Leptophilic U(1) Massive Vector Bosons from Large Extra Dimensions: Reexamination of Constraints from LEP Data

TL;DR

This paper reexamines constraints on leptophilic U(1) vector bosons from LEP data, showing that lighter KK modes could still explain the muon g-2 anomaly despite stricter bounds, with implications for extra-dimensional models.

Contribution

It provides a revised analysis of LEP constraints on KK excitations, demonstrating the viability of light KK modes explaining muon g-2 discrepancy within extra-dimensional frameworks.

Findings

Stricter bounds on KK masses and couplings from electroweak data.

Light KK modes (around 60 GeV) can still account for muon g-2.

The model suggests a string scale of about 10 TeV with small gauge coupling.

Abstract

Very recently, we proposed an explanation of the discrepancy between the measured anomalous magnetic moment of the muon and the Standard Model (SM) prediction in which the dominant contribution to $(g-2)_\mu$ originates in Kaluza-Klein (KK) excitations (of the lepton gauge boson) which do not mix with quarks (to lowest order) and therefore can be quite light avoiding LHC constraints. In this addendum we reexamine the bounds on 4-fermion contact interactions from precise electroweak measurements and show that the constraints on KK masses and couplings are more severe than earlier thought. However, we demonstrate that our explanation remains plausible if a few KK modes are lighter than LEP energy, because if this were the case the contribution to the 4-fermion scattering from the internal propagator would be dominated by the energy and not by the mass. To accommodate the $(g-2)_\mu$ discrepancy we assume that the lepton number $L$ does not partake in the hypercharge and propagates in one extra dimension (transverse to the SM branes): for a mass of the lowest KK excitation of 60 GeV (lower than the LEP energy), the string scale is roughly 10 TeV while the $L$ gauge coupling is of order $\sim 10^{-1}$.