My major research interest is in theoretical cosmology, with a
specific interest in the study of cosmological
perturbations. In the standard big-bang
framework of cosmology, a hot, dense, smooth universe begins in a
rapidly expanding state. As the universe continues to expand, the
temperature becomes cooler, the material in the universe becomes less
dense, and the expansion rate slows down. As the universe cools,
light elements can form (such as deuterium, helium-3 and helium-4, and
lithium). Eventually, it cools so much that neutral atoms can
form (leaving a relic, decoupled photon background), and the expansion
rate slows to that observed today. These three observations, the light
element abundances, the cosmic
microwave radiation background, and the Hubble expansion
of the universe, are the three cornerstones of big bang
cosmology. However, the universe is not perfectly smooth, it is full of
and clusters. The entire
structure of the universe, then, must grow out of a universe which is
mostly smooth, but not quite perfectly smooth. These
imperfections in the early universe are known as cosmological perturbations, and
their creation, evolution, and impact on the universe are my primary
fields of research.
The discussion of cosmological perturbations allows us to ask a number
of questions about their relation to the universe. Some of these
What created these imperfections in the early universe?
Is there a difference between the initial fluctuations on
Are these fluctuations adiabatic, isocurvature, or a mix?
Is the spectrum of these fluctuations Gaussian? If so, when
does processing become important?
How does structure form in a perturbed universe like this?
Can these gravitational inhomogeneities impact the overall
When cosmological perturbations grow, do they have important
My research has attempted to address some of these issues, and this is
an ongoing project. So far, we have found that growing
cosmological perturbations create magnetic fields on all scales, that
the gravitational inhomogeneities do impact the expansion rate, but the
effect is small, and that in the presence of the right types of extra
dimensions, the cosmological perturbations in gravitational radiation
can have wildly different properties. My Ph.D.
dissertation is on the subject of these cosmological perturbations and
their effects on the universe. Additionally, a list of my
publications is below:
Probing Dark Matter Substructure with Pulsar Timing [In