  We consider a left-right symmetric model in which neutrinos acquire mass due
to the spontaneous violation of both the gauged $B-L$ and a global $U(1)$
symmetry broken by the vacuum expectation value (VEV) of a gauge singlet scalar
boson $\VEV{\sigma}$. For suitable choices of $\VEV{\sigma}$ consistent with
all laboratory and astrophysical observations neutrinos will be unstable
against majoron emission. All neutrino masses in the keV to MeV range are
possible, since the expected neutrino decay lifetimes can be short enough to
dilute their relic density below the cosmologically required level. A wide
variety of possible new phenomena, associated to the presence of left-right
symmetry and/or the global symmetry at the TeV scale, could therefore be
observable, without conflict with cosmology. The latter includes the
possibility of invisibly decaying higgs bosons, which can be searched at LEP,
NLC and LHC.
