A Hidden Valley model of cold dark matter with photonic portal
  In the discussed model, the cold dark matter consists of Dirac spin-1/2 fermions, sterile from all Standard Model charges, where masses are generated by a nonzero vacuum expectation value of a field of scalar bosons, also assumed to be sterile. For convenience, these sterile particles have beeen called sterinos and sterons, respectively. It has been conjectured that our sterile world of sterinos and sterons can communicate with the familiar Standard Model world not only through gravity, but also through a photonic portal provided by a very weak effective interaction involving the electromagnetic field F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu A_\mu coupled to the sterino and steron fields. 
Wojciech Krolikowski