Resurrecting the fraternal twin WIMP miracle

In twin Higgs models that contain the minimal particle content required to address the little hierarchy problem (i.e., fraternal models), the twin tau has been identified as a promising candidate for dark matter. In this class of scenarios, however, the elastic scattering cross section of the twin tau with nuclei exceeds the bounds from XENONIT and other recent direct detection experiments. In this paper, we propose a modification to the fraternal twin Higgs scenario that we call Z(2)FTH, incorporating visible and twin hypercharged scalars (with Y = 2) which break twin electromagnetism. This leads to new mass terms for the twin tau that are unrelated to its Yukawa coupling, as well as additional annihilation channels via the massive twin photon. We show that these features make it possible for the right-handed twin tau to freeze out with an acceptable thermal relic abundance while scattering with nuclei at a rate that is well below existing constraints. Nonetheless, large portions of the currently viable parameter space in this model are within the reach of planned direct detection experiments. The prospects for indirect detection using gamma rays and cosmic-ray antiprotons are also promising in this model. Furthermore, if the twin neutrino is light, the predicted deviation of Delta N-eff approximate to 0.1 would be within reach of Stage 4 cosmic microwave background experiments. Finally, the high luminosity LHC should be able to probe the entire parameter space of the Z(2)FTH model through charged scalar searches. We also discuss how searches for long-lived particles are starting to constrain fraternal twin Higgs models.

Automated summary

This paper proposes a modification to the twin Higgs model, called Z(2)FTH, that can address the problem of the twin tau's elastic scattering cross section exceeding experimental bounds. The model incorporates visible and twin hypercharged scalars, which break twin electromagnetism and provide new annihilation channels. The model predicts an acceptable thermal relic abundance for the right-handed twin tau, and has potential for direct and indirect detection experiments as well as LHC searches.