Signature transition in Einstein–Cartan cosmology

Abstract In the context of Einstein–Cartan theory of gravity, we consider a Friedmann–Lemaitre–Robertson–Walker (FLRW) cosmological model with Weyssenhoff perfect fluid. We focus attention on those classical solutions that admit a degenerate metric in which the scale factor has smooth behavior in the transition from a Euclidean to a Lorentzian domain. It is shown that the spin–spin contact interaction enables one to obtain such a signature changing solutions due to the Riemann–Cartan ( U 4 ) structure of space–time.