We develop a supervised dimensionality reduction method, called Lorentzian discriminant projection (LDP), for feature extraction and classification. Our method represents the structures of sample data by a manifold, which is furnished with a Lorentzian metric tensor. Different from classic discriminant analysis techniques, LDP uses distances from points to their within-class neighbors and globa...

We consider an asymptotically flat Lorentzian manifold of dimension (1, 3). An inequality is derived which bounds the Riemannian curvature tensor in terms of the ADM energy in the general case with second fundamental form. The inequality quantifies in which sense the Lorentzian manifold becomes flat in the limit when the ADM energy tends to zero.

we study umbilic (space-like) submanifolds of pseudo-riemannian space forms, then define totally semi-umbilic space-like submanifold of pseudo euclidean space and relate this notion to umbilicity. finally we give characterization of total semi-umbilicity for space-like submanifolds contained in pseudo sphere or pseudo hyperbolic space or the light cone.a pseudo-riemannian submanifold m in (a ps...

The formalism of Greensite for treating the spacetime signature as a dynamical degree of freedom induced by quantum fields is considered, for spacetimes with nontrivial topology of the kind R ×T1, for varying D. It is shown that a dynamical origin for the Lorentzian signature is possible in the five-dimensional space R × T with small torus radius (periodic boundary conditions), as well as in fo...

We review the finding that the general solution of many physically relevant (bosonic) Einstein-matter systems in the vicinity of a cosmological, i.e. space-like, singularity exhibit a remarkable mixture of chaos and symmetry. On the one hand, the asymptotic behavior, as one approaches the singularity, of the general solution is found to be describable, at each (generic) spatial point, as a bill...

This work is a combinatorial study of quantum gravity models related to Lorentzian quantum gravity. These models are discrete combinatorial objects called dynamical triangulations. They are related to classical combinatorial objects: Dyck paths, heaps, . . . This work is in collaboration with Xavier Viennot and is part of the speaker’s thesis [4]. Quantum gravity is a quantum description of the...

We study the geometric structure of Lorentzian spin manifolds, which admit imaginary Killing spinors. The discussion is based on the cone construction and a normal form classification of skew-adjoint operators in signature (2, n−2). Derived geometries include Brinkmann spaces, Lorentzian Einstein-Sasaki spaces and certain warped product structures. Exceptional cases with decomposable holonomy o...

This paper develops a supervised dimensionality reduction method, Lorentzian Discriminant Projection (LDP), for discriminant analysis and classification. Our method represents the structures of sample data by a manifold, which is furnished with a Lorentzian metric tensor. Different from classic discriminant analysis techniques, LDP uses distances from points to their within-class neighbors and ...