Working with students and collaborators, much of my research focuses on measurements of the cosmic microwave background (CMB). The CMB, which pervades the universe, is the thermal afterglow of the big bang. Detailed knowledge of the magnitude and pattern of the fluctuations in temperature from spot to spot on the sky, or anisotropy, and its polarization tell us how the universe evolved and how the observed structure, at sizes ranging from galaxies to superclusters of galaxies, was formed. From precise measurements of the CMB, we can deduce many of the cosmological parameters and the physics of the very early universe. For example, we have been able to determine the geometry and age of the universe, the cosmic density of baryons, the cosmic density of dark matter, and show that the fluctuations that seeded cosmic structure are adiabatic and Gaussian.

This is an exciting time for cosmology. The experimental tools and techniques, coupled with theory, have developed to the point were we can probe the physics of the infant universe in wonderful detail and we can use the cosmos to measure, for example, the sum of the neutrino masses. There are many cosmologists at Princeton and a number work on CMB related projects. On the theoretical front, there are Jo Dunkley, Jim Peebles, David Spergel, Paul Steinhardt, and Matias Zaldarriaga at the IAS. On the experimental front, there are Norm Jarosik, Bill Jones, Lyman Page, and Suzanne Staggs. 

The other part of my research involves the search for wave-like dark matter or, more specifically, axions. In the standard model of cosmology, 25% of the cosmic energy density is dark matter but we don’t know what it is. Our standard model of particle physics, while very successful, does not explain the absence of an electric dipole moment in the neutron. One particularly promising solution related to both these open questions is the QCD axion. These are pseudoscalar particles associated with Peccei-Quinn symmetry breaking. They could be the dark matter and explain the lack of the neutron’s electric dipole moment. The research at Princeton is being done in collaboration with Saptarshi Chaudhuri.