Dirac and pseudo-Dirac neutrinos and neutrinoless double beta decay

A recent assertion by Enqvist, Maalampi and Mursula that it is possible to introduce a conserved quantum number in such a way that the neutrino is strictly a Dirac particle but neutrinoless double beta ((ββ)sub(0ν)) decay is allowed, is shown to be false. It is explicitly shown that if (ββ)sub(0ν) decay is allowed, then the (electron) neutrino acquires a Majorana mass at some level. Contrary to the conclusion of these authors, it is also shown that (ββ)sub(0ν) is strictly forbidden in the specific model they consider. (orig.)