Quantum mechanical probability interpretation in the mini-superspace model of higher order gravity theory

It has been shown that introduction of higher order curvature invariant terms like R2 or RμνRμν in the Robertson–Walker minisuperspace model of the Einstein–Hilbert action leads to Schrödinger-like equation, whose corresponding effective Hamiltonian is hermitian. Thus, it is possible to write the continuity equation in a straightforward manner which reveals a quantum mechanical probability interpretation of the theory.