abstracts often claim. My group's results (all software is free-licensed, see my pdf in the workshop proceedings above and follow the links) favour a quite easy production of the "extra" 16% expansion (scale factor) required at the present epoch to match observations (with an LCDM proxy), by taking structure formation into account. The relevant length scale is close to the standard extragalactic non-linear scale, a few Mpc, established observationally since the 1980s. Apologies if the following is off-topic, but we have an inhomogeneous cosmology postdoc position available here at Nicolaus Copernicus University with an application deadline of 6 April 2018: https://euraxess.ec.europa.eu/jobs/278463 Cheers Boud

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Cosmoparticle-wg March 2018