Probing the early universe with a generalized action.

Possibly, the most general action in the background of isotropic and homogeneous space-time has been considered to study the quantum evolution of the early universe. 'Hermiticity' of the effective Hamiltonian operator in the presence of curvature squared terms suggests unitary time evolution of the quantum states, assuring the conservation of probability. Oscillatory behaviour of the semi-classical wavefunction signals that the theory is classically allowed. Despite the presence of several coupling parameters, only one additional slow-roll condition is required to impose in order to study the inflation. Inflationary parameters lie well within the presently available Planck's data. Since the Gauss-Bonnet-dilatonic coupled term does not play any roll in the inflationary regime, it appears to play a significant roll in the late stage of cosmic evolution.