Kinetic Mixing, Dark Higgs Triplets, $M_W$ and All That

Abstract: The kinetic mixing (KM) portal is a popular mechanism which allows light dark matter (DM) in the mass range below $\sim 1$ GeV to achieve the observed relic density by thermal means and can be effectively described by only a few parameters, e.g., $\epsilon$, the strength of this KM. In the simplest setup, the Standard Model (SM) $U(1)_Y$ hypercharge gauge boson and a $U(1)_D$ dark photon (DP), which only couples to fields in the dark sector, experience KM via loops of portal matter (PM) fields which have both SM and dark charges thus generating a small coupling between us and dark matter (DM). However, if one wishes to understand the underlying physics behind this idea in a deeper fashion we need to take a step upward to a more UV-complete picture. Meanwhile, CDFII has measured a value for the $W$-boson mass which lies significantly above SM expectations. In this paper we speculate that this shift in the $W$'s mass may be related to the $\sim 1$ GeV mass of the DP within a framework of scalar PM that leads to phenomenologically interesting values of $\epsilon$ via non-abelian KM due to the existence of an $SU(2)_L$, $Y=0$, {\it complex} Higgs triplet which carries a non-zero value of the $U(1)_D$ dark charge. Possible gauge boson plus missing energy signatures of this scenario that can appear at the LHC and elsewhere are examined. Indeed, with modest assumptions, all of the new scalar PM states are predicted to have masses below roughly $\simeq 630$ GeV and so should be at least kinematically accessible. The HL-LHC will very likely to be able to explore all of this model's allowed parameter space.