Speaker
Description
New U(1) gauge theories involving Standard Model (SM) fermions typically require additional electroweak fermions for anomaly cancellation. We study the non-decoupling properties of these new fermions, called anomalons, in the Z−Z′−γ vertex function, reviewing the connection between the full model and the effective Wess-Zumino operator. We calculate the exotic Z→Z′γ decay width in U(1)B−L and U(1)B models, where B and L denote the SM baryon and lepton number symmetries. For U(1)B−L gauge symmetry, each generation of SM fermions is anomaly free and the exotic Z→Z′BLγ decay width is entirely induced by intragenerational mass splittings. In contrast, for U(1)B gauge symmetry, the existence of two distinct sources of chiral symmetry breaking enables a heavy, anomaly-free set of fermions to have an irreducible contribution to the Z→Z′Bγ decay width. We show that the current LEP limits on the exotic Z→Z′Bγ decay are weaker than previously estimated, and low-mass Z′B dijet resonance searches are currently more constraining. We present a summary of the current collider bounds on U(1)B and a projection for a TeraZ factory on the Z→Z′Bγ exotic decay, and emphasize how the Z→Z′γ decay is emblematic of new anomalous U(1) gauge symmetries.
