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Model Independent Bounds on Kinetic Mixing

Anson Hook, Eder Izaguirre, Jay G. Wacker

TL;DR

This work derives model-independent bounds on kinetic mixing between the Standard Model hypercharge and a new Abelian vector boson $A'$ with mass in the range $1\,\mathrm{GeV}$ to $1\,\mathrm{TeV}$ by examining virtual $A'$ effects on precision electroweak observables. It employs a tree-level, full-model calculation of deviations and performs a global $\chi^2$ fit to SM parameters using data from $e^+e^-$ experiments, including the $Z^0$ mass, differential Bhabha scattering, forward-backward asymmetries, and hadronic cross sections. The main result is a model-independent upper bound of $\epsilon \lesssim 0.03$ over most of the mass range, with nuances near the $Z^0$ pole and around collider energies where resonant production can occur; while some parameter space remains for dark-sector interactions, these limits constrain a broad class of kinetically mixed scenarios and motivate future high-intensity $e^+e^-$ and LHC studies. The approach provides robust constraints that do not rely on specific dark-sector decay channels, highlighting the continued value of precision SM measurements for uncovering hidden new physics.

Abstract

New Abelian vector bosons can kinetically mix with the hypercharge gauge boson of the Standard Model. This letter computes the model independent limits on vector bosons with masses from 1 GeV to 1 TeV. The limits arise from the numerous e+e- experiments that have been performed in this energy range and bound the kinetic mixing by epsilon < 0.03 for most of the mass range studied, regardless of any additional interactions that the new vector boson may have.

Model Independent Bounds on Kinetic Mixing

TL;DR

This work derives model-independent bounds on kinetic mixing between the Standard Model hypercharge and a new Abelian vector boson with mass in the range to by examining virtual effects on precision electroweak observables. It employs a tree-level, full-model calculation of deviations and performs a global fit to SM parameters using data from experiments, including the mass, differential Bhabha scattering, forward-backward asymmetries, and hadronic cross sections. The main result is a model-independent upper bound of over most of the mass range, with nuances near the pole and around collider energies where resonant production can occur; while some parameter space remains for dark-sector interactions, these limits constrain a broad class of kinetically mixed scenarios and motivate future high-intensity and LHC studies. The approach provides robust constraints that do not rely on specific dark-sector decay channels, highlighting the continued value of precision SM measurements for uncovering hidden new physics.

Abstract

New Abelian vector bosons can kinetically mix with the hypercharge gauge boson of the Standard Model. This letter computes the model independent limits on vector bosons with masses from 1 GeV to 1 TeV. The limits arise from the numerous e+e- experiments that have been performed in this energy range and bound the kinetic mixing by epsilon < 0.03 for most of the mass range studied, regardless of any additional interactions that the new vector boson may have.

Paper Structure

This paper contains 3 sections, 18 equations, 2 figures.

Table of Contents

  1. Kinetic Mixing
  2. Precision SM Measurements
  3. Results

Figures (2)

  • Figure 1: The model independent upper bounds on $\Gamma_{Z'}$ arising from the line shape of the $Z^0$.
  • Figure 2: 95% CL exclusions in the $(m_{Z'},\epsilon)$. The cyan region is excluded for a "wide" $Z'$ and the purple region is for a "narrow" $Z'$. The blue region shows the bounds placed by CDF on direct production of $Z'$s. The inset illustrates the constraints on $m_{Z'}$ near the $Z^0$ pole. The bound from the $(g-2)_\mu$ is shown in dark grey and the light grey, dashed region shows the sensitivity from model dependent BaBar searches.