Special involutions and bulky parabolic subgroups in finite Coxeter   groups
  The conjugacy classes of so-called special involutions parameterize the constituents of the action of a finite Coxeter group on the cohomology of the complement of its complexified hyperplane arrangement. In this note we give a short intrinsic characterisation of special involutions in terms of so-called bulky parabolic subgroups. 
Goetz Pfeiffer and Gerhard Roehrle