Sasaki-Einstein Manifolds

This article is an overview of some of the remarkable progress that has been made in Sasaki-Einstein geometry over the last decade, which includes a number of new methods of constructing Sasaki-Einstein manifolds and obstructions.Comment: 58 pages. Invited contribution to Surveys in Differential Geometry. v2: references and discussion adde

Symplectic Techniques for Semiclassical Completely Integrable Systems

This article is a survey of classical and quantum completely integrable systems from the viewpoint of local ``phase space'' analysis. It advocates the use of normal forms and shows how to get global information from glueing local pieces. Many crucial phenomena such as monodromy or eigenvalue concentration are shown to arise from the presence of non-degenerate critical points.Comment: 32 pages, 7 figures. Review articl

Lectures on quantization of gauge systems

A gauge system is a classical field theory where among the fields there are connections in a principal G-bundle over the space-time manifold and the classical action is either invariant or transforms appropriately with respect to the action of the gauge group. The lectures are focused on the path integral quantization of such systems. Here two main examples of gauge systems are Yang-Mills and Chern-Simons.Comment: 63 pages, 22 figures. Based on lectures given at the Summer School "New paths towards quantum gravity", Holbaek, Denmark, 200

On minimal eigenvalues of Schrodinger operators on manifolds

We consider the problem of minimizing the eigenvalues of the Schr\"{o}dinger operator H=-\Delta+\alpha F(\ka) ($\alpha>0$) on a compact $n-$manifold subject to the restriction that \ka has a given fixed average \ka_{0}. In the one-dimensional case our results imply in particular that for F(\ka)=\ka^{2} the constant potential fails to minimize the principal eigenvalue for \alpha>\alpha_{c}=\mu_{1}/(4\ka_{0}^{2}), where $\mu_{1}$ is the first nonzero eigenvalue of $-\Delta$. This complements a result by Exner, Harrell and Loss (math-ph/9901022), showing that the critical value where the circle stops being a minimizer for a class of Schr\"{o}dinger operators penalized by curvature is given by $\alpha_{c}$. Furthermore, we show that the value of $\mu_{1}/4$ remains the infimum for all $\alpha>\alpha_{c}$. Using these results, we obtain a sharp lower bound for the principal eigenvalue for a general potential. In higher dimensions we prove a (weak) local version of these results for a general class of potentials F(\ka), and then show that globally the infimum for the first and also for higher eigenvalues is actually given by the corresponding eigenvalues of the Laplace-Beltrami operator and is never attained.Comment: 7 page

Compact Einstein Spaces based on Quaternionic K\"ahler Manifolds

We investigate the Einstein equation with a positive cosmological constant for $4n+4$-dimensional metrics on bundles over Quaternionic K\"ahler base manifolds whose fibers are 4-dimensional Bianchi IX manifolds. The Einstein equations are reduced to a set of non-linear ordinary differential equations. We numerically find inhomogeneous compact Einstein spaces with orbifold singularity.Comment: LaTeX 28 pages, 5 eps figure