Matter-antimatter asymmetry and dark matter from torsion
  We propose a simple scenario which explains the observed matter-antimatter
imbalance and the origin of dark matter in the Universe. We use the
Einstein-Cartan-Sciama-Kibble theory of gravity which naturally extends general
relativity to include the intrinsic spin of matter. Spacetime torsion produced
by spin generates, in the classical Dirac equation, the Hehl-Datta term which
is cubic in spinor fields. We show that under a charge-conjugation
transformation this term changes sign relative to the mass term. A classical
Dirac spinor and its charge conjugate therefore satisfy different field
equations. Fermions in the presence of torsion have higher energy levels than
antifermions, which leads to their decay asymmetry. Such a difference is
significant only at extremely high densities that existed in the very early
Universe. We propose that this difference caused a mechanism, according to
which heavy fermions existing in such a Universe and carrying the baryon number
decayed mostly to normal matter, whereas their antiparticles decayed mostly to
hidden antimatter which forms dark matter. The conserved total baryon number of
the Universe remained zero.
