Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session Q11: Asymptotic Symmetries and QFT in Curved Spacetime |
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Sponsoring Units: DGRAV Chair: Paul Anderson, Wake Forest University Room: Sheraton Governor's Square 17 |
Monday, April 15, 2019 10:45AM - 10:57AM |
Q11.00001: The Asymptotic Behavior of Massless Fields and the Memory Effect Gautam Satishchandran, Robert M Wald We investigate the behavior of perturbations of in $d \geq 4$ Minkowski spacetime (in both even and odd dimensions) near null infinity in full, nonlinear General Relativity under the assumption that the perturbations admit a suitable expansion in $1/r$. We explicitly obtain the recursion relations on the coefficients of the $1/r$ expansion implied by the field equations (in Harmonic gauge) as well as the ``constraints''. We then consider the memory effect in fully nonlinear general relativity. We show that in even dimensions, the memory first arises at Coulombic order---i.e., order $1/r^{d-3}$---and can naturally be decomposed into ``null memory'' and ``ordinary memory.'' In odd dimensions, the memory effect vanishes near null infinity at Coulombic order and slower fall-off. The null memory is always of ``scalar type'' with regard to its behavior on spheres, but the ordinary memory can be of any (i.e., scalar, vector, or tensor) type. Scalar memory is described by a diffeomorphism, which is an asymptotic symmetry (a supertranslation) in $d=4$ and a gauge transformation for $d > 4$. Vector and tensor memory cannot be described by diffeomorphisms. |
Monday, April 15, 2019 10:57AM - 11:09AM |
Q11.00002: Horizon Foliations and Black Hole Memory Adel A Rahman, Robert M Wald We propose a notion of a "black hole memory effect" along the event horizon of a black hole spacetime, in analogy with the characterization of the memory effect at null infinity in terms of supertranslations. We define a "preferred foliation" of the event horizon during stationary eras by requiring that the expansion of the transverse null geodesics be constant. We prove existence and uniqueness of this foliation. We show that this foliation differs, in general, from another preferred foliation previously considered by Ashtekar, Beetle, and Lewandowski and provide a new characterization of the latter. We consider a black hole that is initially stationary, goes through a non-stationary era, and becomes stationary again at late times. Black hole memory is then defined in terms of the symmetry transformation of the horizon that takes one from the early time preferred foliation to the late time preferred foliation. |
Monday, April 15, 2019 11:09AM - 11:21AM |
Q11.00003: Conservation of asymptotic supermomenta from past to future null infinity Kartik Prabhu We show that asymptotic supertranslations and supermomenta on past null infinity can be matched to those on future null infinity using the Ashtekar-Hansen structure of spatial infinity. This provides an infinite number of conservation laws for nonlinear gravitational scattering in a general class of spacetimes as has been recently conjectured by Strominger. |
Monday, April 15, 2019 11:21AM - 11:33AM |
Q11.00004: The past cosmological horizon as the relevant scri minus Abhay Ashtekar, Sina Bahrami We consider gravitational radiation produced by isolated sources in spacetimes with positive cosmological constant. A suitable notion of no-incoming radiation can be imposed on the past cosmological horizon of the system by combining ideas from asymptotics and the theory of weakly isolated horizons. We introduce a notion of the total energy and angular momentum of the isolated system. This work also lays the foundations for introducing notions of future infinity where outgoing radiation can be extracted. |
Monday, April 15, 2019 11:33AM - 11:45AM |
Q11.00005: Persistent gravitational wave observables Alexander M Grant, Eanna E Flanagan, Abraham I Harte, David A Nichols The gravitational wave memory effect is the permanent relative displacement of a pair of initially comoving test particles caused by the passage of a burst of gravitational waves. Recent research has clarified the physical origin and the interpretation of this effect in terms of conserved charges at null infinity and "soft theorems". In this talk, we describe a more general class of effects, not necessarily associated with those charges and soft theorems, that are, in principle, measurable. We shall refer to these effects as persistent gravitational wave observables. Like geodesic deviation in gravitational wave memory, these observables vanish in non-radiative regions of a spacetime, and their effects "persist" after a region of spacetime which is radiating. We give three examples of such persistent observables: (i) a generalization of geodesic deviation that allows for acceleration, (ii) a holonomy observable defined in terms of a closed loop that includes the relative velocity, proper time and accumulated relative rotation effects previously identified, as well as new effects, and (iii) an observable defined using using a spinning test particle. We briefly discuss the ability of gravitational wave detectors (such as LIGO) to measure these observables. |
Monday, April 15, 2019 11:45AM - 11:57AM |
Q11.00006: Energy cost of entanglement extraction from quantum fields Lucas F Hackl, Robert H Jonsson In quantum information science, entanglement provides a valuable resource that can be used for communication, cryptography and quantum teleportation. The ground state of relativistic field theories is spatially highly entangled, so it is natural to ask if two separated parties, Alice and Bob, can extract some of this entanglement for their own use. Indeed, this can be accomplished by interacting locally with the field and thereby inevitably increasing the energy of the state. In this talk, I present lower bounds for the energy cost of entanglement extraction (measured in entropy) per mode in scalar quantum field theories and compare them to a concrete scenario where Alice and Bob are both localized in spacetime. |
Monday, April 15, 2019 11:57AM - 12:09PM |
Q11.00007: Electromagnetic Duality Anomaly in Curved Spacetimes Ivan Agullo
Maxwell's equations in the absence of sources are invariant under electric-magnetic duality transformations. This symmetry leads to a constant of motion, via Noether’s theorem, that is given by the net circular polarization of the electromagnetic field. I will describe how this symmetry remains exact also in the quantum theory in Minkowski spacetime, but not necessarily if a gravitational field is present. This implies that the polarization of photons propagating in a gravitational background can change in time, or in other words, that gravity can act as an optically active medium. This is a quantum effect, and it can be understood as the generalization of the well-known chiral anomaly of fermions to fields of spin 1. |
Monday, April 15, 2019 12:09PM - 12:21PM |
Q11.00008: Local and covariant flow relations for OPE coefficients in curved spacetime. Mark Klehfoth, Robert M. Wald Although pointwise products of quantum field observables are not well defined, products of field observables evaluated at distinct spacetime points are known to satisfy asymptotic relations called operator product expansion (OPEs) in the coincidence limit. Hollands and Wald have argued much of the key information about a quantum field theory (QFT) is contained in the coefficients of its OPEs. For interacting λφ4-theory in flat Euclidean spacetime, Holland and Hollands have derived non-perturbative "flow relations" which govern how OPE coefficients vary under changes in the interaction parameter, λ. However, serious obstacles arise if one attempts to generalize their result to curved Lorentzian spacetimes in a local and covariant manner. In this talk, I will describe these issues and sketch our resolutions for a "toy model" which is Klein-Gordon theory in curved Lorentzian spacetime with the mass parameter, m2, viewed as an interaction parameter. The strategies I describe for ensuring locality and covariance of this toy model's flow relations are expected to be applicable more generally to QFTs with nonlinear interactions in curved Lorentzian spacetimes. |
Monday, April 15, 2019 12:21PM - 12:33PM |
Q11.00009: Correlation patterns in a BEC Black Hole Analog with Massive Phonons Richard A Dudley, Paul R Anderson, Alessandro Fabbri, Roberto Balbinot Several features associated with the Hawking effect have been predicted to occur in Bose Einstein condensate(BEC) black hole analogs. An effective 1+1D BEC is investigated 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 adds a mass-like term to the mode equation for the phonons. Using a simple approximation to the mode equation the two-point function for the phonons is computed and the correlation patterns which arise due to the mass-like term are found to be significantly different from those in the massless case. |
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