Abstract
A strongly interacting massive particle (SIMP) is an interesting candidate for dark matter (DM) because its self-interaction cross section can be naturally strong enough to address the astrophysical problem of small-scale structure formation. A simple model was proposed by assuming a monopole condensation, where composite SIMP comes from a "strongly interacting" U(1)$_{\rm d}$ gauge theory. In the original model, the DM relic abundance is determined by the $3\to2$ annihilation process via the Wess-Zumino-Witten term. In this letter, we discuss that the DM relic abundance is naturally determined also by a semi-annihilation process via a kinetic mixing between the hypercharge gauge boson and the dark U(1)$_{\rm d}$ gauge boson (dark photon). The dark photon can be discovered by LDMX-style missing momentum experiments in the near future.
Highlights
The intensity frontier is one of the broad approaches to new physics in collider experiments and recently became more important as the Large Hadron Collider has not yet found a clear signal for new physics
In Ref. [21], we have proposed a simple model of the strongly interacting massive particle (SIMP), where the composite dark matter (DM) “pions” consist of darksector “electrons” and “positrons” connected by a Uð1Þd
The “monopole” and the gauge boson are assumed to be heavier than the “pions,” which we identify as DM
Summary
The intensity frontier is one of the broad approaches to new physics in collider experiments and recently became more important as the Large Hadron Collider has not yet found a clear signal for new physics. There is a difficulty in maintaining thermal equilibrium between the dark and visible sectors during the freeze-out of the 3 → 2 annihilation process, which is required for the SIMP miracle to work This can be realized in rather complicated models like the ones proposed in Refs. We revisit our SIMP model and propose a scenario in which the DM relic abundance is determined by a 2 → 2 semiannihilation process [33] via the kinetic mixing between the Uð1Þd gauge boson and Uð1ÞY gauge boson rather than the 3 → 2 annihilation process. We assume that the Uð1Þd gauge symmetry is spontaneously broken by a “monopole” condensation at the energy scale of 0.1–1 GeV, below which there are “pions.” We calculate its self-interaction cross section and show that it is within the value potentially favored by the observations of small-scale structure. We comment on the mixing between the SM Higgs boson and the “monopole.” Section IV is devoted to conclusions
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