Exploring fermionic dark matter via Higgs boson precision measurements at the Circular Electron Positron Collider

Abstract

We study the impact of fermionic dark matter (DM) on projected Higgs precision measurements at the Circular Electron Positron Collider (CEPC), including the one-loop effects on the e þ e − → Zh cross section and the Higgs boson diphoton decay, as well as the tree-level effects on the Higgs boson invisible decay. As illuminating examples, we discuss two UV-complete DM models, whose dark sector contains electroweak multiplets that interact with the Higgs boson via Yukawa couplings. The CEPC sensitivity to these models and current constraints from DM detection and collider experiments are investigated. We find that there exist some parameter regions where the Higgs measurements at the CEPC will be complementary to current DM searches.

Virtual signatures of dark sectors in Higgs couplings

“…Scenario 2 is thus much better protected from direct detection bounds than scenario 1. For χ 0 2 to be a thermal relic, strong co-annihilation with the nearly-degenerate charged states χ ± requires the mass spectrum of dark fermions to be around the TeV scale [10,21]. In section VII, we will come back to a possible dark matter interpretation of our results.…”

“…Dark fermion effects in Higgs-Z boson associated production at future lepton colliders have also been studied in refs. [9,10]. Establishing indirect evidence of dark fermions will crucially depend on the achievable precision in Higgs coupling measurements.…”

“…Collider searches for virtual effects of dark matter have recently been explored for instance in refs. [8][9][10][11][12].…”

The minimal fermionic model of electroweak baryogenesis

“…The singlet-doublet model has also been studied in the literature mostly in the context of dark matter [29][30][31][32]37], but we point out that since in fermion induced EWBG the new fermions must couple strongly to the Higgs, the lightest singlet-doublet fermion would be ruled out as a dark matter candidate from direct detection experiments. Generically, if the relic density of singlet-doublet fermions is large, direct detection experiments severely constrain the model.…”

“…Along this direction (or more generally, along the λ u = λ d direction if we also allow for a physical CP violating phase), the singletdoublet sector has an enhanced SU(2) R custodial symmetry which ensures a vanishing T parameter [29,30,[35][36][37]. In spite of this, from the figure we see that for the order one Yukawas and non-decoupled singlet-doublet fermions needed for the strong first order phase transition, the λ u = λ d direction is generically excluded, mostly due to a large S parameter.…”