Nonconformal Scalar Field in a Homogeneous Isotropic Space and the Hamiltonian Diagonalization Method

We diagonalize the metric Hamiltonian and evaluate the energy spectrum of the corresponding quasiparticles for a scalar field coupled to a curvature in the case of an $N$-dimensional homogeneous isotropic space. The energy spectrum for the quasiparticles corresponding to the diagonal form of the canonical Hamiltonian is also evaluated. We construct a modified energy-momentum tensor with the following properties: for the conformal scalar field, it coincides with the metric energy-momentum tensor; the energies of the particles corresponding to its diagonal form are equal to the oscillator frequency; and the number of such particles created in a nonstationary metric is finite. We show that the Hamiltonian defined by the modified energy-momentum tensor can be obtained as the canonical Hamiltonian under a certain choice of variables.