Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session Y7: Quantum Aspects of Gravity |
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Sponsoring Units: GGR Chair: John Klauder, University of Florida Room: Hyatt Regency Jacksonville Riverfront Grand 8 |
Tuesday, April 17, 2007 1:30PM - 1:42PM |
Y7.00001: Loop quantization of spherically symmetric midi-superspaces Jorge Pullin, Rodolfo Gambini We quantize spherically symmetric vacuum space-times using a midi-superspace reduction within the Ashtekar new variables. Through a partial gauge fixing one eliminates the diffeomorphism constraint and is left with a Hamiltonian constraint that is first class. We represent it in the loop representation and complete the quantization of its dynamics using the uniform discretization approach. We discuss similarities and differences with other approaches to the dynamics of loop quantum gravity. [Preview Abstract] |
Tuesday, April 17, 2007 1:42PM - 1:54PM |
Y7.00002: Regge Calculus and the Quantum Computational Universe Warner Miller, Jonathan McDonald This talk examines the use of Regge Calculus as a tool to embed a quantum computational network into a spacetime manifold. After briefly describing Seth Lloyd's recent model Computational Universe model for spacetime histories, and introducing some basic features of Regge Calculus, we will explore the use null edges in Regge Calculus. Special attention will be focused on the coupling of the Regge equations to the computational network. In particular, we examine the right-hand side of the Regge equations and the coupling of the source in a lattice spacetime. [Preview Abstract] |
Tuesday, April 17, 2007 1:54PM - 2:06PM |
Y7.00003: The Computational Universe: Quantization of Space-time without Quantization Jonathan McDonald, Warner Miller The Computational Universe model proposed by Seth Lloyd provides a base framework for taking a discrete quantum system of interacting qubits and Regge Calculus to derive the resultant histories of spacetimes. In this framework, the spacetime is an embedding of a quantum computational network of pairwise interacting qubits in a 4-dimensional manifold. The computational network is quantum, but the spacetime is not. What might we learn about quantum gravity from a theory that identifies spacetime as the geometry resulting from interactions of a quantum system. This talk looks at the simplest model of such a computational universe; the spacetime histories that result from a single interaction of one pair of qubits. In this way, it is our hope to obtain quantum efects of the spacetime without direct quantization. The framework is applied to our simplest model and we analyze the features of the resulting geometries. [Preview Abstract] |
Tuesday, April 17, 2007 2:06PM - 2:18PM |
Y7.00004: ABSTRACT WITHDRAWN |
Tuesday, April 17, 2007 2:18PM - 2:30PM |
Y7.00005: Macroscopic Effects of the Quantum Trace Anomaly Emil Mottola, Ruslan Vaulin The low energy effective action of gravity in any even dimension generally acquires non-local terms associated with the trace anomaly, generated by the quantum fluctuations of massless fields. The local auxiliary field description of this effective action in four dimensions requires two additional scalar fields, not contained in classical general relativity, which remain relevant at macroscopic distance scales. The auxiliary scalar fields depend upon boundary conditions for their complete specification, and therefore carry global information about the geometry and macroscopic quantum state of the gravitational field. The scalar potentials also provide coordinate invariant order parameters describing the conformal behavior and divergences of the stress tensor on event horizons. [Preview Abstract] |
Tuesday, April 17, 2007 2:30PM - 2:42PM |
Y7.00006: Stress Tensor from the Trace Anomaly in Black Hole Spacetimes. Ruslan Vaulin, Paul Anderson, Emil Mottola We compute the expectation value of the quantum stress tensor for conformal matter fields from the trace anomaly, in Schwarzschild and Reisner-Nordstrom spacetimes. We show that the two scalar auxiliary fields associated with the anomaly can be adjusted to obtain finite stress tensors on the Reissner-Nordstrom event horizon, including in the extreme Q=M case. We compare this result to other analytic approximation methods which predict an infinite stress tensor on the horizon, and existing numerical results. The classical stress tensor of the auxiliary fields associated with the anomaly gives a general approximation for the renormalized quantum stress tensor in qualitative agreement with numerical evaluations in the vicinity of all Reisner-Nordstrom horizons. [Preview Abstract] |
Tuesday, April 17, 2007 2:42PM - 2:54PM |
Y7.00007: Efficient computation of Lorentzian 6J symbols Joshua Willis Spin foam models are a proposal for a quantum theory of gravity, and an important open question is whether they reproduce classical general relativity in the low energy limit. One approach to tackling that problem is to simulate spin-foam models on the computer, but this is hampered by the high computational cost of evaluating the basic building block of these models, the so-called 10J symbol. For Euclidean models, Christensen and Egan have developed an efficient algorithm, but for Lorentzian models this problem remains open. In this talk we describe an efficient method developed for Lorentzian 6J symbols, and we also report on recent work in progress to use this efficient algorithm in calculating the 10J symbols that are of real interest. [Preview Abstract] |
Tuesday, April 17, 2007 2:54PM - 3:06PM |
Y7.00008: Effective Length in Extended Causal Sets Jose L. Balduz Jr. Causal sets are directed simple graphs with partial ordering. They describe spacetime at the smallest possible length and time scales, and are thought to be a suitable starting point for a theory of quantum gravity. We extend the definition of causal sets in three ways. First, we acknowledge the transitivity ambiguity, which is related to time-like geodesics and nonlocality, by explicitly identifying the local geodesic core and the nonlocal halo for any given causal set. Second, we relax the partial ordering condition by allowing causal loops. Third, we define an action or cost function, as a sum over all loops in the causal set, which highlights nonlocal links and causal loops. We then use this extended causal set scenario to calculate the effective length (distance, invariant interval) between causally related points, using a directed conductance model, wherein resistance is equivalent to distance; this measure is compared to the naive graph distance (i.e. the number of links along a geodesic connecting two points). We first consider the smallest causal sets and exact quantum states. For larger causal sets, we use an approximation in the spirit of Born-Oppenheimer, with a fixed geodesic core and a statistical distribution of nonlocal and causal loop links. [Preview Abstract] |
Tuesday, April 17, 2007 3:06PM - 3:18PM |
Y7.00009: Black Hole production in cosmic ray showers Arunava Roy, Marco Cavaglia One way around the hierarchy problem of particle physics is to introduce large extra dimensions (LED). This suggests that gravity may become strong at the TeV and so production of scale black holes (BH's) would be possible by particle colliders and UHECR's. The interesting question is, what would be the BH signatures and whether we would detect them at the LHC or at the Auger Observatory. We also deal with the case of rotating BH's and how they may decay. Page [1976] showed that the power emitted from rotating four-dimensional BH's increases with angular momentum and so it is worth considering if this picture changes in higher dimensions. Also discussed is the case of excited string excitations from the decay of strings produced by neutrino-quark interactions. Ref: Page, D.N. (1976), Particle emission rates from a black hole. II. Massless particles from a rotating hole, Phys. Rev. D 14, 3260 - 3273 [Preview Abstract] |
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