SEZIONE DI FIRENZE
I will discuss the thermodynamic history of models with composite Dark Matter candidates. A particular focus is directed at the role of number-changing interactions in the dark plasma. Those are generically present among glueballs and pions in the composite phase of gauge theories and significantly affect the freeze-out and behaviour of the dark sector. We develop a consistent formalism to take into account the non-trivial thermodynamic effects in Boltzmann equations and provide asymptotic analytical solutions. Within the composite Dark Matter framework we identify several viable models. One class of models has long lived dark baryons as Dark Matter candidates, in the other class of models the dark plasma particles, such as pions can be the Dark Matter candidates. The third possibility is a multicomponent scenario, where the dark baryons provide the dominant Dark Matter component and the dark plasma particles are a subdominant light Dark Matter population. In this scenarios !
the subdominant fraction of light Dark Matter particles feature significant self-scattering cross sections and might alleviate the tension in observations of the matter power spectrum. (Juri Smirnov)