Abstract
Multi-component dark matter scenarios constitute natural extensions of standard single-component setups and offer attractive new dynamics that could be adopted to solve various puzzles of dark matter. In this work we present and illustrate properties of a minimal UV-complete vector-fermion dark matter model where two or three dark sector particles are stable. The model we consider is an extension of the Standard Model (SM) by spontaneously broken extra U(1)_X gauge symmetry and a Dirac fermion. All terms in the Lagrangian which are consistent with the assumed symmetry are present, so the model is renormalizable and consistent. To generate mass for the dark-vector X_mu the Higgs mechanism with a complex singlet S is employed in the dark sector. Dark matter candidates are the massive vector boson X_mu and two Majorana fermions psi _pm . All the dark sector fields are singlets under the SM gauge group. The set of three coupled Boltzmann equations has been solved numerically and discussed. We have performed scans over the parameter space of the model implementing the total relic abundance and direct detection constraints. The dynamics of the vector-fermion dark matter model is very rich and various interesting phenomena appear, in particular, when the standard annihilations of a given dark matter are suppressed then the semi-annihilations, conversions and decays within the dark sector are crucial for the evolution of relic abundance and its present value. Possibility of enhanced self-interaction has been also discussed.
Highlights
Dark matter could be searched for through indirect detection experiments, which assume that in regions of large dark matter (DM) density, its pairs are likely to annihilate
As it has been discussed in the previous section the model discussed here simplifies in various regions of the parameter space where it reduces to a single-component dark matter mode i.e. fermion dark matter (FDM) or vector dark matter (VDM)
Multi-component dark matter scenarios are natural extensions of a simple weakly interacting massive particles (WIMPs) dark matter. They predict more than one stable component in a dark sector and they constitute a much richer dynamical structure
Summary
Dark matter could be searched for through indirect detection experiments, which assume that in regions of large DM density, its pairs are likely to annihilate. The model is minimal in a sense that it contains only three new fields in the dark sector; a dark gauge boson Xμ, a Dirac fermion χ , and a complex scalar S, which serves as a Higgs field in the hidden sector They are singlets under the SM gauge group but they are all charged under the dark U (1)X gauge symmetry and they interact with each other. [85], (3) a very small/large mass splitting among the dark sector states (vector and Majorana fermions) are possible without large tuning of the parameters, (4) our model is a gauged version of the model considered by Weinberg [86] for different purposes, and (5) more importantly the minimality of the model; since there is only one parameter, the dark gauge coupling coupling gx, which controls the dynamics in the dark sector, including the conversion, semi-annihilation and decay processes. We supplement our work with an “Appendix A”, collecting details of the derivation of Boltzmann equations, and an “Appendix B”, describing the method adopted to obtain constraints for a multi-component DM model by direct detection experiments
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