Quantum Gravity, Horizons, and Beyond

University Of Maryland, College Park, College Park MD

Investigators

Abstract

The grant will support research projects on several aspects of gravitational physics where curved spacetime plays a key role. One group of topics pertains to the outstanding fundamental problem of understanding the quantum nature of spacetime. Specifically, research will be carried out pursuant to the nature of quantum states of spacetime. Much of this work focuses on the peculiar role of event horizons, since that is thought to be a promising window on the mysteries of quantum gravity. Other work will be directed at probing the validity of Einstein's theory of gravity by exploring the theoretical and observational consequences of certain modifications of that theory, particularly as that affects the behavior of black holes. A different component of the research will address questions about the behavior of magnetized plasma around astrophysical bodies like neutron stars and black holes, taking into account the effects of curved spacetime. This work could contribute to a better understanding of observations of these objects and their surroundings made with radio telescopes. Finally, in collaboration with an experimental atomic quantum fluid research group, research will be directed at exploring and exploiting the analogy between physics of quantum fluids and fields in curved spacetime, such as in the expanding universe. The results of the proposed research will be disseminated through written articles, as well as seminars, conference talks, and colloquia, and will contribute to our understanding of fundamental questions, as well as to observations and experiments in a more interdisciplinary fashion. The PI will provide instruction and mentoring to graduate and undergraduate students, regarding scientific research, writing, and verbal communication. The PI will design and implement instruction in a University of Maryland summer programs for rising 9th graders and for high school girls interested in physics. All of these activities will contribute to technical training and scientific literacy, as well as understanding and appreciation of the insights of physics. The main areas of work concern: 1) path integral methods for computing horizon entropy in quantum gravity ensembles, 2) non-perturbative reduced phase space quantization of a compact domain in 2+1-dimensional gravity, 3) the origin of outgoing black hole modes, 4) analog quantum field theory in a Bose-Einstein condensate, 5) general relativistic treatment of magnetic helicity around black holes and neutron stars, and 6) black hole horizons in Lorentz-violating gravity theories. Under 1), one project will study the relation between the nonperturbative path integral approach and the recent semiclassical analysis using algebraic quantum field theory, and another will interrogate the role of the near-horizon imaginary time evolution method in computing horizon entropy with an otherwise real spacetime path integral. Under 2) the aim is to further understand the operators and states in the algebraic quantization found previously, including their implications for entropy and Hamiltonian (time evolution). One approach to this will be to determine the relation to the alternative, covariant phase space approach, and to the so-called corner symmetry algebra, on which much work has been done by others. Further, we may extend the treatment to allow for conical singularities, handles, or a black hole in the spatial domain. Under 3) an attempt will be made to improve understanding of the relation between gravitational anomalies and Hawking radiation, and its connection to the puzzle of the origin of the outgoing black hole modes. Additionally, an attempt will be made to use perturbative quantum gravity to characterize the expected quenching of correlations between points, one of which is near a horizon. Projects under 4) will design and interpret analog quantum field theory measurements of the quantized phonon field, working together with the Maryland Bose-Einstein condensate group. Projects under 5) will formulate the general relativistic theory of energy minimization at fixed magnetic helicity in ideal plasmas, as well as of relative helicity in domains like black holes and neutron stars with boundaries allowing for helicity injection. Projects under 6) will probe the nature of black hole horizons with non-stationary horizon generators, to better understand how the horizon structure and the possibility of its curvature singularities in the infinite past or future. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.