We give a unified description of tetrahedra with lightlike faces in 3d anti-de Sitter, de Sitter and Minkowski spaces their duals hyperbolic half-pipe spaces. show that both types are determined by generalized cross-ratio values commutative 2d real algebra generalizes the complex numbers. Equivalently, pair edge lengths dihedral angles. prove dual precisely ideal introduced Danciger. Finally, w...

A criterion for a spacelike hypersurface in a conformally stationary spacetime to be a Cauchy hypersurface is given. The criterion is based on the forward and the backward completeness of a non-reversible Finsler metric associated to the hypersurface.

A 6-component “wave function” (not field, but S-matrix interpretable) for a massive spin-1 particle parallels the Dirac “chiralitydoubled” 4-component wave function for a spin-1/2 particle, by pairing two wave functions for same spin but opposite “handedness”. The correlated “opposite-parity” pair of complex 3-vectors defines a fluctuating spin-correlated lightlike “internal velocity” as well a...

A result of Mason, as refined by Ingleton, characterizes transversal matroids as the matroids that satisfy a set of inequalities that relate the ranks of intersections and unions of nonempty sets of cyclic flats. We prove counterparts, for fundamental transversal matroids, of this and other characterizations of transversal matroids. In particular, we show that fundamental transversal matroids a...

Certain criteria are demonstrated for a spatial derivation of a von Neumann algebra to generate a one-parameter semigroup of endomorphisms of that algebra. These are then used to establish a converse to recent results of Borchers and of Wiesbrock on certain one-parameter semigroups of endomorphisms of von Neumann algebras (specifically, Type III1 factors) that appear as lightlike translations i...

Eastwood and Ezhov generalized the Cayley surface to the Cayley hypersurface in each dimension, proved some characteristic properties of the Cayley hypersurface and conjectured that a homogeneous hypersurface in affine space satisfying these properties must be the Cayley hypersurface. We will prove this conjecture when the domain bounded by a graph of a function defined on Rn is also homogeneou...