Reality Conditions

Thursday, April 06, 2006

Report on BritGrav 6

Two days of conference. 29 talks. 2 lunches, 1 drinks reception, and 4 coffee breaks. (Actually, the afternoon coffee breaks are called "tea breaks". These British...) A brief summary of the highlights:


Day dedicated to classical General Relativity. Many talks on neutron stars, mostly about modelling which gravitational wave signatures do different processes in neutron stars leave. The talk that won the "Best student talk" prize was in this section, being by Brynmor Haskell of Southampton on the possibility of detecting "mountains" (large assymetries) in neutron stars. By the way I learnt that LIGO has reached its designed sensitivity already. Also today were some talks on conformal analysis techniques, numerical relativity (Carsten Gundlach from Southampton explained how the problem of modelling numerically black hole merging has been solved recently) and one on the Einstein-Cartan theory (gravity with torsion) as a possible explanation for inflation.

On the evening there was a drinks reception with free drinks and food :-), over the course of which I explained to Kirill Krasnov's girlfriend what blogging was about.


Day dedicated to black holes, quantum field theory in curved spacetime, and quantum gravity. More things of interest for me today, so the report is longer and more complete. All our research group gave talks.

Sam Dolan from Cambridge talked on wave scattering by a Schwarzschild black hole, considering scalar and fermion fields and results for wavelength comparable or much larger than the black hole radius. Gabor Kunstater, who is visiting our group from Winnipeg, talked about highly damped quasinormal modes of black holes, the famous "log 3" factor which may or may not signal a connection with quantum gravity, and the differences of the Reissner-Nordstrom case with the Schwarzschild one. (In RN the asymptotic behaviour for high frequency replaces the log 3 by log 5, but there is an intermediate regime where perturbations see only one horizon and there the behaviour has a log 3). Elisabeth Winstanley gave a talk with a title that at first glance could pass by a shampoo advertisement: "Abundant, stable EYM hair for black holes in AdS", in which she showed that there is no upper bound for how much "hair" an Einstein - Yang-Mills black hole in AdS can have.

Lutz Osternbrink from York derived averaged energy inequalities for the nonminimally coupled scalar field, which is atyipical in that it violates the pointwise energy conditions even at the classical level. These averaged energy conditions resemble those that apply for quantum fields in general as discussed in Chis Fewster's seminar.

Edward Anderson from Cambridge gave a talk on "The problem of time", the first transparency added below the title: " about a conceptual problem in reconciliating General Relativity and Quantum Mechanics, and not about why this talk is handwritten and monochromatic". He started by saying "let's take General Relativity seriously" and put on a transparency full of complicated-looking handwritten equations all in red, provoking widespread laughter. He discussed four possible ways of understanding the "problem of time" that the Hamiltonian of GR vanishes so in the corresponding "Schroedinger equation" there is no time evolution: 1) find a way to rewrite the equation so a "hidden time" appears; 2) the entire universe is indeed timeless, but in a semiclassical approximation an emergent time appears with respect to a background; 3) reality is truly timeless, and we must rethink the basis of dynamics to make it a theory of "being" and not of "becoming"; 4) GR is not the correct classical theory to quantize.

Now for the talks of us locals, starting with the research students. George Kottanattu talked on an axisymmetric SU(2) geon black hole solution he is constructing, with the intention of studying its thermodynamics. It is a generalization of the solution found in this paper; the study of Hawking radiation for geons was kicked off several years ago by this paper. Richard Johnson talked on mappings between spaces of functions arising from the Lorentz group, in particular the mapping of Conformal Field Theory correlation functions to Twistor space. Ileana Naish-Guzman talked about problems in the regularization of the Ponzano-Regge model for 3+0 quantum gravity, showing that the conventional regularization is ill-defined for many observables. And I talked about the particle detector model I have described here. My talk went quite well, by the way, thanks for asking. Chris Fewster was nice enough to tell me afterwards that on occasions during the talk he had thought of questions to ask, finding only that my next transparency always answered them.

Our supervisors: Jorma Louko talked about group averaging techniques for quantizing gauge systems and a particular example he has worked on with a previous research student here, Alberto Morgado. John Barrett and Kirill Krasnov both talked on 3D quantum gravity as Ilenana did; John gave a more technical talk describing the Turaev-Viro model (which unlike the Ponzano-Regge includes a cosmological constant, which is key for eluding regularization problems) and Kirill gave a more conceptual presentation on how 3D quantum gravity arises naturally from starting with Feynmann diagrams for particles and "dressing" them with extra geometrical structure, basically via making the momenta group-valued.

On the whole, a nice experience, although it is more fun when the conference is elsewhere and we get to travel. Next time that will happen for me is in July, going to the Marcel Grossmann Meeting in Berlin. Looking forward to it...


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