Gravity from Spinors

We investigate the proposal that a unified theory of all interactions could be based only on fundamental spinor fields, with vielbein and metric arising as composite objects. The effective gravitational theory leads to a modification of Einstein’s equations due to the lack of local Lorentz-symmetry. We explore the generalized gravity with global instead of local Lorentz symmetry in first order of a systematic derivative expansion. The effective action suggested by the one loop approximation to spinor gravity is consistent with all present tests of general relativity and cosmology. In contrast, a further coupling allowed by the symmetries is restricted by present solar system observations. We also discuss different geometrical viewpoints of spinor gravity. e-mail: [email protected]