Abstract
Dark matter candidates arise naturally in many models that address the hierarchy problem. In the fraternal twin Higgs model which could explain the absence of the new physics signals at the Large Hadron Collider (LHC), there are several viable dark matter candidates. In this paper we study the twin neutrino in the mass range ∼ 0.1–10 GeV as the dark matter. The thermal relic density is determined by the interplay of several annihilation and scattering processes between the twin neutrino, twin tau, and twin photon, depending on the order of the freeze-out temperatures of these processes. Besides the common coannihilation scenario where the relic density is controlled by the twin tau annihilation, it can realize the recently discovered coscattering phase if the scattering of the twin neutrino into the twin tau freezes out earlier than the twin tau annihilation. We also provide a method to calculate the thermal relic density in the intermediate regime where both coannihilation and coscattering processes contribute to the determination of the dark matter density. We show that the right amount of dark matter can be obtained in various scenarios in different regions of the parameter space. The current experimental constraints and future probes into the parameter space from direct detections, cosmological and astrophysical bounds, dark photon searches, and displaced decays at colliders, are discussed.
Highlights
In the fraternal twin Higgs model which could explain the absence of the new physics signals at the Large Hadron Collider (LHC), there are several viable dark matter candidates
The thermal relic density is determined by the interplay of several annihilation and scattering processes between the twin neutrino, twin tau, and twin photon, depending on the order of the freeze-out temperatures of these processes
If twin hypercharge is gauged, the preferred mass is lighter, in the 1– 20 GeV range [4]. Another possibility is asymmetric dark matter from the twin baryon made of twin b-quarks, where the relic density is set by the baryon asymmetry in the twin sector [5, 6]
Summary
The twin Higgs model postulates a mirror (or twin) sector which is related to the SM sector by a Z2 symmetry. One can take a minimal approach to avoid these light particles by only requiring the Z2 symmetry on the parts which are most relevant for the hierarchy problem This is the fraternal twin Higgs (FTH) model proposed in ref. The twin bottom and twin leptons are required for anomaly cancellation, but their Yukawa couplings do not need to be equal to the corresponding ones in the SM, as long as they are small enough to not generate a big contribution to the Higgs potential. It is found that a right amount of thermal relic abundance can be obtained for a twin tau mass in the range of 50–150 GeV if the twin hypercharge is not gauged [3, 4].
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