Charting the Unknown: the Hunt for Dark Matter Continues

Abstract

For thousands of years, the human mind struggles to answer a simple question: what is the universe made of? The majority of what composes our universe, dark matter and dark energy, are just mysteries. Undoubtedly, dark matter is one of the most interesting fundamental puzzles of our universe. While we have accumulated sufficient cosmological evidence supporting its existence, the character of the dark matter particle is still unknown. The widely successful theory of elementary particles, the standard model, is incapable of providing an interpretation of the dark matter puzzle, pressing towards new theories. A myriad of models have been proposed, the majority of which introduce a single dark matter candidate for simplicity. Though they provide testable hypotheses at various experiments, little attempt has been made beyond single-candidate dark matter. In this thesis, we go beyond single-candidate dark matter by focusing on two-component dark matter candidates. Surprisingly, their phenomenology is very different from that of single-candidate, providing a new avenue for dark matter experiments. In particular, we examine a novel thermal dark matter scenario where present-day annihilation of dark matter in the galactic center or in the Sun may produce subdominant but detectable boosted stable particles via neutral-current-like interactions. We scrutinize various scenarios where such dark matter of spin 0 and 1/2 interacts with electrons via an exchange of vector, scalar, axial-vector or pseudo-scalar mediators. Detailed detection prospects due to high or moderate Lorentz-boosted particles are studied at deep neutrino experiments and traditional direct detection experiments. We stress that the extension of dark matter models with more than one candidate beyond the minimal dark matter model opens up a new window for various experiments. Such a theoretical investigation and multiple experimental probes will advance our knowledge about dark matter and perhaps lead to its discovery in the near future.