Self Interacting Dark Matter in the Solar System
  Weakly coupled, almost massless, spin 0 particles have been predicted by many extensions of the standard model of particle physics. Recently, the PVLAS group observed a rotation of polarization of electromagnetic waves in vacuum in the presence of transverse magnetic field. This phenomenon is best explained by the existence of a weakly coupled light pseudoscalar particle. However, the coupling required by this experiment is much larger than the conventional astrophysical limits. Here we consider a hypothetical self-interacting pseudoscalar particle which couples weakly with visible matter.   Assuming that these pseudoscalars pervade the galaxy, we show that the solar limits on the pseudoscalar-photon coupling can be evaded. 
Avijit K. Ganguly, Pankaj Jain, Subhayan Mandal and Sarah Stokes