Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session T11: Quantum Aspects of Black Holes and de Sitter Space |
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Sponsoring Units: DGRAV Chair: Jorge Pullin, Louisiana State University Room: Sheraton Governor's Square 17 |
Monday, April 15, 2019 3:30PM - 3:42PM |
T11.00001: Quantum gravity and black hole spin in gravitational wave observations: a test of the Bekenstein-Hawking entropy Hal M Haggard, Eugenio Bianchi, Anuradha Gupta, Bangalore S Sathyaprakash Black hole entropy is a robust prediction of quantum gravity with no observational test to date. We use the Bekenstein-Hawking entropy formula to determine the probability distribution of the spin of black holes at equilibrium in the microcanonical ensemble. We argue that this ensemble is relevant for black holes formed in the early universe and predicts the existence of a population of black holes with zero spin. Observations of such a population at LIGO, Virgo, and future gravitational wave observatories would provide the first experimental test of the statistical nature of black hole entropy. |
Monday, April 15, 2019 3:42PM - 3:54PM |
T11.00002: Quantum strong energy inequality and the Hawking singularity theorem Eleni-Alexandra Kontou, Christopher Fewster Hawking's singularity theorem concerns matter obeying the strong energy condition (SEC), which means that all observers experience a nonnegative effective energy density (EED), thereby guaranteeing the timelike convergence property. However, some classical and all quantum fields, violate the SEC. Therefore there is a need to develop theorems with weaker restrictions, namely energy conditions averaged over an entire geodesic and quantum inequalities, weighted local averages of energy densities. We have derived lower bounds of the EED in the presence of both classical and quantum scalar fields. In the quantum case these bounds take the form of a set of state-dependent quantum energy inequalities valid for the class of Hadamard states. Finally, we discuss how these lower bounds are applied to prove Hawking-type singularity theorems asserting that, along with sufficient initial contraction at a compact Cauchy surface, the spacetime is future timelike geodesically incomplete. The talk is based on: arXiv:1809.05047 and a manuscript in preparation. |
Monday, April 15, 2019 3:54PM - 4:06PM |
T11.00003: Quantum extension of Kruskal black holes Javier Olmedo, Abhay Ashtekar, Parampreet Singh In this talk, we will present a new effective quantum description for macroscopic Kruskal spacetimes, where the singularities in the `interior' region are naturally resolved. The Kruskal extension of these quantum space-times has the following features: (i) Curvature scalars remain bounded throughout the space-time; (ii) All asymptotic regions of the extension of macroscopic black holes have the same ADM mass; (iii) At low curvatures, quantum effects are negligible. The proposal is free from all known drawbacks of previous attempts to resolve the central singularity and opens a new avenue to study black hole evaporation. |
Monday, April 15, 2019 4:06PM - 4:18PM |
T11.00004: Modified commutation relationships from the Berry-Keating program Erick Aiken, Michael Bishop, Douglas Alexander Singleton Current approaches to quantum gravity suggest there should be a modification of the standard quantum mechanical commutator, $[{\hat x} , {\hat p}] = i \hbar$. Typical modifications are phenomenological and designed to result in a minimal length scale. As a motivating principle for the modification of the position and momentum commutator, we assume the validity of a version of the Bender-Brody-M\"uller variant of the Berry-Keating approach to the Riemann hypothesis. We arrive at a family of modified position and momentum operators, and their associated modified commutator, which lead to a minimal length scale. Additionally, this larger family generalizes the Bender-Brody-M\"uller approach to the Riemann hypothesis. |
Monday, April 15, 2019 4:18PM - 4:30PM |
T11.00005: Next to leading order late time behavior for black hole evaporation Paul R Anderson, Raymond D Clark, Alessandro Fabbri, Michael R. R. Good It is well known that the near horizon approximation for the modes of a quantum field gives the leading order late time behavior for black hole evaporation which is a thermal distribution at the black hole temperature. It is shown that the next to leading order contribution from the near horizon approximation does not give the true next to leading order contribution to the Hawking radiation in the case of a black hole that forms from the collapse of a spherically symmetric null shell. Instead, the true next to leading order contribution in both two and four dimensions is nonlocal and is damped much more slowly in time than the next to leading order contribution from the near horizon approximation. |
Monday, April 15, 2019 4:30PM - 4:42PM |
T11.00006: Understanding the quantum singularity structure of Kerr spacetime Deborah A Konkowski, Drew Michael Weninger The well-known naked ring singularity in the overspinning Kerr spacetime is a timelike scalar curvature singularity. We expand upon the work by Gurtug and Halilsoy on the possible resolution of this singularity using quantum theory. Just as classical singularities are indicated by geodesic incompleteness, quantum singularities are indicated by ill-posed quantum wave propagation. We analyze the naked Kerr singularity by studying s-waves impinging on it in the equatorial plane and use a Weyl limit point - limit circle analysis to determine the essential self-adjointness of the spatial portion of a relativistic Klein-Gordon operator. As we verify the Gurtug-Halisoy analysis, we discuss the possible extensions and further uses of such quantum probes. |
Monday, April 15, 2019 4:42PM - 4:54PM |
T11.00007: Thermodynamic Stability of Causal Diamonds Batoul Banihashemi, Ted Jacobson It has been shown that causal diamonds can be viewed as local gravitational thermodynamic systems. In particular, they obey a first law, and interestingly have negative temperature. The equilibrium state of the diamond is a state in which the geometry is maximally symmetric and the quantum fields are at their vacuum state. The total entropy of such a state is extremal. Second order variations of entropy and also the diamond’s free energy is considered in this work, in order to find whether the equilibrium state is stable. The answer seems to be affirmative. |
Monday, April 15, 2019 4:54PM - 5:06PM |
T11.00008: A radical proposal for the cosmological constant problem Steven J Carlip If our universe has a large cosmological constant, would we necessarily know? The obvious answer depends on an assumption of homogeneity, which may fail at the Planck scale if Λ comes from quantum fluctuations. I show that a large set of initial data describe a universe with small average expansion even with an enormous cosmological constant. Questions about time evolution remain, but it is possible that a large Λ can produce Planck scale "spacetime foam" while remaining hidden macroscopically. |
Monday, April 15, 2019 5:06PM - 5:18PM |
T11.00009: The Decay of the de Sitter Vacuum Emil Mottola Cosmological vacuum energy does not remain constant for the same reason that a uniform electric field cannot persist indefinitely in the presence of quantum fluctuations. The decay rate of the Bunch-Davies state of QFT in de Sitter space due to particle creation is calculated in real time by the same method as that for an electric field, giving Schwinger’s result. In both the electric field and de Sitter cases the particles created are verified to be real, in that they persist in the final asymptotic region if the background field is switched off. The energy density of the particles decreases the vacuum energy and the Hubble expansion rate. |
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