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 ∼ 1 GeV to achieve the observed relic density by thermal means and can be effectively described by only a few parameters, e.g., , 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 ∼ 1 GeV mass of the DP within a framework of scalar PM that leads to phenomenologically interesting values of via non-abelian KM due to the existence of an SU (2)L, Y = 0, 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 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.

A Consistent Theory of Kinetic Mixing and the Higgs Low-Energy Theorem

“…Note that a similar operator is present in models in which the SM is extended by an SU (2) L triplet scalar[29,33,34].…”

“…In this Letter we calculate the contributions from mixing between the X and the neutral SU (2) L gauge boson in a general form, which apart from few exceptions [28,29] have been neglected or omitted in the literature, and derive consistent expressions at the tree and loop level. We further use these expressions to provide the first formulation of low-energy theorems for Higgs couplings with the X boson that are relevant for Higgs decays in any theory involving kinetic mixing.…”

Lepton Flavor Portal Matter

“…As noted by Holdom [14,15], finite and calculable kinetic mixing of this magnitude can be generated at one loop if there exist additional fields in the theory which are charged under both U (1) D and U (1) Y , and the U (1) D and U (1) Y charges of the additional fields are such that the ultraviolet divergence from each field's loop contribution is cancelled by the others. Recently there has been interest in the theory and phenomenology of these "portal matter" fields [21][22][23][24][25][26][27][28][29][30][31], in scenarios in which they are light enough to be kinematically accessible at present or near-future experiments. It was noted in [21] that if the portal matter is fermionic, the most phenomenologically viable scenario would be for the portal matter to be charged under U (1) D , have identical SM quantum numbers to some SM field, and be vector-like under the SM gauge group and U (1) D .…”

“…Such fields have distinctive experimental signatures in collider experiments [32,33], dominantly decaying into highly boosted jets (for QCD-charged portal matter) or leptons (for leptonic portal matter), plus a dark photon or dark Higgs, in contrast to channels featuring the emission of an electroweak boson that dominate vector-like fermion decay widths in scenarios without the U (1) D symmetry. Furthermore, these new portal matter fields may play a role in a variety of other unresolved questions in physics, such as the recently-observed W mass anomaly [27,34].…”

“…In all of our subsequent computations in this work, we shall employ the parameterization of Eqs. (26)(27)(28) to specify points in parameter space of this model.…”