11th Northeast String Cosmology Meeting

This workshop brings together string theorists and cosmologists to discuss new ideas and observations relevant for understanding the universe from very early times until today.

Agenda

Abstracts

Cosmological Constraints from X-ray Studies of Galaxy Clusters
Steve Allen, Stanford

X-ray observations of galaxy clusters provide one of our most powerful probes of cosmology. I will discuss the latest results from two independent experiments based on X-ray cluster studies. The first uses measurements of the baryonic mass fraction in the largest, dynamically relaxed clusters. This method, like type Ia supernovae studies, measures distance as a function of redshift and traces the acceleration of the Universe directly. It also provides a tight constraint on the mean matter density. The second experiment uses observations of the growth of cosmic structure, as manifested in the evolution of the X-ray luminosity function of galaxy clusters. It leads to tight constraints on the amplitude of mass fluctuations in the Universe, and new constraints on dark energy. I will emphasize the allowances for systematic uncertainties incorporated into these experiments and place the results in the context of other current cosmological data. I also will comment on the prospects for improving these results over the next few years.

Observing Brane Inflation
Rachel Bean, Cornell

We discuss how CMB observations can be used to investigate the properties of inflation beyond the slow roll limit, for which observational predictions could differ markedly from those of the standard paradigm. We discuss a variety of brane inflation models which could exhibit rich observational signatures, potentially offering a way to distinguish the underlying microphysical properties of such an inflationary theory.

Geometric Precipices in String Cosmology
Nemanja Kaloper, University of California, Davis

We explain how the dilaton field obstructs transitions between different thermodynamic phases of the string gas, argued to be phenomenologically important for building interesting cosmological scenarios. This happens because the sign of its dimensionally reduced, $T$-duality invariant, part is conserved when the energy density of the universe is positive. Because of this, some of the thermodynamic phases of the usual gravitating string gases behave like superselection sectors. They are separated by curvature singularities, which behave like a geometric precipice in the moduli space, preventing the dynamics of the theory from bridging across. To change this conclusion one must introduce sources which simultaneously violate the positivity of energy and null energy conditions. At present, it is not known how to construct such sources from first principles