Electroweak Limits on General New Vector Bosons

TL;DR

The paper develops a gauge‑invariant, model‑independent framework to study general heavy spin‑1 vector bosons by matching to a dimension‑six effective Lagrangian and constraining it with EWPD and LEP2 data. It classifies 15 SM gauge representations, derives the corresponding operator coefficients, and performs EWPD fits for each vector type, including single‑vector and multi‑vector scenarios, with both universal and nonuniversal fermion couplings. The results show that many vectors are tightly constrained in their leptonic couplings, while multi‑vector setups can alleviate or modify bounds via cancellations and can even accommodate a heavier Higgs mass under certain conditions. The analysis provides guidance for model building and collider searches (Tevatron/LHC) and clarifies how nonuniversal couplings, especially in the bottom sector, can address observed anomalies like A_FB^b, within perturbativity limits. Overall, the work offers a comprehensive framework to assess the electroweak viability of broad classes of new vector bosons and their implications for Higgs physics and collider phenomenology.

Abstract

We study extensions of the Standard Model with general new vector bosons. The full Standard Model gauge symmetry is used to classify the extra vectors and constrain their couplings. We derive the corresponding effective Lagrangian, valid at energies lower than the mass of the extra vectors, and use it to extract limits from electroweak precision observables, including LEP 2 data. We consider both universal and nonuniversal couplings to fermions. We study the interplay of several extra vectors, which can have the effect of opening new regions in parameter space. In particular, it allows to explain the anomaly in the bottom forward-backward asymmetry with perturbative couplings. Finally, we analyze quantitatively the implications for the Higgs mass.

Figures (9)

• Figure 1: Feynman diagrams relevant for the dimension-six effective Lagrangian.
• Figure 2: From darker to lighter, confidence regions with $\Delta \chi^2\leq$$2$ (blue), $4$ (orange) and $6$ ($95\%$ C.L.) (green), respectively, for the ${\cal B}$ couplings to leptons assuming no couplings to quarks. The region in the left plot results from the fit to EWPD without LEP 2 data. This is further constrained into the smaller region in the right plot by adding the LEP 2 cross sections and asymmetries to the fit.
• Figure 3: From darker to lighter, confidence regions with $\Delta \chi^2\leq$$2$(blue), $4$ (orange) and $6$ ($95\%$ C.L.) (green), respectively, for the ${\cal B}$ couplings to the Higgs and LH leptons assuming no couplings to quarks. The regions in the plot on the left are obtained from a fit to EWPD without LEP 2 data. They are reduced to smaller regions when the LEP 2 cross sections and asymmetries are added to the fit, as shown in the plot on the right.
• Figure 4: $95\%$ C.L. contour in the $M_{Z^\prime}$ - $\sin{\theta_{Z{Z^\prime}}}$ plane for the $Z^\prime_{R}$ model (left) and $Z^\prime_\psi$ (right). The different contours correspond to the fit to EWPD without LEP 2 cross sections and asymmetries (solid line), to LEP 2 cross sections and asymmetries (dashed line), and to all data (solid region).
• Figure 5: From darker to lighter, confidence regions with $\Delta \chi^2\leq$$2$ (blue), $4$ (orange) and $6$ ($95\%$ C.L.) (green), respectively, for the ${\cal W}$ couplings to LH leptons and to the Higgs boson. Notice the flat direction along the Higgs coupling axis when the lepton charge vanishes.