I am a cosmologist, and have worked on understanding the nature of dark matter, gravitational lensing, the cosmic microwave background radiation, spectroscopy of the rarefied matter in the intergalactic medium, and the nature of quasars and galaxies at high-redshift. Three attributes essentially characterize my research. First, I work at the interface between observations and theory --- this typically involves collecting and analyzing data, but I prefer to work on theoretically demanding and well posed problems. Recently, a common theme has been to search for rare objects which constitute unique astrophysical laboratories, which requires mining databases of hundreds of millions of celestial objects provided by modern digital sky surveys. Finally, I conduct observations with the world's largest telescopes and most powerful instruments.

Currently I am mostly focused on studying diffuse gas in the intergalactic and circumgalactic medium using quasar absorption line techniques, and I lead the ENIGMA research group at UCSB dedicated to this purpose.