Multi-component dark matter models with new interactions

This work is devoted to the study of three different models of dark matter,
which include non-standard interactions with ordinary matter or with itself, and
their effects in cosmology and astrophysics. Multi-component dark matter models
include more than one sort of new fundamental particles and their interactions and
typically have richer phenomenology. The introduction of such additional candidates
allows to explain various observational discrepancies in astrophysics or cosmology
and/or offers new possibilities to probe the nature of dark matter.
The excess of high-energy cosmic positrons above the astrophysical prediction
can have a dark matter origin. We show that, however, dark matter explanations of
this phenomenon, which assume a conventional density distribution in the Galaxy,
are in serious tension with the observations of the isotropic gamma-ray background.
As a possible alternative explanation, we investigate the model of self-interacting
dark matter, which forms a disk and alleviates the problem with gamma-ray mea-
surements.
Some models of strongly interacting massive particles (SIMPs) might produce
the signal in the DAMA detector and explain the contradiction with the results
of other direct detection experiments. We study the propagation of SIMPs in the
ground and demonstrate that such models cannot reproduce the time-dependent
features of the observed rate of events.
The 3-Higgs-Doublet Model (3HDM) with the CP symmetry of order 4 is the
simplest extension of the Higgs sector that allows to stabilize potential dark matter
candidates without any additional symmetries. This model contains a new inter-
action that converts one dark matter candidate into another and leads to novel
phenomenology of asymmetric dark matter. We describe the cosmological ther-
mal evolution of dark matter density in this model and discuss the perspectives of
indirect detection.