Multidimensional phase space and sunset diagrams

We derive expressions for the phase space of a particle of momentum p decay ing into N particles, that are valid for any number of dimensions. These ar e the imaginary parts of so-called "sunset" diagrams, which we also obtain. The results are given as a series of hypergeometric functions, which termi nate for odd dimensions and are also well suited for deriving the threshold behavior. (C) 2001 American Institute of Physics.