On extended sign-changeable interactions in the dark sector
  We extend the cosmological couplings proposed in Sun et al. and Wei, where
they suggested interactions with change of signs along the cosmological
evolution. Our extension liberates the changes of sign of the interaction from
the deceleration parameter and from the relation of energy densities of the
dark sector and considers the presence of non interactive matter. In three
cases we obtain the general solutions and the results obtained in models fitted
with Hubble's function and SNe Ia data, are analyzed regarding the problem of
the cosmological coincidence, the problem of the crisis of the cosmological age
and the magnitude of the energy density of dark energy at early universe. Also
we graphically study the range of variation of, the actual dark matter density
parameter, the effective equation of state of the dark energy and the redshift
of transition to the accelerated regimen, generated by variations at order
$1\sigma$ in the coupling parameters.
