Complementary probes of the nature of dark matter

There is overwhelming evidence for the existence of a nonbaryonic dark matter (DM) component in the Universe's energy budget, coming from various astrophysical and cosmological probes, but its nature is very much unknown. A plethora of models have been proposed, mostly under the umbrella of the particle DM paradigm. The desired properties of DM indicates that it is only natural to expect that a viable DM candidate lies in extensions of the Standard Model (SM). In this work, we have considered minimal models that address the so-called DM puzzle, which are also motivated by theoretical issues and experimental anomalies in the SM. Firstly, motivated by the possibility that the nonbaryonic component could be described by a dark sector framework that is as complex as the SM, we consider a scenario in which DM resides in a multicomponent dark sector. The stable species are charged under an unbroken U(1) dark force, mediated by a massless dark photon, and they also interact with ordinary matter through scalar portals. We study its implications on cosmology, by studying its early Universe evolution through the numerical solution of a set of Boltzmann equations which track the relic densities and the temperatures of the dark and visible sectors. On the other hand, the reported discrepancy between the SM prediction and the recently announced experimental measurement of the muon magnetic dipole moment is addressed from the point of view of new physics. Here we introduced a minimal model, inspired by the MSSM, where the bino-like Majorana fermion is regarded as the DM candidate, while other species such as the sleptons are necessary to both alleviate the tension in the muon g-2, as well as to produce the correct relic density of DM. Meanwhile, the attempt to understand the nature of DM is not only limited to tracking its early Universe history nor to provide solutions to experimental anomalies, but also by probing it in relaxed structures, that have formed at late times, such as the halo in our own Milky Way (MW) galaxy. DM in the MW halo can be probed through direct detection searches, which rely on observing possible recoil signals induced by scatterings of DM with nuclei or with electrons. Deriving direct detection limits on DM requires the calculation of the theoretical recoil signal, which involves specifying the elementary interaction of DM with ordinary matter, as well as properly assessing the systematic uncertainties coming from nuclear physics, atomic physics, and astrophysics. Here we focus on quantifying the astrophysical uncertainty which enters in the assumption for the velocity distribution of DM in the MW. We advocate the implementation of equilibrium axisymmetric modeling to describe the DM phase space distribution function (PSDF). This has the advantage of being self-consistent with the MW mass model, which is axisymmetric and is well-supported by latest kinematic data on tracers of the underlying MW gravitational potential. We assess the impact of the axisymmetric PSDF particularly on DM-electron scattering, which is an excellent probe of sub-GeV DM, and compare the resulting exclusion limits coming from the Standard Halo Model (SHM) that is often quoted in the literature.