Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session H13: Quantum Aspects of Gravitation - II |
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Sponsoring Units: DGRAV Chair: Eugenio Bianchi, Penn State Room: A224-225 |
Sunday, April 15, 2018 10:45AM - 10:57AM |
H13.00001: The emergence of spacetime in causal set theory Steven Carlip, Samuel Loomis Causal set theory---a discrete model of spacetime in which causal structure is fundamental---has many attractive features, but one potentially fatal flaw: while it is easy to construct a causal set that approximates any given spacetime, the vast majority of causal sets look nothing like any spacetime at all. Here we show that for certain ranges of coupling constants, one large class of non-manifoldlike causal sets is exponentially suppressed in the ordinary (Lorentzian) gravitational path integral. While we cannot yet generalize this result to other classes, we have promising hints. If a generalization \emph{is} possible, it will mean that spacetimes can emerge naturally from a simple and attractive discrete setting, [Preview Abstract] |
Sunday, April 15, 2018 10:57AM - 11:09AM |
H13.00002: Singularities and black holes in causal set gravity Yu Asato The causal set theory is often considered as the simplest approach to quantum gravity, but this simplicity has made it difficult to precisely define black holes in the theory. I first show that the causal set theory is not so simple as we might think, and still admits continuum. I argue that the continuum behaves like a singularity in a certain sense, and propose the internal definition of black holes in the causal set theory based on the continuum. [Preview Abstract] |
Sunday, April 15, 2018 11:09AM - 11:21AM |
H13.00003: A Measure for Manifoldlikeness of a Causal Set Miremad Aghili, Luca Bombelli, Benjamin Pilgrim Causal Set Theory is an alternative theory for quantization of spacetime. It is based on the well known result that one can extract all the components of the metric just by knowing the volumes and structure of the light cones. In Causal set theory, volumes are measured by counting the number of points (atoms of spacetime) and light cone structure is replaced with the partial order between these set of points. A generic partially ordered set does not represent a spcetime manifold. This is a big question in the field of Causal Set Theory and is important in defining the action for the theory. This presentation provides a method to measure the manifoldlikeness of a Causal Set. [Preview Abstract] |
Sunday, April 15, 2018 11:21AM - 11:33AM |
H13.00004: Mandelstam's "Quantization of the Gravitational Field" revisited Jorge Pullin, Rodolfo Gambini, Miguel Campiglia In the 1960's Mandelstam pioneered an approach to the quantization of gauge fields and gravity based on loop-dependent Dirac observables. In the gravitational case, space-time points became an emergent entity. Although some limited success in the computation of graviton propagators was achieved, the formalism proved unwieldy, in particular making it very difficult to characterize if two curves ended in the same point. We note that the use of techniques of the group of loops, in particular the loop and connection derivative, allow to overcome these technical difficulties, opening new possibilities for the quantization of gravity. We construct a path dependent action and show it is equivalent to the Einstein--Hilbert one. [Preview Abstract] |
Sunday, April 15, 2018 11:33AM - 11:45AM |
H13.00005: Canonical quantization of symmetry reduced gravitational models: recent advances Javier Olmedo In this talk I will provide a brief summary of some recent advances in symmetry reduced gravitational systems in real connection variables and their canonical quantization. Among them, black hole spacetimes and Gowdy cosmologies are among the most interesting scenarios due to its physical relevance. I will discuss some aspects of the quantum dynamics, semiclassical sectors of these models and the way quantum fluctuations of the geometry may influence the quantum dynamics of test fields on these quantum geometries. [Preview Abstract] |
Sunday, April 15, 2018 11:45AM - 11:57AM |
H13.00006: Black Hole Evaporation in (3+1) D: From a nonthermal to a thermal spectrum Paul Anderson, Raymond Clark, Michael Good Black hole evaporation is studied in the case of a (3+1)D nonrotating black hole that forms from the collapse of a null shell. Unlike the usual treatment, numerical calculations are carried out to compute the particle production that happens both during and after the collapse. The evolution from a nonthermal spectrum at early times to a thermal one at late times will be explored. [Preview Abstract] |
Sunday, April 15, 2018 11:57AM - 12:09PM |
H13.00007: BEC Black Hole Analog with Massive Phonons Richard Dudley, Paul Anderson, Alessadro Fabbri Several features, such as peaks in correlation functions, associated with the Hawking effect have been predicted to occur in Bose Einstein condensate(BEC) black hole analogs. We investigate an effective 1+1D BEC which has a constant flow velocity and a varying speed of sound in such a way as to create an acoustic black hole. The phonons in the BEC are allowed to be excited along the direction of flow as well as the transverse direction. This transverse excitation, which has previously been largely ignored, adds a mass-like term to the mode equation for the phonons. Using a simple approximation to the mode equation we compute the two-point function for the phonons and compare to previous results. We find the expected correlation peaks and a new feature, associated with undulations. [Preview Abstract] |
Sunday, April 15, 2018 12:09PM - 12:21PM |
H13.00008: Trans-Planckian issues and Emergent Gravity: from BEC to analogue Black Holes Supratik Sarkar, A. Bhattacharyay To account for the non-local interactions in a Bose-Einstein Condensate (BEC), an addition of a minimal correction term to the standard Gross-Pitaevskii model effectively can make the healing length $\xi$ decrease more rapidly with the increase of $s$-wave scattering length ($a$). From analogue gravity perspectives, this shrinking of $\xi$ via tuning $a$ through Feshbach resonance, in principle, does make the short-wavelength (i.e. high energy) regime more accessible experimentally by pushing the Lorentz-breaking dispersion even more towards the UV side. The effects of the Lorentz-breaking quantum potential term in the BEC-dynamics on independent multiple scales can be captured through a UV-IR coupling of the phonon-excitation-modes of a massive minimally coupled Klein-Gordon field. The analysis was argued on a (3+1)D flat spacetime. The analysis is extended for a canonical acoustic black hole in a (3+1)D curved spacetime through presenting an analogue gravity model upto $\mathcal{O}(\xi^2)$ accuracy. In our formalism, the growth rate of the large-wavelength 'secondary' $\omega$ modes is found to hold the clue to extract the lost information regarding the short-wavelength 'primary' $\omega_1$ modes. This can reveal the relative abundance of the originally Hawking radiated quanta. [Preview Abstract] |
Sunday, April 15, 2018 12:21PM - 12:33PM |
H13.00009: Resolution of singularities in dynamic spacetimes Deborah Konkowski, Thomas Helliwell Preliminary work on resolving the spacelike scalar curvature singularity in the $r < 2m$ dynamic region of a Schwarzschild black hole using quantum mechanical techniques has not yet been successful. The Horowitz-Marolf criterion of essential self-adjointness that can heal timelike singularities in static and conformally static spacetimes has been extended formally to the Schwarzschild singularity and it is shown to be not essentially self-adjoint, in other words, quantum mechanically singular. In this presentation I will compare these results with recently successful attempts to use quantum field theory techniques to resolve the scalar curvature singularity in Schwarzschild as presented by Hofman and Schneider and quantum mechanical techniques to resolve the scalar curvature ring singularity in overspinning $a > m $ Kerr spacetime as presented by Gurtug and Halisoy. Comments on the relative merits of the techniques will be made. [Preview Abstract] |
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