Dark-photon searches via $ZH$ production at $e^+e^-$ colliders

Understand

We study the $ZH$ associated production followed by the Higgs $H\to \gamma \bar{\gamma}$ decay into a photon plus an invisible and massless dark photon, at future high-energy $e^+e^-$ facilities.

• Large $H\to \gamma \bar{\gamma}$ decay rates (with branching ratios up to a few percent) are allowed, thanks to possible non-decoupling properties of the Higgs boson under specific conditions, and unsuppressed dark-photon couplings in the dark sector.
• Such large decay rates can be obtained in the framework of recent flavor models that aim to naturally explain the observed spread in the fermion mass spectrum.
• We analyze the experimental prospects for observing the $e^+e^-\rightarrow ZH$ process followed by the semi invisible Higgs decay into a photon plus a massless invisible system.