Existence, non-existence and multiplicity results for some third-order periodic problems

This talk concerns the solvability of third-order periodic problems with a weighted parameter, where the nonlinearity must verify only a local monotone condition and no periodic, coercivity, or super or sublinearity restrictions are assumed, as usual in the literature.
The arguments are based on a new type of lower and upper solutions, not necessarily well ordered. A Nagumo growth condition and Leray–Schauder’s topological degree theory are the existence tools.
A nonlinear third-order differential model for periodic catatonic phenomena, depending on biological and/or chemical parameters, is presented.