Spontaneous emission by a system of N two-level atoms in terms of the SU(2)-group representations

We consider cooperative spontaneous emission by an assembly of N two-level atoms immersed in a high-Q single-mode cavity, when s (s≪N) atoms are initially excited. The atoms are noninteracting with each other except via the action of the electromagnetic field. The eigenvalues of the system and the time development of the mean energy of the atomic subsystem are presented in the form of power series in the parameter ε=(N-s/2+1/2${)}^{\mathrm{-}1}$ using the SU(2)-group-representation technique.