Non linear Fierz-Pauli theory from torsion and bigravity

Understand

The non linear aspects of a recently proposed model of massive spin-2 particles with propagating torsion are studied.

• We obtain a nonlinear equation which reduces at linear order to a generalized Fierz-Pauli equation in any background space-time with or without a vanishing torsion.
• We contrast those results with properties of a class of bigravity theories in an arbitrary background Einstein manifold.
• It is known that the non perturbative spectrum of the bigravity model has 8 propagating physical degrees of freedom.