On the three-particle analog of the Lellouch-L\"uscher formula

Using non-relativistic effective field theory, we derive a three-particle analog of the Lellouch-L"uscher formula at the leading order. This formula relates the three-particle decay amplitudes in a finite volume with their infinite-volume counterparts and, hence, can be used to study the three-particle decays on the lattice. The generalization of the approach to higher orders is briefly discussed.