Abstract
A new U(1)X gauge boson field X can have renormalizable kinetic mixing with the standard model (SM) U(1)Y gauge boson field Y. This mixing induces interactions of X with SM particles even though X starts as a dark photon without such interactions. If the U(1)X is not broken, both the dark photon field X and the photon field A are massless. One cannot determine which one of them is the physical dark photon or the photon by just looking at kinetic terms in the Lagrangian. We revisit this issue and show explicitly that when all contributions are included, all physical processes do not depend on which basis is used and the kinetic mixing effects do not show up in electromagnetic and weak interactions if only SM particles are involved in the calculations. On the other hand, the kinetic mixing provides a portal for probing the dark sector beyond the SM. We update constraints on the millicharged dark sector particles from the Lamb shift and lepton g−2 measurements.
Highlights
One cannot determine which one of them is the physical dark photon or the photon by just looking at kinetic terms in the Lagrangian. We revisit this issue and show explicitly that when all contributions are included, all physical processes do not depend on which basis is used and the kinetic mixing effects do not show up in electromagnetic and weak interactions if only standard model (SM) particles are involved in the calculations
A new gauge symmetry U (1)X with a gauge boson field X can mix with the U (1)Y gauge boson field Y of U (1)Y in the standard model (SM) through a renormalizable kinetic mixing operator XμνY μν formed by the field strengths, Fμν = ∂μFν − ∂νFμ, with F = X, Y [1,2,3,4]
We show that for the SM extended with a U (1)X gauge field having kinetic mixing with SM U (1)Y gauge field, the physical massless dark photon cannot be distinguished from the photon if re-writing gauge fields in the canonical form is the only requirement for removing the kinetic mixing term in the case with mX = 0
Summary
If the SM particles are all uncharged under the U (1)X, it is expected to have no interaction with SM particles In this case X is dubbed as a dark photon field. The kinetic mixing term can induce interactions between X and the SM particles This has many interesting consequences in low energy and high energy phenomena from particle physics, astrophysics to cosmology perspectives. The angle that describes the general orthogonal transformation does not affect how the massless dark photon and photon interact with SM particles. We show that effects of the kinetic mixing does not leave traces in the electromagnetic (EM) and weak interactions involving only SM particles (in loops or external states), such as g − 2 of a charged lepton and in the processes Higgs decays into two photons, and Z boson decays into SM particles.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
