Physics of counterion mediated attractions between double-stranded DNAs

Attraction between two indentical objects uniformly charged in solution seems intuitively surprising on the one hand because we know that such objects do repel in vacuum and on another hand because this simple mental picture is still preserved within the Poisson-Boltzmann theory of ion-mediated interactions. We will see, however, that by relaxing some contraints on the models used, one can find ion-mediated attraction between uniformly charged objects in solution. This allows to give some insights on the possible way two DNA double strands attract each other in many biologically relevant cases.