Scientific Series

Understanding how galaxies form is a major current goal in physical cosmology: although a basic picture is well-accepted, there are outstanding mysteries to be solved. First, what is the origin of the heavy elements seen outside of galaxies? Given that these elements are created only inside galaxies, there must be a process whereby galaxies can expel gas rather than accrete it. Second, galaxy properties are somewhat different from theory predicts, yet extremely regular -- to the extent that it has been seriously argued that modified gravity, rather than dark matter, explains them. I will discuss these mysteries and the possibility that the same culprit -- galactic winds -- may play a key role in solving both.

It was conjectured that the N=4 Yang-Mills perturbation theory in the sector with large R charges corresponds to considering the classical string worldsheets in $AdS_5imes S^5$ as perturbations of the null-surfaces. We discuss this perturbation theory with a special emphasis on a hidden symmetry.

We discuss collective coordinate quantization of the half-BPS geometries of Lin, Lunin and Maldacena (hep-th/0409174). The LLM geometries are parameterized by a single function u on a plane. We treat this function as a collective coordinate. We arrive at the collective coordinate action as well as path integral measure by considering D3 branes in an arbitrary LLM geometry. The resulting functional integral is shown, using known methods (hep-th/9309028), to be the classical limit of a functional integral for free fermions in a harmonic oscillator. The function u gets identified with the classical limit of the Wigner phase space distribution of the fermion theory which satisfies u * u = u. The calculation shows how configuration space of supergravity becomes a phase space (hence noncommutative) in the half-BPS sector. Our method sheds some new light on counting supersymmetric configurations in supergravity.