Geometric models of matter

Inspired by soliton models, we propose a description of static particles in terms of Riemannian 4-manifolds with self-dual Weyl tensor. For electrically charged particles, the 4-manifolds are non-compact and asymptotically fibred by circles over physical 3-space. This is akin to the Kaluza-Klein description of electromagnetism, except that we exchange the roles of magnetic and electric fields, and only assume the bundle structure asymptotically, away from the core of the particle in question. We identify the Chern class of the circle bundle at infinity with minus the electric charge and, at least provisionally, the signature of the 4-manifold with the baryon number. Electrically neutral particles are described by compact 4-manifolds. We illustrate our approach by studying the Taub-Newman, Unti, Tamburino (Taub-NUT) manifold as a model for the electron, the Atiyah-Hitchin manifold as a model for the proton, CP2 with the Fubini-Study metric as a model for the neutron and S-4 with its standard metric as a model for the neutrino.