I am a theoretical physicist, and my research is in cosmology, astrophysics, and elementary-particle theory.  My primary  research interests vary from year to year, but my main focus has been on particle dark matter, inflation and the cosmic microwave background, and cosmic acceleration.  I have also worked on neutrino and nuclear physics and astrophysics, large-scale-structure and galaxy formation, gravitational waves, gravitational lensing, phase transitions in the early Universe, alternative-gravity theories, the first stars and the epoch of reionization, and a bit in stellar and high-energy astrophysics.

I am a member of the Theoretical Astrophysics (Including Relativity) group and the recently established Moore Center for Theoretical Cosmology and Physics, both in the Division of Physics, Mathematics, and Astronomy at Caltech.  My interests also overlap with our particle- theory and nuclear-theory (Kellogg Radiation Laboratory) groups and with a variety of experimental groups here in cosmology, astrophysics, and nuclear and high-energy physics.    I teach classes in both the Departments of Physics and Astronomy.