Generalised matter couplings in massive bigravity
  We investigate matter couplings in massive bigravity. We find a new family of
such consistent couplings, including and extending known consistent matter
couplings, and we investigate their decoupling limits, ADM decompositions,
Higuchi bounds and further aspects. We show that differences to previous known
consistent couplings only arise beyond the $\Lambda_3$ decoupling limit and
discuss the uniqueness of consistent matter couplings and how this is related
to the so-called symmetric vielbein condition. Since we work in a vielbein
formulation, these results easily generalise to multi-gravity.
