Refracted Levy processes

Motivated by classical considerations from risk theory, we investigate boundary crossing problems for refracted L\'evy processes. The latter is a L\'evy process whose dynamics change by subtracting off a fixed linear drift (of suitable size) whenever the aggregate process is above a pre-specified level. More formally, whenever it exists, a refracted L\'evy process is described by the unique strong solution to the stochastic differential equation $$\D U_t = - \delta \mathbf{1}_{\{U_t >b\}}\D t + \D X_t$$ where $X=\{X_t :t\geq 0\}$ is a L\'evy process with law $\mathbb{P}$ and $b, \delta\in \mathbb{R}$ such that the resulting process $U$ may visit the half line $(b,\infty)$ with positive probability. We consider in particular the case that $X$ is spectrally negative and establish a suite of identities for the case of one and two sided exit problems. All identities can be written in terms of the $q$-scale function of the driving L\'evy process and its perturbed version describing motion above the level $b$. We remark on a number of applications of the obtained identities to (controlled) insurance risk processes.