Comment on "Can gravity distinguish between Dirac and Majorana neutrinos?".

In a recent letter[1], Singh, Mobed and Papini (hereafter referred to as (I)) claim to show that the gravitaional field associated with the Lense-Thirring metric can distinguish between Dirac and Majorana neutrinos. According to these authors, the matrix element of the interaction Hamiltonian is significantly different, depending on the Dirac or Majorana nature of the neutrino. Here we point out that the treatment of Majorana neutrinos in (I) is not valid, due to an incorrect definition and construction of the spinor that corresponds to a Majorana particle. As a consequence, the results of this paper concerning Majorana neutrinos are not valid, and in particular the major claim stated above does not follow. The Majorana condition is a requirement on the fermion field operator ψ, viz., that it should be selfconjugate up to a phase factor ξ,