A general proof of the equivalence between the \delta N and covariant
  formalisms
  Recently, the equivalence between the \delta N and covariant formalisms has
been shown (Suyama et al. 2012), but they essentially assumed Einstein gravity
in their proof. They showed that the evolution equation of the curvature
covector in the covariant formalism on uniform energy density slicings
coincides with that of the curvature perturbation in the \delta N formalism
assuming the coincidence of uniform energy and uniform expansion (Hubble)
slicings, which is the case on superhorizon scales in Einstein gravity. In this
short note, we explicitly show the equivalence between the \delta N and
covariant formalisms without specifying the slicing condition and the
associated slicing coincidence, in other words, regardless of the gravity
theory.
