Neutrinoless double β decay with composite neutrinos

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Abstract
We study in detail the contribution of heavy composite Majorana neutrinos to neutrinoless double beta decay (0νββ). Our analysis confirms the result of a previous estimate by two of the authors. Excited neutrinos couple to the electroweak gauge bosons through a magnetic-type effective Lagrangian. The relevant nuclear matrix element is related to matrix elements available in the literature and current bounds on the half-life of 0νββ are converted into bounds on the compositeness scale and/or the heavy neutrino mass. Our bounds are of the same order of magnitude as those available from accelerator experiments.