Bounds on Compositeness from Neutrinoless Double Beta Decay
  Assuming the existence of a heavy Majorana neutral particle arising from a composite model scenario we discuss the constraints imposed by present experimental limits of half-life neutrinoless double beta decay $(0\nu\beta\beta ) $ measurements on the coupling of the heavy composite neutrinos to the gauge bosons. For neutrino masses $M_N = 1 $ TeV we obtain a rather weak lower bound on the compositeness scale: $\Lambda \ge 0.23 $ TeV. 
Orlando Panella and Yogendra N. Srivastava