Heavy Higgsino Dark Matter at the Scale of the Vanishing Higgs Quartic

Abstract

The Standard Model Higgs quartic coupling runs to zero around $10^9-10^{12}$ GeV at $2\sigma$, suggestive of an ultraviolet boundary condition $\lambda\simeq0$ at this scale. In a well-motivated class of high-scale supersymmetric (SUSY) models, the quartic is automatically set to zero at tree level at the superpartner scale. The Higgsino can naturally emerge as the lightest SUSY particle, with its two neutral Weyl components sufficiently degenerate to form an effectively Dirac fermion with an unsuppressed vector coupling to the $Z$. For such Higgsino dark matter, direct detection requires a mass above $\sim10^{11}$ GeV, leading to a coincidence with the scale independently selected by the vanishing quartic. Such a heavy Higgsino cannot freeze out with the observed relic density. However, if its mass exceeds the reheating temperature, the observed dark matter abundance can be reproduced through Boltzmann suppressed freeze-in. This scenario connects the dark matter mass to the measured Higgs mass, with a parameter space already constrained by LUX-ZEPLIN (LZ) and which will be decisively tested at DARWIN/XLZD. Finally, we consider PeV Higgsinos with Majorana gauginos of order $10^7$ GeV, permitting an inelastic Higgsino interpretation of the tentative LZ event while retaining the connection between the scalar superpartner scale and the vanishing Higgs quartic scale.