My research is aimed at understanding the history of the universe. Based on a variety of observations, we believe that the universe evolved through a number of distinct eras, each characterized by the dominant form of energy that filled the universe at that time. The earliest known era is called inflation, a period of exponential growth of the universe. The details of how inflation occurred are not known, although there are many proposals.

Each era in the history of the universe is not independent. The evolution of the universe during one era will determine the initial conditions for the next. One dramatic example is that quantum mechanical fluctuations during inflation eventually grew to form everything from stars to galaxy clusters. It is through these connections that we can learn about the very early universe.

As theorists, our goal is to find new opportunities to learn about these eras through their impact on observable quantities. I have pursued this goal primarily in the context of inflation. One successful approach has been to further our understanding of the physics of inflation looking for new ways to test the framework. On some occasions, this involves looking for novel scenarios where the predictions my differ qualitatively from more conventional models. In other cases, we can look to understand conventional models sufficiently well that we can identify specific observations that would rule them out, without necessarily having a compelling alternative.

More recently, I have been interested in new aspects of our thermal history that may be observable in the next generation of cosmic microwave background (CMB) experiments. A percent-level measurement of the total energy density in radiation during the radiation-era would be sensitive to any particle that was ever in thermal equilibrium with the Standard model and would transform our understanding of light relics and physics beyond the Standard Model more generally. Rapid improvements in CMB detector sensitivity are making such a measurement a reality for the next generation of observations, opening a window back to the time of reheating. New theoretical tools need to be developed for this new realm of ultra-high precision and to connect cosmological observations with other experiments.  Ongoing work is revealing implications for axions, neutrinos and dark matter that will have significant implications for other branches of physics.