Gravitational energy from a quadratic Lagrangian with torsion with torsion

Gravitation is considered as a gauge field within the formalism of Utiyama (Phys. Rev.; 101:1597 (1956)) and Kibble (J. Math. Phys.; 2:219 (1961)). In empty space-time a Lagrangian density, quadratic in Riemann's curvature tensor and in Cartan's torsion tensor, is introduced. The equations of motion are coupled differential equations for the curvature and torsion tensors. The spin of the torsion field behaves as a curvature source and the energy of both fields acts as a torsion source. Each field has an energy tensor, similar to the Maxwell tensor of electrodynamics, vanishing in a torsionless space. It thus appears that the torsion of space-time is a geometric property that makes possible the propagation of gravitational energy in the absence of matter. (author)