Abstract
We introduce a scenario for CP-violating (CPV) dark photon interactions in the context of non-abelian kinetic mixing. Assuming an effective field theory that extends the Standard Model (SM) field content with an additional $U(1)$ gauge boson ($X$) and a $SU(2)_L$ triplet scalar, we show that there exist both CP-conserving and CPV dimension five operators involving these new degrees of freedom and the SM $SU(2)_L$ gauge bosons. The former yields kinetic mixing between the $X$ and the neutral $SU(2)_L$ gauge boson (yielding the dark photon), while the latter induces CPV interactions of the dark photon with the SM particles. We discuss experimental probes of these interactions using searches for permanent electric dipole moments (EDMs) and di-jet correlations in high-energy $pp$ collisions. It is found that the experimental limit on the electron EDM currently gives the strongest restriction on the CPV interaction. In principle, high energy $pp$ collisions provide a complementary probe through azimuthal angular correlations of the two forward tagging jets in vector boson fusion. In practice, observation of the associated CPV asymmetry is likely to be challenging.
Highlights
In recent years, the possible existence of a new Uð1Þ gauge boson has been motivated by experimental results in several phenomenological contexts, such as lepton flavor universalities in B physics [1,2,3,4,5] and muon anomalous magnetic moment [2,6,7]
The dark photon (X) has kinetic mixing with the Standard Model (SM) Uð1ÞY gauge boson, XμνBμν, yielding interactions with the SM particles [10,11] parametrized by a dimensionless parameter ε
The dark photon is a new Uð1Þ gauge boson, which is motivated by several phenomenological considerations
Summary
The possible existence of a new Uð1Þ gauge boson has been motivated by experimental results in several phenomenological contexts, such as lepton flavor universalities in B physics [1,2,3,4,5] and muon anomalous magnetic moment [2,6,7]. Once we have addressed the small kinetic mixing parameter ε with the dimension-5 CP-conserving (CPC) operator, it is well motivated and natural to investigate possible CPV interactions. One may ask about the possibility of CP-violating (CPV) kinetic mixing, BμνXμν with Xμν 1⁄4 εμναβXαβ=2 It is not present since the interaction is equivalent to total derivative and does not contribute to the action. We expect that the collider signature of the CPV interactions is potentially observable, having no suppression associated with a small scalar mixing term. We will illustrate how the fermion EDMs probe the CPV dimension-5 operator of a massive dark photon and discuss the possibility of the complementary probe at the Large Hadron Collider (LHC).
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