Probing hidden sectors with Stückelberg U(1) gauge fields.

We propose a framework in which visible matter interacts with matter from a hidden sector through mass mixings of Stückelberg U(1) gauge fields. In contrast to other Z(') mediation scenarios, our setup has the added appealing features that (i) the choice of Z(')'s can be significantly broadened without necessarily introducing unwanted exotic matter and (ii) there can be sizable tree-level interactions between the visible and hidden sectors. String theory embeddings of this scenario and their phenomenological features are briefly discussed.