Gauge vectors and double beta decay
  We discuss contributions to neutrinoless double beta ($0\nu\beta\beta$) decay involving vector bosons. The starting point is a list of all possible vector representations that may contribute to $0\nu\beta\beta$ decay via $d=9$ or $d=11$ operators at tree-level. We then identify gauge groups which contain these vectors in the adjoint representation. Even though the complete list of vector fields that can contribute to $0\nu\beta\beta$ up to $d=11$ is large (a total of 46 vectors), only a few of them can be gauge bosons of phenomenologically realistic groups. These latter cases are discussed in some more detail, and lower (upper) limits on gauge boson masses (mixing angles) are derived from the absence of $0\nu\beta\beta$ decay. 
Renato M. Fonseca, Martin Hirsch
hep-ph