In my first postdoc at Utah (with Richard Price) I switched to classical general relativity and the physics of collapse and black holes. Inspired by Matt Choptuik, I started to work on the theory of critical phenomena in gravitational collapse, and continued with this topic during my second postdoc in Madrid. There I also started working with Jose Maria Martin-Garcia, who has been my main collaborator, and is now at Wolfram.

In my third postdoc at AEI (with Juergen Ehlers and Ed Seidel) I focused on numerical relativity and in particular the binary black hole problem.

From my fourth and last postdoc at Chicago (with Bob Wald), and throughout my current faculty position at Southampton, I have been dividing my time between

with side interests in matter in general relativity and gravity in 2+1 dimensions.I have published 64 refereed papers with 2700 citations. My h-number is 24. (Both excluding self-citations).

- Critical phenomena in rotating fluid collapse (with Thomas Baumgarte)
- Critical phenomena in axisymmetric electrovacuum collapse (with Thomas Baumgarte and David Hilditch)
- Critical phenomena in axisymmetric vacuum collapse (with David Hilditch and Thomas Baumgarte)
- Perfect fluid critical collapse in 2+1 spacetim dimensions (with Patrick Bourg)
- The two-body problem in 2+1 spacetime dimensions (with Jorma Louko and Adrien Loty)

- Static spherically symmetric solutions of the massless Einstein-Vlasov system and their linear perturbations
- Relativistic elasticity (with Ian Hawke and Stephanie Ericksson)
- Critical phenomena in gravitational collapse
- High-precision calculation of the critical solution and the critical exponent (with Jose Maria Martin-Garcia)
- Perturbative approach to non-spherical critical collapse the and cosmic censorship conjecture (with Jose Maria Martin-Garcia)
- Perturbative approach to charge and angular momentum scaling in critical collapse (with Jose Maria Martin-Garcia and David Garfinkle)
- Kinematics of self-similar spacetimes (with Jose Maria Martin-Garcia)
- Black hole mergers in the extreme mass ratio limit (with Leor Barack)
- Rotating collapse with large angular momentum (with Thomas Baumgarte)
- Scalar field critical collapse in 2+1 dimensions (with David Garfinkle and Joanna Jalmuzna)

- Perturbative approach to gravitational collapse (with Jose Maria Martin-Garcia)
- Numerical relativity
- Formulations of the Einstein equations, boundary conditions, and gauge choices for numerical relativity (with Jose Maria Martin-Garcia and David Garfinkle)
- finite differencing techniques for numerical relativity (with Gioel Calabrese, Jose Maria Martin-Garcia and David Garfinkle)
- apparent horizon finder
- framework for exact solution testbeds
- causal differencing (with Paul Walker)
- classification of good gauge conditions (with David Garfinkle)

- Late time generic behaviour in gravitational collapse (with Richard Price and Jorge Pullin)
- Scalar-tensor theories of gravity (with Gary Gibbons and Thibault Damour)
- Primordial density fluctuations in inflation (with Nathalie Deruelle and others)
- Perturbations in quantum cosmology
- Fluid mechanics at stellar surfaces (with Colin Please, Randy Leveque and Jeremiah Murphy)
- Magnetic stellar equilibria (with Oliver Robertshaw)

- Supervision of EPSRC postdoc Jose Maria Martin-Garcia (2002-2002), Marie Curie postdoc Gioel Calabrese (2003-2005), PPARC/STFC postdocs Ian Hawke(2004-2005), Motoyuki Saijo (2006-2008), Wynn Ho (2008-2010)
- PhD supervisor of Ian Hinder (2003-2005), David Hilditch (2004-2007), Oliver Robertshaw (2006-2010), Stephanie Erickson (2010-2014), Patrick Bourg (2018-2021)
- MPhil supervisor of Chris Nunn(2004-2006)
- PhD adviser of Uli Sperhake (2000-03), Paolo Matteucci (2000-03), Yu Huei Wu (2002-05), Luke Ronaldson (2003-06), Nils Warburton (2009-2012), Cesar Merlin (2010), Marta Colleoni (2011)