Quantum Gravity Colloquium 6

5 Oct 2011, 09:00 → 7 Oct 2011, 18:30 Europe/Zurich

Lecture Hall F (FAU Erlangen-Nürnberg)

Alexander Stottmeister (FAU Erlangen-Nürnberg), Andreas Thurn (FAU Erlangen-Nürnberg), Antonia Zipfel (FAU Erlangen-Nürnberg), Norbert Bodendorfer (FAU Erlangen-Nürnberg), Suzanne Lanéry (FAU Erlangen-Nürnberg)

The meeting is intended for PhD students and first year post-Docs working on Quantum Gravity and related topics across Europe. It shall provide an intense atmosphere of discussion and exchange among upcoming researchers, hopefully extending existing or leading to new collaborations among people from possibly different areas. The meeting is funded by the ESF programme "Quantum Geometry and Quantum Gravity": 

The European Science Foundation (ESF) provides a platform for its Member Organisations to advance science and explore new directions for research at the European level. Established in 1974 as an independent non-governmental organisation, the ESF currently serves 78 Member Organisations across 30 countries.

Map From_erlangen_mainstation_to_AB_Hotel.pdf From_erlangen_mainstation_to_AB_Hotel_with_bus.pdf

Wednesday 5 October

1 Opening

2 Kristina Giesel: Canonical Dynamics: From Classical to Quantum

10:15 Coffee Break

3 Andreas Thurn: An Invitation to the New Variables, with Possible Applications

Slides QGC6_-_An_Invitation_to_the_New_Variables.pdf

4 Norbert Bodendorfer: Possible Applications of Loop Quantum Supergravity

12:30 Lunch Break

5 Jakub Mielczarek: Quantum dynamics of the reduced phase space loop cosmology

In standard loop quantum cosmology (LQC) one applies the Dirac quantisation method, which postpones solution of the Hamiltonian constraints to the quantum level. In the alternative approach, called the reduced phase space (RPS) quantisation, one solves constraints already at the classical level and quantisation is carried out on the physical phase space. In this talk, we present reduced phase space quantisation of the loop cosmology with a free scalar field. We define physical Hamiltonian for this model which is proven to be essentially self-adjoint. Subsequently, the time is introduced by virtue of the Stone's theorem. Based on this, we study evolution of the coherent quantum states in this framework. We investigate fluctuations of the quantum variables in the resulting bouncing universe. Finally, we address the issue so-called cosmic recall and cosmic amnesia in the framework of RPS LQC.

Slides Mielczarek_QGC6.pdf

6 Torsten Schönfeld: Gauge fixing and dynamical r-matrices in 2+1 gravity

We construct the gauge-invariant phase space of 2+1-dimensional gravity via Dirac's gauge fixing procedure. We describe the resulting Dirac bracket and show that it is related to dynamical r-matrices.

15:30 Coffee Break

7 Remigiusz Durka: Gravitational Noether charges and Immirzi parameter

It has been shown that the mass, angular momentum and entropy can be obtained from the gravitational diffeomorphic Noether charges. Now the constrained topological BF theory with anti-de Sitter gauge group allows to extend this approach to the case of the first order gravity with a negative cosmological constant, the Holst modification and topological invariants (Nieh-Yan, Euler, and Pontryagin). Topological terms contribute to the boundary terms in the regularization scheme for asymptotically AdS spacetimes in a way that differentiability of the action is automatically secured. Intriguingly, derived thermodynamics does not depend on the Immirzi parameter for the AdS-Schwarzschild and AdS-Kerr cases.

Slides Durka-Erlangen.pdf

8 Michał Szcząchor: The symmetric consistent matter field coupling to Holst action with full set of topological term

"Symmetries can preserve some physical properties". In the talk it will be emphasized how the symmetries of the theory can prevent physical properties which one can expected. In particular the Holst action with enlarged symmetries as well as a matter coupling will be discussed. The MacDowell-Mansuri construction will be used as a nice mathematical method to add extra symmetries like supersymmetry or Maxwell-AdS symmetry. By this construction the gravitino field or constant electromagnetic filed will be introduced. Also an another matter fields will be added to Holst action. It will be shown that as a consequences of use the supersymmetry, the Immirzi parameter does not occur in classical dynamics.

Thursday 6 October

9 Frank Hellmann - Spin foams, state sums, etc.

10:45 Coffee Break

10 Mingyi Zhang: Asymptotics of spin foam amplitude on simplicial manifold

I will show the recent work on the asymptotic behavior of spin foam amplitude on simplicial manifold, which are done with Muxin Han. We show that for a critical configuration, we can classify the solution in to different types both in Euclidean and Lorentz model. Therefore the Regge action reproduced here can be viewed as a discretized Palatini action with on-shell connection. The asymptotic formula of the spin foam amplitude is given by a sum of the amplitudes evaluated at all possible critical congurations, which are the products of the amplitudes associated to dierent type of geometries

11 Wolfgang Wieland: Twistorial phase space for complex Ashtekar variables

We generalise the SU(2) spinor framework of twisted geometries developed by Dupuis, Freidel, Livine, Speziale and Tambornino to the Lorentzian case, that is the group SL(2,C). We show that the phase space for complex valued Ashtekar variables on a spinnetwork graph can be decomposed in terms of twistorial variables. To every link there are two twistors---one to each boundary point---attached. The formalism provides a new derivation of the solution space of the simplicity constraints of loop quantum gravity. Key properties of the EPRL spinfoam model are perfectly recovered.

Slides Erlangen.pdf

12:45 Lunch Break

12 Antonia Zipfel: Solving the Euclidean Scalar Constraints by Spin-Foam Methods

It is often emphasized that spin-foam models could realize a projection on the physical Hilbert space of canonical Loop Quantum Gravity in the spirit of a rigging map construction. If this is indeed the case then the constraints have to vanish in the physical scalar product defined through spin-foams. We analyze the one-vertex expansion of a simple Euclidean spin-foam and find that it annihilates the Euclidean Hamiltonian constraint of canonical Loop Quantum Gravity in 4d. However, the states constructed are special and closely related to BF-theory.

Slides QGC_8_10_11.pdf

13 Sebastian Steinhaus: Perfect discretization of path integrals

In order to define a well-defined path integral, a discretization has to be employed. However, this discretization breaks the symmetry of the continuous system in general, e.g. diffeomorphism symmetry in GR. In this context, we discuss the parametrized (an)harmonic oscillator and show how to reobtain the contiuous symmetry in the discretized path integral. Furthermore the relation between discretization independence and reparametrization invariance is discussed. In the second part of the talk, we will demonstrate that requirering invariance under Pachner moves in Regge calculus defines an invariant amplitude for the (linearized) Regge gravity path integral.

15:45 Coffee Break

14 Sean Gryb: Shape dynamics: the conformal backbone of general relativity

Shape dynamics is an equivalent description of general relativity that is, itself, free of the local problem of time. Its discovery was motivated by Julian Barbour's relational program based on a precise interpretation of Mach's writings. The key features of shape dynamics that distinguish it from general relativity are: 1) that all local symmetries, which include local Weyl invariance of the spatial metric, are linear in the momenta and can be formally solved in any dimension, and 2) that the dynamics is generated by a single global Hamiltonian constraint. We will give a summary of the key features of shape dynamics and discuss some interesting future research directions including the possibility of quantizing and a promising link to gauge/gravity dualities.

Slides utrecht_talk_oct11.pdf

15 Eckhard Strobel: Gleason's theorem

16 Social Dinner

Friday 7 October

17 Gandalf Lechner: Algebraic Quantum Field Theory: From structural analysis to the construction of models

10:45 Coffee Break

18 Alexander Stottmeister: Local Temperature in Curved Spacetime

19 Ralf Banisch: The Unruh Effect and the General Boundary Formulation of Quantum Field Theories.

A quantum field theory can be fully described by giving the amplitudes for all field configurations on the boundary of some spacetime region. Conventionally, one chooses a region bounded by an initial time slice and a final time slice, but with the General Boundary Formulation of Quantum Field Theories, arbitrary boundary geometries can be considered. I will review this approach and then ask wether or not the Unruh effect is reproduced within it. Since the Unruh effect is a fairly subtle Quantum Field Theory effect, this question will serve well to test the GBF approach. We will see that to answer this question, a vacuum state, or equivalently, a complex structure, must be specified. I will show a natural proposal by Ashtekar and Magnon for a complex structure and show indications that this is distiguished by the Unruh effect.

Slides talk_erlangen.pdf

12:45 Lunch Break

20 Tomasz Trzésniewski: The Discrete Semiclassical Action of CDT

CDT model is a nonperturbative approach to quantum gravity, demonstrating a spontaneous generation of the semiclassical solu- tion. Gravitational path integral is approximated by the weighted sum over causality-preserving simplicial manifolds i.e. causal tri- angulations. Analysis of the data from numerical Monte-Carlo simulations of CDT in 3+1 dimensions shows that behaviour of (4, 1) simplicial building blocks of spacetime can be very well de- scribed by an expansion of the classical minisuperspace model. The precise form of the discrete analogue of the minisuperspace action will be discussed. Furthermore, it will be presented that the remaining (3,2) simplices may also be successfully included in the semiclassical description, leading to the extended discrete action and that the consistency between the two frameworks exists.

Slides The_Discrete_Semiclassical_Action_of_CDT.pdf

21 Michel Buck: A unique ground state from causal structure

15:45 Coffee Break

22 Discussion