Production of new cosmological perturbations during the radiation-dominated era

PURCELL (unpublished data) has noted the tendency for ‘dust’ particles strongly to cluster when they are coupled by viscous drag to a ‘gas’ whose velocity field is stochastic: where α(s−1) is the viscous coupling constant. The application of the Purcell clustering effect to cosmology which is considered here generates relatively large isothermal perturbations from relatively small adiabatic perturbations which will not otherwise survive damping during recombination.