  A fundamental action, representing a mass dimension-transmuting operator
between Dirac and ELKO spinor fields, is performed on the Dirac Lagrangian, in
order to lead it into the ELKO Lagrangian. Such a dynamical transformation can
be seen as a natural extension of the Standard Model that incorporates dark
matter fields. The action of the mass dimension-transmuting operator on a Dirac
spinor field, that defines and introduces such a mapping, is shown to be a
composition of the Dirac operator and the non-unitary transformation that maps
Dirac spinor fields into ELKO spinor fields, defined in a previous paper. This
paper gives allowance for ELKO, as a candidate to describe dark matter, to be
incorporated in the Standard Model. It is intended to present for the first
time, up to our knowledge, the dynamical character of a mapping between Dirac
and ELKO spinor fields, transmuting the mass dimension of spin one-half
fermionic fields from 3/2 to 1 and from 1 to 3/2.
