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
LSST Dark Energy Science Collaboration (full member; Theory and Joint Probes Working Group)
Hydrogen Epoch of Reionization Array (Power Spectrum and Statistics working groups)
Square Kilometre Array (core team; Cosmology Science Working Group)
Planck (LFI core team, 2013-2015)
Lisa McBride (Masters, SFSU, 2018)
Lisa is studying how the mean spectral energy distributions of galactic dust foregrounds depend on the temperature and opacity distribution of dust clouds along each line of sight. Because the emission along each line of sight has contributions from many dust regions with different physical properties, we expect the mean SED to have something other than a simple 'modified blackbody' frequency spectrum. This is not usually accounted for in CMB foreground fits though, so she is working to understand whether this could cause problems for future experiments.
Louis Penafiel (undergrad, UC Riverside, 2017) and Elizabeth Kimura (undergrad, Santa Monica College, 2017)
Louis and Elizabeth spent the summer working at JPL through the FIELDS programme. They wrote, from scratch, a framework to compare the precision of the LSST Core Cosmological Library (CCL) matter power spectrum calculation with that of other codes, like CLASS. Louis (a physics major) wrote a set of scripts to run CCL and CLASS over a large number of sample points in cosmological parameter space, and implemented a web frontend that could dynamically display comparisons between different power spectra. Elizabeth (a computer science major) designed the web interface and developed different ways of presenting the data to make it easy to identify patterns in discrepancies between different methods.
Amanda Brown (undergrad, Princeton, 2016)
Amanda spent the summer of 2016 working at JPL. She took an analytic galaxy-halo model that I developed and compared it with semi-analytic simulations to calibrate the redshift dependence of the star formation rate-stellar mass relation. She then wrote a code to efficiently populate mock halo catalogues with galaxies, using this model as a statistical description of the galaxy populations.
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)
Martin White (UC Berkeley)
My DPhil (PhD) was supervised by Pedro Ferreira in Oxford, and Tim Clifton, now at Queen Mary University of London.