My area of expertise is in theoretical cosmology and general relativity. I'm fascinated by the lumpy, inhomogeneous nature of the Universe that we live in, and how structures evolve and interact on large scales. One of the biggest puzzles in this area is the (relatively) recent finding that the expansion of the Universe appears to be accelerating. This is a very curious result, and I'd like to get to the bottom of it!
There are many different approaches that can be taken to study the apparent acceleration. I'm particularly interested in the effects of inhomogeneities on cosmological observations, and testing the assumptions that go into building cosmological models. Is General Relativity the correct theory of gravity? How do inhomogeneities distort light from the distant objects that we observe when measuring the acceleration? What's the best way of constructing a cosmological model from observations of the real, complicated, inhomogeneous Universe? By answering these questions, we can strengthen the foundations of modern cosmology, and gain valuable insights into the nature of the cosmic acceleration.
I'm also interested in the interaction between theory and observation. We are continually discovering exciting new ways of measuring the cosmos, so it's important to develop methods to exploit these data in interesting ways. Two particularly promising classes of observables are intensity mapping with the neutral hydrogen 21cm emission line, and secondary anisotropies of the CMB, which include the thermal and kinematic Sunyaev-Zel'dovich effects and blackbody spectral distortions. Their potential as cosmological probes will be realised in the near future as more sensitive radio and CMB experiments like the SKA and Advanced ACTPol start delivering data, so it's important to build up our theoretical understanding of them right now.
My technical interests are quite broad, and include:
Cosmology with intensity maps of the redshifted hydrogen 21cm line
Using secondary anisotropies and spectral distortions of the CMB as cosmological probes
General relativistic effects in large-scale structure observations and light propagation
Long-range peculiar velocity surveys and tests of gravity using the kinematic Sunyaev-Zel'dovich effect
Observational tests of the Cosmological Principle, and the averaging and backreaction problems
Bayesian statistics, stochastic processes, and computational physics
Square Kilometre Array (Core Team, Cosmology Science Working Group)
Planck (LFI core team, 2013-2015)
Magnus Fagernes Ivarsen (Masters, Oslo, 2015-16)
Magnus worked on a project to compare peculiar velocity statistics in different modified gravity theories, using halo catalogues from large-scale structure simulations. His aim was to determine whether velocity statistics are useful for studying the environment-dependence of modified gravity effects. If so, they may constitute a valuable new way of observing screening mechanisms at work in alternative gravity theories. You can read the resulting paper here.
Robert Olav Fauli (Masters, Oslo, 2014-15)
Robert wrote a Masters thesis about the effects of modified gravity on peculiar velocity statistics (particularly pairwise velocities). He found substantial differences between several theories over a range of distance scales. You can find his thesis here.
Mikael Bull Steen (PhD, Oslo, 2014-2016)
Mikael was working on a unified classification of relativistic light propagation models before transitioning into industry.
Yashar Akrami (ITP Heidelberg)
David Alonso (Oxford)
Tessa Baker (Oxford)
Chris Clarkson (Cape Town)
Tim Clifton (Queen Mary)
Mark Dijkstra (Oslo)
Hans Kristian Eriksen (Oslo)
Pedro G. Ferreira (Oxford)
Max Grönke (Oslo)
Marc Kamionkowski (Johns Hopkins)
Thibaut Louis (IAP Paris)
Roy Maartens (UWC/ICG Portsmouth)
Mario Santos (CENTRA/IST/UWC)
Dag Sverre Seljebotn (Oslo)
Matteo Viel (INAF/OATS Trieste)
Francisco Villaescusa-Navarro (INAF/OATS Trieste)
Ingunn Wehus (Oslo)
My DPhil (PhD) was supervised by Pedro Ferreira in Oxford, and Tim Clifton, now at Queen Mary, University of London.