  Particles in a hidden sector can potentially acquire a small electric charge
through their interaction with the Standard Model and can consequently be
observed as millicharged particles. We systematically compute the production of
millicharged scalar, fermion and vector boson particles in collisions of
polarized photons. The presented calculation is model independent and is based
purely on the assumptions of electromagnetic gauge invariance and unitarity.
Polarization observables are evaluated and analyzed for each spin case. We show
that the photon polarization asymmetries are a useful tool for discriminating
between the spins of the produced millicharged particles. Phenomenological
implications for searches of millicharged particles in dedicated photon-photon
collision experiments are also discussed.
