  Collective modes in two dimensional topological superconductors are studied
by an extended random phase approximation theory while considering the
influence of vector field of light. In two situations, the s-wave
superconductors without spin-orbit-coupling (SOC), and the hybrid semiconductor
and s-wave superconductor layers with strong SOC, we get the analytical results
for longitudinal modes which are found to be indeed gapless. Further more, the
effective modes volumes can be calculated, the electric and magnetic fields can
be expressed as the creation and annihilation operators of such modes. So, one
can study the interaction of them with other quasi-particles through fields.
