Gravity-induced four-fermion contact interaction implies gravitational   intermediate W and Z type gauge bosons
  Coupling fermions to gravity necessarily leads to a non-renormalizable, gravitational four-fermion contact interaction. In this essay, we argue that augmenting the Einstein-Cartan Lagrangian with suitable kinetic terms quadratic in the gravitational gauge field strengths (torsion and curvature) gives rise to new, massive propagating gravitational degrees of freedom. This is to be seen in close analogy to Fermi's effective four-fermion interaction and its emergent W and Z bosons. 
Jens Boos and Friedrich W. Hehl
gr-qc hep-ph