The reduced phase space quantization of a closed Friedmann Universe is described. Its matter content is constituted by a specific perfect fluid. It is shown that, for this particular model, specific boundary conditions can be related to the algebra of Dirac observables.
Professor Kunihito Uzawa from Kwansei Gakuin University, Japan, visited Gr@v in the last week of September 2018 and gave a seminar on "No-Go theorems for ekpyrosis from ten-dimensional supergravity". (In the photo with Eugen Radu.)
Abstract: In this talk, we present whether the new ekpyrotic scenario
can be embedded into ten-dimensional supergravity. We use that the
scalar potential obtained from flux compactifications of type II
supergravity with sources has a universal scaling with respect to the
João Rosa was interviewed for Porto Canal's "Mentes que brilham" about his work on stimulated axion decay around primordial black holes as a possible origin for fast radio bursts, recently published in Physical Review Letters. He also gave a related interview to the radio programme "Click" on Antena 1.
Watch the presentation movie of the COST Action CA16104 Gravitational waves, black holes and fundamental physics (GWverse), in which Gr@v is involved as part of the core group.
The movie was created at the University of Aveiro (Portugal), written and directed by Carlos Herdeiro, with Design and Graphics by Joana Reis and Ana Sousa and Edited by Pedro Henriques.
The article "Stimulated axion decay in superradiant clouds around astrophysical black holes" (arXiv:1709.06581), co-authored by Gr@v member João Rosa and Tom Kephart (Vanderbilt University, USA), has been accepted for publication in Physical Review Letters and will be highlighted as one of the PRL Editors' Suggestions (a distinction attributed to about one in six Letters).
The black hole theorist and cosmologist Stephen Hawking passed away at the age of 76. Stephen Hawking distinguished himself not only as a brilliant scientist, with remarkable contributions such as the discovery of black hole evaporation, but also as an active science communicator with best selling books, most notably A brief history of time.
One well known problem of the standard cosmological constant model is the tension between the high level of clustering observed in the CMB and the one obtained from large-scale structures. This may be an indication that the way dark energy affects clustering might differ from a simple cosmological constant.
