Existence of infinitely many solutions for second-order singular initial value problems with an application to nonlinear massive gravity

We prove the existence of infinitely many solutions for a second-order singular initial value problem between given lower and upper solutions. Our study is motivated by a singular problem which arises in the field of nonlinear massive gravity. Moreover, we also discuss the global behavior of solutions of the motivating problem. Our arguments lean at some steps on lower and upper solutions with corners in their graphs, thus showing the applicability of this more general definition of lower and upper solutions in the analysis of a concrete mathematical model.