I'm studying the existence and uniqueness of a solution and its asymptotic behaviour to the following problem
\begin{align} & -\Delta u +\epsilon u = f \text{ on } \Omega \\ & \dfrac{\partial u}{\partial \nu}= g \text{ on } \Gamma \end{align}
through variational formulations and Sobolev spaces.
Where $\Omega$ is the domain, $\Gamma$ its border and $\epsilon > 0$.
Does anyone know where I can find resources for this type of problem ? Thanks.