Abstract
If fermionic dark matter (DM) is stabilized by dark U(1) gauge symmetry that is spontaneously broken into its subgroup Z2, the particle contents of the model becomes very rich: DM and excited DM, both of them are Majorana fermions, as well as two dark force mediators, dark photon and dark Higgs boson are naturally present due to the underlying dark gauge symmetry. In this paper, we study the DM bound state formation processes within this scenario, assuming both dark photon and dark Higgs are light mediators and including the effects of excited DM. The Goldstone boson contributions to the potential matrix in the Schrödinger equations are found to be important. The emissions of a longitudinal vector boson (or somehow equivalently a Goldstone boson) during the DM bound state formations are crucial to induce a significant reannihilation process, reducing the dark matter relic abundance. Most of the stringent constraints for this kind of dark matter considered in the literature are simply evaded.
Highlights
From the view point of particle physics described by quantum field theory, one of the most important and fundamental properties of dark matter (DM) is that it should be absolutely stable or long-lived enough in order to make DM of the Universe
If fermionic dark matter (DM) is stabilized by dark U(1) gauge symmetry that is spontaneously broken into its subgroup Z2, the particle contents of the model becomes very rich: DM and excited DM, both of them are Majorana fermions, as well as two dark force mediators, dark photon and dark Higgs boson are naturally present due to the underlying dark gauge symmetry
In particular if some of them are light, they can play the role of light mediators which are often introduced to the DM phenomenology in order to solve some puzzles in the vanilla cold dark matter (CDM) paradigm
Summary
We start from a dark U(1) model, with a Dirac fermion dark matter (DM) χ appointed with a nonzero dark U(1) charge Qχ and dark photon. The kinetic mixing term (∝ ) and the Higgs portal interaction (∝ λΦH ) communicate the dark and the standard model sectors. The λΦH is constrained by collider searches for the exotic and invisible Higgs decay widths and the direct detections of fermionic Higgs-portal dark matter. Χ2 had all decayed away, so (2.11) is absent when we consider the indirect detection constraints
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