Browsing by Subject "Boltzmann equation"

Particle dark matter (DM) as a solution to the missing mass problem in astronomy has been examined widely and with different models. Among the most studied are weakly interacting massive particles, WIMPs, for short. As dark matter constitutes roughly a quarter of the energy budget of the universe, and due to its vital role in galaxy structures through gravitational interaction, the motivation to uncover the nature and properties of it is strong. In this master’s thesis, a specific particle dark matter model is examined. The model consists of a hidden dark sector added to the Standard Model of Particle Physics (SM). The dark sector introduces a new SU(2) gauge field that acts as a vector dark matter candidate, as well as a complex SU(2) scalar field and interactions between the two. Due to spontaneous symmetry breaking, the dark vector gains a non-zero mass. This relocation of degrees of freedom allows us to write the dark scalar field as having only one real degree of freedom. The dark scalar field also experiences mass mixing with the SM Higgs field, leaving the two propagating scalar mass eigenstates as superpositions of the dark scalar field and the Higgs field. One of these is then identified as the observed Higgs field with a mass of 125 GeV. The four free parameters of the model can be chosen as the masses of the dark matter candidate and the propagating dark scalar field, the angle of the rotation between mass and gauge eigenbasis in the scalar sector and the dark gauge coupling constant. To produce the observed relic density of dark matter, the DM particles need to pair-annihilate with a cross section of order 1.64 × 10^(−9) GeV^(−2). Further constraints are given by collider and direct detection experiments, leaving the parameter space of the model rather constrained. Depending on the values of the other free parameters, a viable mass range of around 100-200 GeV is found for the vector dark matter. The possibility of probing the properties of dark matter through experiments and observations exists. The existence and properties of the dark scalar field could be examined in the Large Hadron Collider. Possible phenomena in the scalar sector of the model, such as phase transitions, could be studied with upcoming gravitational wave detectors, namely the Laser Interferometer Space Antenna. Direct detection experiments provide a way of seeking the dark matter particle itself. With all these possibilities, the future seems interesting.