Abstract
The null results in dark matter direct detection experiments imply the present scalar dark matter (DM) annihilation cross section to bottom quark pairs through the Higgs boson exchange is smaller than about $10^{-31}$ cm$^3/$s for a wide DM mass range, which is much smaller than the required annihilation cross section for thermal relic DM. We propose models of a thermal relic DM with the present annihilation cross section being very suppressed. This property can be realized in an extra $U(1)$ gauge interacting complex scalar DM, where the thermal DM abundance is determined by coannihilation through the gauge interaction while the present annihilation is governed by Higgs bosons exchange processes. An interaction between DM and the extra $U(1)$ breaking Higgs field generates a small mass splitting between DM and its coannihilating partner so that coannihilation becomes possible and also the $Z'$-mediated scattering off with a nucleon in direct DM search becomes inelastic. We consider scalar dark matter in $U(1)_{B-L}, U(1)_{(B-L)_3}$ and $U(1)_{L_\mu-L_\tau}$ extended models and identify viable parameter regions. We also discuss various implications to future DM detection experiments, the DM interpretation of the gamma-ray excess in the globular cluster 47 Tucanae, the muon anomalous magnetic moment, the Hubble tension and others.
Highlights
Interacting massive particle (WIMP) is a primary candidate for the dark matter (DM) in the Universe
Thermal DM abundance is determined by coannihilation through the gauge interaction while the present annihilation is governed by Higgs bosons exchange processes
Scalar DM annihilating into bbthrough the Higgs boson exchange is naively expected to have the present annihilation cross section be smaller than Oð10−31Þ cm3=s for its wide mass range, which is much more stringent than the limit derived from Fermi-LAT experiment
Summary
Interacting massive particle (WIMP) is a primary candidate for the dark matter (DM) in the Universe. An appealing property of WIMP is its complementarity: If WIMP is a thermal relic from the early Universe, the abundance of DM is determined by the annihilation cross section of the order of picobarn for WIMP annihilation into standard model (SM) particles at thermal freeze-out. As we will explicitly show, a theoretical interpretation of the small scattering cross section of WIMP with a nucleon implies that the present DM annihilation cross section for most of the DM mass range seems smaller than about 10−31 cm3=s which is far below the sensitivity of the current and near-future observations. Thermal DM abundance is determined by coannihilation through the gauge interaction while the present annihilation is governed by Higgs bosons exchange processes.
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