Stephen Green

Research Interests

I work on a variety of problems in general relativity, with links to cosmology, astrophysics and AdS/CFT. I am interested in particular in dynamical scenarios with nonlinear effects, which I have studied using both analytical approaches and numerical simulations.

My recent interest has been in understanding dynamics in asymptotically anti--de Sitter (AdS) spacetimes. This is motivated both by the AdS/CFT correspondence, as well as the highly nontrivial dynamics that have been uncovered in these settings. As an example, in 2013 it was shown that the gravitational field could become turbulent---very much like a fluid---in the vicinity of large asymptotically AdS black holes. This can be understood at a broad level as arising because gravitational radiation is confined in such scenarios---it cannot propagate away---and as a result complex nonlinear dynamics can occur.

My main line of work has specifically focused on the stability of AdS spacetime. Whereas flat spacetime has been proven to be stable, small perturbations of AdS have been shown in numerical simulations to often---but not always---collapse to a black hole through a turbulent cascade of energy (again because of the confining behavior of AdS). How and when this occurs is a key question of my research, which I have addressed through a combination of numerical and multiscale perturbative techniques.

For my PhD, I studied general relativistic effects in cosmology. I constrained possible nonlinear backreaction effects that had been suggested by others as an alternative to dark energy, and I demonstrated the effectiveness of Newtonian cosmological simulations as an approximation to general relativity.

Positions Held

• 2012 -- 2014 CITA National Postdoctoral Fellow, University of Guelph

Awards

• Nathan Sugarman Award for excellence in graduate research, Enrico Fermi Institute, University of Chicago
• Blue Apple Award for best student talk, 21st Midwest Relativity Meeting
• Harvey B. Plotnick Fellowship, University of Chicago
• Postgraduate Scholarship D, NSERC

Recent Publications

• Stephen R. Green, Stefan Hollands, Akihiro Ishibashi, and Robert M. Wald, "Superradiant instabilities of asymptotically anti-de Sitter black holes," Class. Quantum Grav. 33, 125022 (2016); arXiv: 1512.02644 [gr-qc].
• Stephen R. Green and Robert M. Wald, "A simple, heuristic derivation of our 'no backreaction' results," Class. Quantum Grav. 33, 125027 (2016); arXiv: 1601.06789 [gr-qc].
• Pablo Bosch, Stephen R. Green, Luis Lehner, "Nonlinear Evolution and Final Fate of Charged Anti-de Sitter Black Hole Superradiant Instability," Phys. Rev. Lett. 116, 141102 (2016); arXiv: 1601.01384 [gr-qc].
• Stephen R. Green, Antoine Maillard, Luis Lehner, and Steven L. Liebling, "Islands of stability and recurrence times in AdS," Phys. Rev. D92, 084001 (2015); arXiv: 1507.08261 [gr-qc].
• Venkat Balasubramanian, Alex Buchel, Stephen R. Green, Luis Lehner, and Steven L. Liebling, "Reply to Comment on 'Holographic Thermalization, Stability of Anti--de Sitter Space, and the Fermi-Pasta-Ulam Paradox'", Phys. Rev. Lett. 115, 049102 (2015); arXiv: 1506.07907 [gr-qc].
• Huan Yang, Fan Zhang, Stephen R. Green, and Luis Lehner, "Coupled Oscillator Model for Nonlinear Gravitational Perturbations," Phys. Rev. D91, 084007 (2015); arXiv: 1502.08051 [gr-qc].
• Alex Buchel, Stephen R. Green, Luis Lehner, and Steven L. Liebling, "Conserved quantities and dual turbulent cascades in Anti-de Sitter spacetime," Phys. Rev. D91, 064026 (2015); arXiv: 1412.4761 [gr-qc].
• Stephen R. Green and Robert M. Wald, "How well is our universe described by an FLRW model?," Class. Quantum Grav. 31, 234003 (2015); arXiv: 1407.8084 [gr-qc]
• Venkat Balasubramanian, Alex Buchel, Stephen R. Green, Luis Lehner, and Steven L. Liebling, "Holographic Thermalization, Stability of Anti-de Sitter Space, and the Fermi-Pasta-Ulam Paradox," Phys. Rev. Lett. 113, 071601 (2014); arXiv: 1403.6471 [hep-th].
• Stephen R. Green, Federico Carrasco, and Luis Lehner, "Holographic path to the turbulent side of gravity," Phys. Rev. X4, 011001 (2014); arXiv: 1309.7940 [hep-th].
• Stephen R. Green, Joshua S. Schiffrin, and Robert M. Wald, "Dynamic and thermodynamic stability of relativistic, perfect fluid stars," Class. Quantum Grav. 31, 035023 (2014); arXiv: 1309.0177 [gr-qc]
• Alex Buchel, Stephen R. Green, Luis Lehner, and Steven L. Liebling, Universality of non-equilibrium dynamics of CFTs from holography, arXiv: 1410.5381 [hep-th].

Seminars

• Two-timescale analysis of AdS (in)stability, Fields Institute Focus Program on 100 Years of General Relativity, Toronto, ON (2015)
• Conserved quantities and dual turbulent cascades in Anti-de Sitter spacetime, APS April Meeting, Baltimore, MD (2015)
• Holographic Themalization, Stability of AdS, and the Fermi-Pasta-Ulam Paradox, CERN-CKC TH Institute on Numerical Holography, CERN (2014)
• Holographic Themalization, Stability of AdS, and the Fermi-Pasta-Ulam Paradox, 24th Midwest Relativity Meeting, Oakland University, Auburn Hills, MI (2014)
• Holographic Themalization, Stability of AdS, and the Fermi-Pasta-Ulam Paradox, 15th Canadian Conference on General Relativity and Relativistic Astrophysics, University of Winnipeg (2014)
• Holographic Path to the Turbulent Side of Gravity, 17th Eastern Gravity Meeting, West Virginia University (2014)
• Holographic Themalization, Stability of AdS, and the Fermi-Pasta-Ulam Paradox, University of Maryland (2014)
• Islands of stability and recurrence times in AdS, 2015-08-06, PI Cosmology Group Meeting
• Is AdS Stable?, 2015-05-01, PI-CITA Day
• Holographic Themalization, Stability of AdS, and the Fermi-Pasta-Ulam Paradox, 2014-08-21, PI Cosmology Group Meeting
• PIRSA:14050038, Holographic Path to the Turbulent Side of Gravity, 2014-05-07, Compute Ontario Research Day
• PIRSA:13120066, holographic path to the turbulent side of gravity, 2013-12-12, Cosmology & Gravitation
• PIRSA:12020128, Newtonian and Relativistic Cosmologies, 2012-02-09, Strong Gravity