'Mass of neutrino species'

@property
def m_nu(self):

    if (self._Tnu0.value == 0):
        return None
    if (not self._massivenu):
        return u.Quantity(np.zeros(self._nmasslessnu), u.eV, dtype=np.float)
    if (self._nmasslessnu == 0):
        return u.Quantity(self._massivenu_mass, u.eV, dtype=np.float)
    numass = np.append(np.zeros(self._nmasslessnu), self._massivenu_mass.value)
    return u.Quantity(numass, u.eV, dtype=np.float)
