Any sphere S admits a metric of constant sectional curvature. These canonical metrics are homogeneous and Einstein, that is the Ricci curvature is a constant multiple of the metric. The spheres S, m > 1 are known to have another Sp(m + 1)-homogeneous Einstein metric discovered by Jensen [Jen73]. In addition, S has a third Spin(9)-invariant homogeneous Einstein metric discovered by Bourguignon a...

The spinor representation is developed and used to investigate minimal surfaces in R with embedded planar ends. The moduli spaces of planar-ended minimal spheres and real projective planes are determined, and new families of minimal tori and Klein bottles are given. These surfaces compactify in S to yield surfaces critical for the Möbius invariant squared mean curvature functional W . On the ot...

Because there are only a few problems in statistical mechanics that can be solved exactly, we need to find approximate solutions. We introduce several perturbation methods that are applicable when there is a small expansion parameter. Our discussion of interacting classical particle systems will involve some of the same considerations and difficulties that are encountered in quantum field theor...

We formulate the notion of equivariance of an operator with respect to a covariant representation of a C∗-dynamical system. We then use a combinatorial technique used by the authors earlier in characterizing spectral triples for SUq(2) to investigate equivariant spectral triples for two classes of spaces: the quantum groups SUq(l+1) for l > 1, and the odd dimensional quantum spheres S q of Vaks...

In a path-integral approach to quantum cosmology, the Lorenz gaugeaveraging term is studied for Euclidean Maxwell theory on a portion of flat four-space bounded by two concentric three-spheres, but with arbitrary values of the gauge parameter. The resulting set of eigenvalue equations for normal and longitudinal modes of the electromagnetic potential cannot be decoupled, and is here studied wit...

We examine an extension of the ideas of quantum cosmology and, in particular, the proposal of Hartle and Hawking for the boundary conditions of the Universe, to models which incorporate Yang-Mills fields. Inhomogeneous perturbations about a homogeneous, isotropic minisuperspace background model are considered, by expanding the Yang-Mills fields in harmonics of the spatial directions which are t...

A family of quantum systems parametrized by the points of a compact space can realizeits classical symmetries via a new kind of nontrivial ray representation. We show that thisphenomenon in fact occurs for the quantum mechanics of fermions in the presence ofbackground gauge fields, and is responsible for both the nonabelian anomaly and Witten’sSU(2) anomaly. This provides a hamiltonian interpre...

(Joint work with Alexandru Chirvasitu.) The Borsuk-Ulam theorem in algebraic topology indicates restrictions for equivariant maps between spheres; in particular, there is no odd map from a sphere to another sphere of lower dimension. This idea may be generalized greatly in both the topological and operator algebraic settings for actions of compact (quantum) groups, leading to the the noncommuta...