Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session T10: Focus Session: Non-Perturbative Quantum Gravity |
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Sponsoring Units: GGR Chair: Seth Major, Hamilton College Room: Marriott Tampa Waterside Room 6 |
Monday, April 18, 2005 1:30PM - 2:06PM |
T10.00001: Recent Advances in Quantum gravity Invited Speaker: This talk will review the most significant of the recent advances in loop quantum gravity. It will be addressed to non-experts. [Preview Abstract] |
Monday, April 18, 2005 2:06PM - 2:18PM |
T10.00002: Pre-classical solutions in Bianchi I loop quantum cosmology Daniel Cartin, Gaurav Khanna Loop quantum cosmology, the symmetry reduction of quantum geometry for the study of various cosmological situations, leads to a difference equation for its quantum evolution equation. To ensure that solutions of this equation act in the expected classical manner far from singularities, additional restrictions are imposed on the solution. Here we consider the range of solutions for the anisotropic Bianchi I model that meet these restrictions, and find that they are rather limited. The implications of these results for the full theory of quantum geometry will be discussed. [Preview Abstract] |
Monday, April 18, 2005 2:18PM - 2:30PM |
T10.00003: Horizon Constraints and Black Hole Entropy Steven Carlip To ask a question about a black hole in quantum gravity, one must restrict initial or boundary data to ensure that a black hole is actually present. For two-dimensional dilaton gravity, and probably a much wider class of theories, I show that the imposition of a``stretched horizon'' constraint modifies the algebra of symmetries at the horizon, inducing a central term. Standard conformal field theory techniques then fix the asymptotic density of states, reproducing the Bekenstein-Hawking entropy. The states responsible for black hole entropy can thus be viewed as ``would-be gauge'' states that become physical because the symmetries are altered. [Preview Abstract] |
Monday, April 18, 2005 2:30PM - 2:42PM |
T10.00004: Perturbation Theory in Covariant Canonical Quantization Sayandeb Basu I investigate a new idea of perturbation theory in covariant canonical quantization. This idea is motivated by computability of the ``evolving constants'' idea introduced by Rovelli---an outstanding obstacle to which has been the lack of exact general solutions in 3+1 dimensional general relativity. I present preliminary results for a toy model of a harmonic oscillator with a quartic perturbation, and show that this method reproduces the quantized spectrum of standard quantum theory. This result indicates that when the exact solutions to classical equations are not known, covariant canonical quantization via perturbation theory could be a viable approximation scheme for finding observables, and suggests a physically interesting way of extending the scope of covariant canonical quantization in quantum gravity. [Preview Abstract] |
Monday, April 18, 2005 2:42PM - 2:54PM |
T10.00005: Plugging holes in constraints on linearly Planck suppressed Lorentz violation David Mattingly, Ted Jacobson, Stefano Liberati Over the past few years much work has gone into constraining the possibility that, due to quantum gravity effects, Lorentz invariance may not be an exact symmetry of nature. A number of astrophysical phenomena, such as polarization of light from distant sources, high energy gamma rays, and the spectrum of the Crab nebula have been used to put stringent limits on Lorentz violation in particle dispersion relations that is suppressed by a single power of the Planck scale. However, despite these attempts there have been some holes in the various constraints, mainly due to the fact that this type of Lorentz violation is CPT violating. In this talk we discuss the existing holes and show that consideration of particular helicity states for threshold reactions significantly strengthens some constraints, thereby plugging these holes. We conclude that the entire parameter space of linearly suppressed Lorentz violation is bounded at a least an order of magnitude below one. [Preview Abstract] |
Monday, April 18, 2005 2:54PM - 3:06PM |
T10.00006: Causal Sets, Hypergraphs and Cosmology Jose L. Balduz Jr. Causal sets are discrete structures consisting of points and causal links; they show great promise as the starting point for quantization of spacetime and general relativity. A graph is a discrete set of nodes and connecting links. A hypergraph is a generalized graph, wherein every subset of the node set may be included as an edge, which is analogous to a (2-node) link. A fundamental correspondence is presented between causal sets and hypergraphs. This is used to define a time index for each causal set point, which well-orders the set, as well as a spatial distance between points, which obeys the triangle inequality. The complete hypergraph is considered as the prime example. The time and spatial measures provide local and global structure for the corresponding causal set, as well as a simple derivation of the Hubble Law. [Preview Abstract] |
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T10.00007: Quantum gravity with real clocks, fundamental decoherence and the black hole information puzzle Jorge Pullin We present work in collaboration with Rodolfo Gambini and Rafael Porto. Using the consistent discretization scheme we introduced, general relativity can be approximated by a constraint-free theory. This allows its quantization using the ideas of Page and Wootters, where one chooses a quantum physical variable as a clock. The resulting evolution in terms of the quantum clock is shown to be lose unitarity, even if one chooses the best possible clock. We present an estimate of such an effect, and show that it is large enough to render the black hole information puzzle unobservable: pure states would lose coherence due to this fundamental mechanism at a rate similar to the one that could be achieved by collapsing a pure state into a black hole that evaporates. [Preview Abstract] |
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