Anze Slosar

My main focus is constraining the microscopic description of the standard cosmological model through available cosmological data.

Publications

Oliver Zahn

My cosmological interests include the microwave background primary and secondary anisotropies, red-shifted 21 cm radiation, gravitational lensing, dark energy, reionization, dark matter, and inflation.

Publications

Alexie Leauthaud

Current research:

I am involved in lensing measurements with COSMOS, the largest contiguous HST survey to date. My main focus at the moment is to measure galaxy-galaxy lensing signals around elliptical galaxies in order probe the dark matter halos in which they reside.

I am investigating the nature of the dark universe. Although we can see a great amount of stars, galaxies and dust in the Universe, many independent measurements now agree that the combined mass in these ordinary, baryonic systems is insufficient to account for more than a few percent of the entire budget. The standard hypothesis to explain the missing mass is an additional but mysterious "dark matter" component, which interacts with ordinary baryons only through the force of gravity. It is said to be "dark" because it does not interact through electromagnetism, and therefore neither emits nor reflects light. So dark matter cannot be seen directly - but, for example, its additional gravity makes galaxies rotate faster than they otherwise would. One potential candidate for dark matter is the least massive of the (as-yet unobserved) supersymmetric particles.

Evidence has also been found for an even stranger component known as "dark energy". This acts as a repulsive force on very large scales. The universe has been expanding since the Big Bang, but now it its large, dark energy is accelerating that expansion. One consequence of this acceleration is that high redshift objects, which we see via light emitted a long time ago, appear further away (so fainter) than expected.

I probe the dark universe via measurements of weak gravitational lensing, the deflection of light from distant galaxies by intervening gravitational potentials. This is a purely geometrical effect, free from astrophysical biases and sensitive to all mass - regardless of its baryonic or dark form. Gravitational lensing measurements have a uniquely dual ability to probe both the growth of structure (which is dominated by the distribution of dark matter) as well as the geometrical distance-redshift relation (which traces the expansion history of the universe and can thus distinguish between a cosmological constant and more esoteric forms of dark energy). The mounting observational evidence for dark matter and dark energy challenge the standard model of particle physics and General Relativity's prediction for the behaviour of gravity on large scales. Almost all of existing scientific knowledge concerns the baryons, and determining the nature of these phenomena is widely viewed as one of the most outstanding problems in physics.