Abstract
Minimal scenarios with light (sub-GeV) dark matter whose relic density is obtained from thermal freeze-out must include new light mediators. In particular, a very well-motivated case is that of a new “dark” massive vector gauge boson mediator. The mass term for such mediator is most naturally obtained by a “dark Higgs mechanism” which leads to the presence of an often long-lived dark Higgs boson whose mass scale is the same as that of the mediator. We study the phenomenology and experimental constraints on two minimal, self-consistent dark sectors that include such a light dark Higgs boson. In one the dark matter is a pseudo-Dirac fermion, in the other a complex scalar. We find that the constraints from BBN and CMB are considerably relaxed in the framework of such minimal dark sectors. We present detection prospects for the dark Higgs boson in existing and projected proton beam-dump experiments. We show that future searches at experiments like Xenon1T or LDMX can probe all the relevant parameter space, complementing the various upcoming indirect constraints from astrophysical observations.
Highlights
Such dark gauge groups have been often used in a dark matter context due to their interesting properties and experimental prospects for detection
We find that the constraints from Big Bang Nucleosynthesis (BBN) and CMB are considerably relaxed in the framework of such minimal dark sectors
Most of the literature on the field either focused on the dark Higgs boson, with or without the dark photon, or assumed that it decouples from the rest of the spectrum and concentrated on the dark matter and the dark photon only
Summary
We present two minimal, self-consistent dark sector models for a sub-GeV dark matter. A complex scalar S with charge qS, called “dark Higgs boson” It spontaneously breaks the dark gauge group through a VEV, vS;. The gauge and matter content that we are considering implies that the dark sector can be coupled to the SM either through kinetic mixing between the two abelian gauge groups or by mixing between the SM Higgs H and the dark Higgs boson S. While both portals are a priori open, in this article we will focus on the vector portal. Notice that after diagonalizing the gauge kinetic terms, dark sector particles remain neutral under electromagnetism, but Standard Model fields acquire an -suppressed coupling to the dark photon.
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