Exactly solvable models and bifurcations: the case of the cubic $NLS$ with a $δ$ or a $δ'$ interaction

Abstract: We explicitly give all stationary solutions to the focusing cubic NLS on the line, in the presence of a defect of the type Dirac's delta or delta prime. The models proves interesting for two features: first, they are exactly solvable and all quantities can be expressed in terms of elementary functions. Second, the associated dynamics is far from being trivial. In particular, the $NLS$ with a delta prime potential shows two symmetry breaking bifurcations: the first concerns the ground states and was already known. The second emerges on the first excited states, and up to now had not been revealed. We highlight such bifurcations by computing the nonlinear and the no-defect limits of the stationary solutions.