My research is largely focused on the extremes of the cosmic web of matter. This mesh-like structure evolves over billions of years, seeded by intial small variations in the density of the Universe. I study how over- and under-densities on the largest scales evolve across cosmic history. This work involves studying the statistical properties of clusters and voids in the distribution of galaxies during the last few billion years of the history of the Universe. 

The statistical properties of these extremes of the cosmic web are highly sensitive to e.g. the properties of dark energy and dark matter, the behaviour of gravity in untested regimes, and the masses of neutrinos.

I develop and perform measurements of this and other physics, using observations. For this, I am a member of the 4MOST Cosmology and Cluster surveys, the Euclid Consortium Theory Working Group, the Square Kilometer Array Cosmology Working Group, the XMM Cluster Survey, and the XXL Survey. I am an external collaborator in the Dark Energy Survey.

Recent work includes the demonstration of the power of clusters and voids as probes of deviations from General Relativitythe first cosmological parameter estimation based on voids, and discovery of a powerful new test of modified gravity theories. A popular-science overview is available in Swedish in Populär Astronomi 2, 2016.

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