Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session S13: Quantum Gravity and Cosmology |
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Sponsoring Units: GGR Chair: Paul Andeson, Wake Forest University Room: Key 9 |
Monday, April 13, 2015 1:30PM - 1:42PM |
S13.00001: SL(2,C) Chern-Simons Theory and Quantum Gravity with a Cosmological Constant Hal Haggard, Muxin Han, Wojciech Kaminski, Aldo Riello We show a relation between 4-dimensional quantum gravity with a cosmological constant and SL(2,C) Chern-Simons theory in 3-dimensions with knotted graph defects. In particular, we study the expectation value of a non-planar Wilson graph operator in SL(2,C) Chern-Simons theory on $S^3$. We analyze its asymptotic behavior in the double-scaling limit in which both the representation labels and the Chern-Simons coupling are taken to be large, but with fixed ratio. We find that a class of flat connections in the graph complement manifold are in correspondence with the geometries of constant curvature 4-simplices. We show that the asymptotic behavior of the amplitude contains an oscillatory part proportional to the Regge action for the single 4-simplex in the presence of a cosmological constant. In particular, the cosmological term contains the full-fledged curved volume of the 4-simplex. Interestingly, the volume term stems from the asymptotics of the Chern-Simons action. Another peculiarity of our approach is that the sign of the curvature of the reconstructed geometry, and hence of the cosmological constant in the Regge action, is not fixed a priori, but rather emerges semiclassically and dynamically from the solution of the equations of motion. [Preview Abstract] |
Monday, April 13, 2015 1:42PM - 1:54PM |
S13.00002: Quantum resolution of timelike singularities in spherically symmetric, self-similar spacetimes Deborah Konkowski, Thomas Helliwell, Jon Williams A definition of quantum singularity for the case of static spacetimes has recently been extended to conformally static spacetimes. Here the theory behind quantum singularities in conformally static spacetimes is reviewed, and then applied to a class of spherically symmetric, self-similar spacetimes. We use solutions of the massless Klein-Gordon equation as test fields. In this way we find the ranges of metric parameters for which classical timelike singularities in these spacetimes are resolved quantum mechanically, in the sense that the Hamiltonian operator is essentially self-adjoint, so the evolution of quantum wave packets lacks the usual ambiguity associated with scattering off singulartities. [Preview Abstract] |
Monday, April 13, 2015 1:54PM - 2:06PM |
S13.00003: Numerical loop quantum cosmology: some recent results Parampreet Singh We will discuss some of the recent results obtained using numerical techniques in loop quantum cosmology. We focus on two models: an isotropic universe with a negative potential and the Bianchi-I vacuum spacetime. Quantum evolution with different kinds of states in these spacetimes shows the resolution of singularities and existence of quantum bounce. In the case of the negative potential, loop quantum universes undergo a cyclic evolution with relative fluctuations tightly bound in different cycles. In the case of the anisotropic model, the shear scalar is shown to be finite in the entire evolution. We also discuss the validity of the effective spacetime description for these spacetimes. [Preview Abstract] |
Monday, April 13, 2015 2:06PM - 2:18PM |
S13.00004: Phenomenology of Loop Quantum Cosmology Ivan Agullo This talk will provide an up-to-date summary of the predictions of loop quantum cosmology for the primordial spectrum of curvature perturbations. [Preview Abstract] |
Monday, April 13, 2015 2:18PM - 2:30PM |
S13.00005: Consistent quantum prediction in spin-foam quantum cosmology David Craig A complete ``consistent histories'' framework is given for a covariant ``spin-foam'' quantum cosmological model, a highly symmetry-reduced (FLRW) model of covariant loop quantum gravity. A decoherence functional is constructed through which probabilities may be consistently extracted from quantum amplitudes. Branch wave functions corresponding to different possible quantum histories of the universe are described, such as whether the universe ``bounces'' at small volume or becomes singular. We discuss the construction and calculation of such branch wave functions, with an emphasis on the crucial role played by the decoherence of histories in arriving at self-consistent quantum predictions for these closed quantum systems. [Based on joint work with Parampreet Singh] [Preview Abstract] |
Monday, April 13, 2015 2:30PM - 2:42PM |
S13.00006: Emergence of constant curvature spacetimes with an effective charge and cosmological constant in loop quantum cosmology Anton Joe, Naresh Dadhich, Parampreet Singh The loop quantum dynamics of Kantowski-Sachs and the interior of higher genus black hole spacetimes with cosmological constant has some peculiar features not shared by various other spacetimes in loop quantum cosmolgy. As in the other cases, though the quantum geometric effects resolve the singularity and result in a bounce, after the bounce a spacetime with small spacetime curvature does not emerge at late times. Instead, asymptotically the spacetime has constant spacetime curvature with a product manifold. Interestingly, though the spacetime curvature of these asymptotic spacetimes is very high, the effective metric of these spacetimes is a solution to the Einstein field equations. Analysis of the components of the Ricci tensor shows that after the singularity resolution, the Kantowski-Sachs spacetimes lead to an effective charged Nariai, and, the higher genus black hole interior lead to an anti Bertotti-Robinson spacetime with an effective tachyonic charge. The asymptotic spacetimes have an effective cosmological constant which is different in magnitude, and sometimes even its sign, from the cosmological constant in the Kantwoski-Sachs and higher genus black hole metrics. [Preview Abstract] |
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