H. Berestycki et al., EIGENVALUE PROBLEMS FOR SOME NONLINEAR WHEELER-DEWITT OPERATORS, Journal de mathematiques pures et appliquees, 72(5), 1993, pp. 493-515
In this paper we study the existence and non-existence of solutions of
the form e(ilambday)u(x), u not-equal 0, for a nonlinear model of the
simplified Wheeler-DeWitt equation.