Abstract
The nature of dark matter (DM) and how it might interact with the particles of the Standard Model (SM) is an ever-growing mystery. It is possible that the existence of new `dark sector' forces, yet undiscovered, are the key to solving this fundamental problem, and one might hope that in the future such forces might even be `unified' with the ones we already know in some UV-complete framework. In this paper, following a bottom-up approach, we attempt to take the first steps in the construction of such a framework. The much-discussed possibility of the kinetic mixing (KM) of the `dark photon' with the hypercharge gauge boson of the SM via loops of portal matter (PM) fields, charged in both sectors, offers an attractive starting point for these efforts. Given the anticipated finite strength of the KM in a UV-complete theory, the absence of anomalies, and the lifetime constraints on the PM fields arising from CMB and nucleosynthesis constraints, PM must behave as vector-like copies of the known SM fermion fields, such as those which appear naturally in $E_6$-type models. Within such a setup, the SM and their corresponding partner PM fields would be related by a new $SU(2)_I$ gauge symmetry. With this observation as a springboard, we construct a generalization of these ideas where $SU(2)_I$ is augmented by an additional $U(1)_{I_Y}$ factor so that the light dark photon is the result of a symmetry breaking analogous to the SM, \ie, $SU(2)_I\times U(1)_{I_Y}\to U(1)_D$, but with $U(1)_D$ now also broken at the $\lesssim$ GeV scale. While SM fields are $U(1)_D$ singlets, as in the conventional dark photon approach, they transform nontrivially under the full $SU(2)_I\times U(1)_{I_Y}$ gauge group. This approach leads to numerous interesting signatures, both at low energies and at colliders, and can be viewed as an initial step in the construction of a more UV-complete framework.
Highlights
The nature of dark matter (DM) is one of our biggest mysteries and points to there being new physics beyond the Standard Model (SM)
The favorite candidates for DM originated in top-down theories which addressed other outstanding problems within the SM such as axions [1,2] and weakly interacting massive particles (WIMPs) [3]
In I we argued that in a complete UV theory the strength of kinetic mixing (KM), ε, is a finite, in principle calculable, quantity as it is in grand unified theories (GUTs) [10] with split multiplets
Summary
The nature of dark matter (DM) is one of our biggest mysteries and points to there being new physics beyond the Standard Model (SM). There we briefly discussed the more complex, and perhaps much more interesting, possibility that portal matter may consist of a set of different vector-like fields with various SM quantum numbers whose infinite contributions to ε “naturally” cancel among themselves, as might be the case if they formed, e.g., a 5 þ 5 ̄ of SUð5Þ, as a potential way forward in constructing more realistic UVcomplete theories. This is the direction that we will follow in this paper. The last section summarizes our results and conclusions and points us in the direction of our steps
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