  A R&D project, named Nano5, has been recently launched to study an
architectural design in view of addressing new experimental issues related to
particle transport in high energy physics and other related physics disciplines
with Geant4. In this frame, the first step has involved the redesign of the
photon interaction models currently available in Geant4; this task has
motivated a thorough investigation of the physics and computational features of
these models, whose first results are presented here.
