Abstract
A pseudo Nambu-Goldstone boson (pNGB) is a natural candidate of dark matter in that it avoids the severe direct detection bounds. We show in this paper that the pNGB has another different and interesting face with a higher symmetry breaking scale. Such large symmetry breaking is motivated by various physics beyond the standard model. In this case, the pNGB interaction is suppressed due to the Nambu-Goldstone property and the freeze-out production does not work even with sufficiently large portal coupling. We then study the pNGB dark matter relic abundance from the out-of-equilibrium production via feeble Higgs portal coupling. Further, a possibility is pursued the symmetry breaking scalar in the pNGB model plays the role of inflaton. The inflaton and dark matter are unified in a single field and the pNGB production from inflaton decay is inevitable. For these non-thermally produced relic abundance of pNGB dark matter and successful inflation, we find that the dark matter mass should be less than a few GeV in the wide range of the reheating temperature and the inflaton mass.
Highlights
One of the ways naturally evading the severe constraints from direct detection is to identify a pseudo Nambu-Goldstone boson as dark matter
We find that the self-coupling λΦ should be in the range λΦ 10−12 in the pseudo Nambu-Goldstone boson (pNGB) dark matter model with large symmetry breaking, if the inflation is induced by the coupling ξ
The pNGB dark matter can be regarded as a natural FIMP candidate if the vacuum expectation value (VEV) of the symmetry-breaking scalar is large enough
Summary
We are interested in the case that both of dark matter χ and the CP-even scalar φ ( h2) are never thermalized with the SM particles. A radiative correction to the |Φ|4 term would imply its lower bound, λΦ λ2HΦ/16π2 With these feeble couplings, both of φ and χ become the FIMPs, and the Boltzmann equations for the number densities nφ and nχ are given by dnφ dt. The collision terms are written by using the thermally averaged cross sections and the number density of the SM Higgs doublet in thermal bath, neHq. we obtain. The first term in the right-hand side denotes the dark matter production directly from the thermal bath, and the second and third terms are the contributions from the decays of. This behavior implies that even if the portal coupling λHΦ is large, the dark matter reaction rate with the SM is suppressed in lower energy than mφ and the usual freeze-out does not work in the case of the hierarchical VEV vφ v (mφ mh)
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