MG11 
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Dark matter decay and annihilation influence upon structure formation

DM decays and annihilations might heat and ionize the primordial IGM, affecting its thermal and chemical evolution. We investigate whether they can also change the "critical mass" which is needed for a primordial halo to cool and form stars. This is done through a 1-D hydrodynamical code, where we included the treatment of the chemical evolution of the gas, and of the effects of different models of DM decays/annihilations. The results are mixed: in some cases (e.g. sterile neutrinos) the critical mass remains almost unchanged; in other cases (e.g. light dark matter decays) it increases significantly. In fact, the enhanced ionized fraction catalyzes H2 formation and favours cooling, but this is not sufficient to compensate for the effects (e.g. the increase in the Jeans mass) of the extra heating.