  We consider an extension of the Standard Model with the global symmetry
breaking pattern SO(5)/SO(4), where the Higgs boson arises as a
pseudo-Nambu-Goldstone boson. The scalar content of the theory consists of a
Standard-Model-like Higgs field and an extra real scalar field. The flavour
sector of the model is extended by two right-handed neutrinos compatible with
the observed light-neutrino phenomenology, and we find that the correct vacuum
alignment determines the mass of the heavier neutrino eigenstate to be around
80 TeV. The new singlet-scalar state generates dynamically a Majorana mass term
for the heavy neutrino states. We show how the model leads to the correct
baryon asymmetry of the universe via leptogenesis in the case of two degenerate
or hierarchical heavy neutrinos.
