Gravitational Lensing

In observational cosmology, gravitational lensing has developed into an important tool. It is uniquely able to measure mass distributions around galaxies and clusters, without any assumptions on equilibrium, equation of state, or orbital structure. On the largest scales it offers the possibility to measure directly the power spectrum of the distribution of dark matter, which when combined with the fluctuations observed in the cosmic microwave background forms a powerful probe of the matter content of the universe. Inside galaxies, lensing is the best probe of the dark matter distribution’s shape and extent as it surrounds the visible galaxies.

Given the recent leaps in our statistical knowledge of the nearby universe (particularly through the 2dF and SDSS redshift surveys) and the universe at redshift 1100 (from the CMB), this workshop will focus on where lensing constraints can bring their weight to bear. There will be a mixture of overview talks and technical discussions, on optimal statistics for cosmological parameter estimation, lensing effects on the CMB, on weak lensing constraints on the evolution of angular diameter distance with redshift, on measuring and calibrating gravitational shear, on substructure constraints on dark haloes, etc. In this fast-moving field we will endeavour to stress the most topical results of next summer, hopefully including the next instalment of WMAP results, and first results from the on-going CFHT or soon-to-start VST lensing surveys.

More technically, we will bring together a number of participants in the ’Shear Testing Programme’, a year-old collaboration in which teams around the world are performing blind tests of their image analysis software on huge, realistically simulated data sets. The goal of the programme is to explore the limits of the different methods in use today for measurement of gravitational lensing shear, and to set a benchmark for future development.

As a result of the workshop we hope to gain a better understanding of the interplay between different constraints on the geometry of the universe, and on the properties of dark halos. Also a clear understanding of the state of the art of weak lensing measurements should be achieved.