Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session K16: Quantum Aspects of Gravitation II |
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Chair: Parampret Singh, Lousiana State University Room: 104 |
Sunday, April 6, 2014 1:30PM - 1:42PM |
K16.00001: The Instability of Global de Sitter Space to Particle Creation Emil Mottola, Paul Anderson Global de Sitter space is unstable to particle creation, even for a massive free field theory with no self-interactions. The O(4,1) de Sitter invariant state is a definite phase coherent superposition of particle and anti-particle solutions in both the asymptotic past and future, and therefore is not a true vacuum state. In the closely analogous case of particle creation by a constant, uniform electric field, a time symmetric state analogous to de Sitter invariant one also exists, which is also not a particle vacuum state. The particle creation process, the mean particle number, and quantities such as energy-momentum tensor of the created particles can all be studied in real time. The energy-momentum tensor in the initial adiabatic vacuum state in de Sitter space in global S$^3$ sections is computed and shows that particle creation in the contracting phase results in an exponentially large energy density at later times, necessitating an inclusion of their backreaction effects, and leading to large deviation of the spacetime from global de Sitter space before the expanding phase can begin. The instability has consequences for cosmology and the problem of quantum vacuum energy in gravity. [Preview Abstract] |
Sunday, April 6, 2014 1:42PM - 1:54PM |
K16.00002: Resummed Quantum Gravity Prediction for the Cosmological Constant and Constraints on SUSY GUTS B.F.L. Ward We use our resummed quantum gravity approach to Einstein's general theory of relativity in the context of the Planck scale cosmology formulation of Bonanno and Reuter to estimate the value of the cosmological constant as $\rho_{\Lambda} = $(0.0024 ev)$^4$. We show that the closeness of this estimate to experiment constrains susy GUT models. [Preview Abstract] |
Sunday, April 6, 2014 1:54PM - 2:06PM |
K16.00003: Lorentzian de Sitter Space From Causal Dynamical Triangulations Jonah Miller, Joshua Cooperman, Kyle Lee Causal Dynamical Triangulations (CDT) is a sum-over-histories approach to quantum gravity where the histories in question are treated as discrete ``causal'' piecewise flat manifolds. CDT is usually studied by running Monte Carlo simulations after analytically continuing the manifolds into Euclidean signature, so most previous investigations found that the large length-scale limit of the CDT universe's ground state is Euclidean de Sitter space. However, by fixing the geometries of the initial and final spacelike boundaries in (2+1)-dimensional CDT, we construct ensembles of triangulations where the large-scale limit of the dominant contribution to the path integral appears to be Lorentzian de Sitter space. In the context of the minisuperspace model, we confirm that, although the topological signature is Euclidean, both the spatial volume as a function of Euclidean time and the propagator for the fluctuations of the geometry as a function of Euclidean time agree well with Lorentzian de Sitter space. Comparing the spectral dimension of this ensemble with that of Lorentzian de Sitter spacetime in Causal Set theory offers possible additional evidence of the Lorentzian nature of the ensemble. This implies that the common picture of CDT's ground state needs reexamination. [Preview Abstract] |
Sunday, April 6, 2014 2:06PM - 2:18PM |
K16.00004: Quantum fluctuations and the small scale structure of spacetime Steven Carlip Quantum fluctuations of the stress-energy tensor almost certainly cause light rays to converge very rapidly at distances a bit above the Planck scale. I will explain why this is true, and offer some wild speculations about the implications for the small scale structure of spacetime. [Preview Abstract] |
Sunday, April 6, 2014 2:18PM - 2:30PM |
K16.00005: On Resolutions of Cosmological Singularities in Higher-Spin Gravity Benjamin Burrington, Leopoldo Pando Zayas, Nicholas Rombes Gravity in three dimensions is simpler than in four, due to the lack of gravitational waves, and can be recast as a Chern-Simons theory. In this context, it is straightforward to generalize Einstein's gravity, with or without cosmological constant, by changing the gauge group. Using this, we study the resolution of certain cosmological singularities, and extend the singularity resolution scheme proposed by Krishnan and Roy. We discuss the resolution of a big-bang singularity in the case of gravity coupled to a spin-4 field realized as Chern-Simons theory with gauge group $SL(4,C)$. We show the existence of gauge transformations that do not change the holonomy of the Chern-Simons gauge potential and lead to metrics without the initial singularity. We argue that such transformations always exist in the context of gravity coupled to a spin-N field when described by Chern-Simons with gauge group $SL(N,C)$. [Preview Abstract] |
Sunday, April 6, 2014 2:30PM - 2:42PM |
K16.00006: Quantum Theory of Large Amplitude Gravitational Waves Dillon Scofield The standard development of small amplitude gravitational radiation theory is amended allowing the development of a theory of large amplitude gravitational waves. The further development of the resulting theory leads to a quantum theory of gravitation and mass-spacetime compatible with an SU(4) model of elementary particle interactions. [Preview Abstract] |
Sunday, April 6, 2014 2:42PM - 3:18PM |
K16.00007: An Effective Framework for Quantum Cosmology Invited Speaker: Martin Bojowald Canonical quantum cosmology requires extensions of traditional effective methods to deal with issues such as the problem of time and general covariance. This talk reviews such an extension and presents recent results, together with possible applications to field-theoretic models. [Preview Abstract] |
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