  In this paper we further elaborate on our recently proposed solution to the
cosmological constant problem - Phys. Rev. D82 (2010) 044006. One of the
elements of the solution is the chameleonic behaviour of the Einstein frame
dilaton: the mass of the dilaton is an increasing function of the matter
density. In that model, a proper structure of the string-frame form factors in
the strong coupling region of string theory is assumed. In particular, a
stabilizing potential of the string frame dilaton is present and it is supposed
to be the result of a quantum calculation. Our main purpose in this article is
to point out that the lagrangian of the chameleonic model for the dilaton can
be embedded, to a large extent, in heterotic-M-theory. We illustrate some
theoretical grounds that support the ansatz about the form factors. In this
paper, we break bulk supersymmetry with a massive sterile spinor field (i.e. a
bulk neutrino field) and, under certain assumptions about the full M-theory
action, we point out the Casimir origin of the stabilizing potential for the
string frame dilaton (particular attention is dedicated to the role of the
conformal transformations involved). Moreover, we point out the similarity
between the string frame dark matter lagrangian and a Ginzburg-Landau
lagrangian with sterile neutrino pairs playing the role of dark matter
particles. However, more research efforts are necessary to connect the bulk
spinor (neutrino) lagrangian with the Ginzburg-Landau lagrangian through direct
calculations. A phenomenological test of these ideas is definitely required.
