504 citations · 2.7k across the 41 of their papers we have counts for
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The Kerr/CFT energy gap
Robert Penna
Noether charges in gravity are always defined with respect to a reference metric, but the near-horizon extremal Kerr (NHEK) solution does not come with an obvious choice of referen…
Scattering amplitudes for cylindrical gravitational waves
Robert Penna
Cylindrical gravitational waves are interesting because they enjoy an infinite dimensional symmetry called Geroch symmetry. In this paper, we compute the 2-particle tree-level S-ma…
The Geroch Group in One Dimension
Robert F. Penna
We study the dimensional reduction of general relativity to a single null spacetime dimension. The dimensionally reduced theory is a theory of six scalar fields governed by three c…
A Lax Operator for Supergravity
Robert F. Penna
General relativity and supergravity become integrable systems after dimensional reduction to two spacetime dimensions. This means the equations of motion can be encoded in the flat…
Twistor Actions for Integrable Systems
Robert F. Penna
Many integrable systems can be reformulated as holomorphic vector bundles on twistor space. This is a powerful organizing principle in the theory of integrable systems. One shortco…
Near-horizon Carroll symmetry and black hole Love numbers
Robert F. Penna
According to the black hole membrane paradigm, the black hole event horizon behaves like a 2+1 dimensional fluid. The fluid has nonzero momentum density but zero velocity. As a res…