About

My main research interest is weak gravitational lensing as a tool to study large structures in the Universe, such as galaxies and clusters of galaxies [1,2,3,4]. The census and evolution of these structures is interesting in its own right, but it can also give us a better understanding of two of the greatest mysteries of modern physics, dark matter and dark energy. To reach that goal, we need to develop new methods in statistics and data analysis for the extraction of reliable and powerful information from optical surveys.

I am co-coordinator of the weak lensing working group of the Dark Energy Survey, the leading weak lensing experiment to date. DES recently released its first competitive cosmological constraints [5,6,7,8]. These were announced in the live-streamed talk shown below, which is also an introduction of how to use lensing for cosmology.

I did my PhD [9] and a brief post-doc at University Observatory Munich and the Max Planck Institute for extraterrestrial Physics, before moving to Stanford as a post-doctoral researcher and NASA Einstein Fellow in the X-ray Astronomy and Observational Cosmology group of Prof. Steve Allen. At Stanford, I also collaborate a lot with the Galaxy Formation and Cosmology group of Prof. Risa Wechsler, and with Prof. Aaron Roodman's group at SLAC

I have devised a new density split statistic to measure the full probability distribution function of the matter density field [10]. With the Dark Energy Survey, I have used those measurements for unprecedented tests of gravity beyond the power spectrum and improved constraints on cosmology [11,12].

I use machine learning and other data science techniques to develop new statistical methods for accurate weak lensing measurements, especially for estimating and calibrating photometric redshifts [13,14]. The new methods I developed to that end [15] have motivated the final major observing program of the Dark Energy Survey, explained in this video.



I have worked on developing new ways of measuring shapes of faint background galaxies. In the course of this work, I also got interested in the correction of instrumental features [16] required for precision analyses. I have also done the actual data reduction and weak lensing analysis of a number of clusters of galaxies, among them the pictures you see on top of this page.

If you are a student and interested in getting involved in the next generation of gravitational lensing research: please contact me about opportunities for rotations / projects for visiting students / internships.