MG15 - Talk detail

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Abstract

In the talk I review briefly the three most important problems where tensions between predictions based on numerical simulations of the Lambda-CDM prototype and observations at small (galactic) scales occur. These include (i) the core-cusp problem on the galactic profiles, (ii) the missing satellite problem, and the (ii) too-big-to-fail problem. I explain what these problems are and present potential resolutions, first through some astrophysical mechanisms, which however, as I argue, fail to alleviate completely the problems, at least currently. Then, I discuss fundamental modifications/extensions of the Lambda-CDM model, through, e.g. the inclusion of self-interacting dark matter (SIDM). I argue that a particularly simple model of SIDM, with (warm) self-interacting right-handed neutrinos (RHN), that exist in minimal extensions of the Standard model of particle physics, appears particularly promising in providing a resolution of the aforementioned ``small-scale-Cosmology crisis''. The important feature of such models is that the RHN may only constitute part of the Dark Matter (DM) in the universe, so that at large scales the predictions of the Lambda-CDM model are still valid, while at galactic scales the role of RHN is crucial in providing agreement of the predicted galactic structure and the pertinent DM distribution with observations. I also speculate that one may modify, with relative ease, the dark energy sector of such SIDM models, e.g. to incorporate features and concepts from the so-called ``running vacuum model'' framework, which may provide further help in reconciling theory with observations.

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