Publications

Gravitational lensing beyond geometric optics: II. Metric independence (2019)
[arXiv] Description
This paper shows that solutions in geometric optics (and beyond) depend surprisingly little on the spacetime geometry. It amounts to identifying a broad class of symmetries in the equations for null geodesics, amplitudes, polarization states, and so on. For null geodesics and certain other objects, seven of the ten metric components are shown to be irrelevant.
It follows that i) using optical observations to infer a metric can be problematic, and ii) known solutions in one geometry can be used also in new geometries. Various examples of the latter are discussed. This includes a method to compute the highfrequency scattering of light or gravitational waves by a compact mass just by applying a transformation to a plane wave in flat spacetime.
 Persistent gravitational wave observables: General framework (2019)

Gravitational lensing beyond geometric optics: I. Formalism and observables (2019)
[arXiv] [DOI] Description
This paper focuses on how various observables and conservation laws are affected by corrections to geometric optics. Scalar, electromagnetic, and gravitational waves are all discussed.
It is shown that while a notion of "corrected propagation direction" is unambiguous in the scalar case, the concept is problematic in general for electromagnetic and gravitational waves. Rather, there are in general multiple simultaneous propagation directions which appear at finite frequency.
Different components of the electromagnetic field or Weyl tensor are shown to scale with different powers of the frequency. This is reminiscent (and related) to the peeling theorems which say that these components fall off at different rates at large distances, although the results obtained here are valid locally and do not assume anything about the asymptotic structure of the spacetime.
Senses are discussed in which knowledge of a highfrequency scalar field determines aspects of an electromagnetic field. Similarly, it is discussed how electromagnetic fields determine gravitational fields. A kind of "double copy" is shown to appear naturally.
 Foundations of the selfforce problem in arbitrary dimensions (2018)
 Selfforces in arbitrary dimensions (2017)
 Metricindependence of vacuum and forcefree electromagnetic fields (2017)
 Generating exact solutions to Einstein's equation using linearized approximations (2016)
 Selfforces on static bodies in arbitrary dimensions (2016)
 Optics in a nonlinear gravitational plane wave (2015)
 Motion in classical field theories and the foundations of the selfforce problem (2015)
 The notsononlinear nonlinearity of Einstein's equation (2014)
 Gravitational selftorque and spin precession in compact binaries (2014)
 Tails of plane wave spacetimes: Wavewave scattering in general relativity (2013)
 Magnetorotational instability in relativistic hypermassive neutron stars (2013)
 Strong lensing, plane gravitational waves and transient flashes (2013)
 Caustics and wave propagation in curved spacetimes (2012)
 Mechanics of extended masses in general relativity (2012)
 Bobbing and Kicks in Electromagnetism and Gravity (2010)
 Effective stressenergy tensors, selfforce, and broken symmetry (2010)
 A Rigorous Derivation of Electromagnetic Selfforce (2009)
 Electromagnetic selfforces and generalized Killing fields (2009)
 Electromagnetic selfforces and generalized Killing fields (2009)
 Selfforces from generalized Killing fields (2008)
 Approximate spacetime symmetries and conservation laws (2008)
 Extendedbody effects in cosmological spacetimes (2007)
 Multipole structure of current vectors in curved spacetime (2007)
 Selfforces on extended bodies in electrodynamics (2006)
 Mass loss by a scalar charge in an expanding universe (2002)