Quantum Fields and Strings

The cosmic microwave background (CMB) is our most direct cosmological observable, encoding critical information about the evolution and development of the universe. The Wilkinson Microwave Anisotropy Probe (WMAP) has measured the angular power spectrum of the CMB temperature and temperature-polarization power spectra with unprecedented accuracy from its first year in flight. These recent observations along with developments in supernovae and galaxy surveys are generating critical challenges for theoretical physics, producing fundamental, intriguing questions in particle physics, cosmology and astrophysics that are as yet unresolved. We discuss in this seminar how the theoretical picture of the nature of dark matter and dark energy, and the origins of the universe, is being guided and modified by observations.

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.