IIB matrix model is one of the candidates for nonperturbative formulation of the string theory.
While the coordinates are represented by matrices in the original interpretation, the matrices are interpreted as a covariant derivative in the “derivative interpretation.” The advantage of the representation is the manifest diffeomorphism invariance.
We calculate the low-energy effective action in the derivative interpretation and find that it is expressed as a sum of terms, each of which is factorized into a product of diffeomorphism invariant action functionals. This form of the action can be interpreted as describing a multiverse where the universes are connected by wormholes. I will also discuss the locality and the relation to realistic models.