Effective theories of the Cosmology of Microscopic Physics.

My research proposal aims to develop new, more efficient theories of large-scale properties of the universe by exploiting situations where there is a large hierarchy of physical scales. Just like in atomic physics, where we need only know a few basic properties (i.e. mass, charge) of a nucleus -- but no specific knowledge about the underlying quarks and gluons -- to describe the physics of the hydrogen atom, I hope to consider the cosmology of complicated systems where we can capture the underlying physics with a few, relatively-simple degrees of freedom. In this way, we hope to gain a better understanding of the universe at times even closer to the big bang. In models with extra dimensions, it must be that the size of the extra dimensions must be much smaller than the size of the observable universe; therefore, many of the same techniques apply. I'd like to consider: 1) a specific extra-dimensional model which has been shown to give a reliably small cosmological constant; 2) a more complex, string-motivated extra-dimensional model about which there is some controversy about its cosmology. The techniques used here are ones that are universal to high-energy physics; by thinking concretely about the relevant physics at low energies, I expect to make significant progress in understanding deep questions which lie at the nearboundary of the observable.