Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

The Physics of Heavy Z' Gauge Bosons

Paul Langacker

TL;DR

Heavy Z' gauge bosons arise naturally in extensions of the Standard Model with extra U(1)' factors, often tied to grand unification or string theories. The paper surveys the theoretical landscape, detailing Z' couplings, mass mixing, anomaly cancellation (frequently requiring exotics), and kinetic mixing, along with SUSY-specific issues like the μ problem and the extended Higgs/neutralino sectors. It classifies canonical and non-canonical models (including E6-based, LR, Little Higgs/extra-dimensions/strong-dynamics scenarios) and discusses mass scales from massless to TeV-scale Z' with secluded sectors. On the experimental side, it reviews precision electroweak constraints and collider searches, and outlines diagnostics to extract Z' couplings, spins, and potential signals of exotics or hidden sectors. The work emphasizes the broad phenomenological reach of a Z', including implications for neutrino mass, dark matter, baryogenesis, FCNCs, and possible SUSY-breaking mediation, underscoring the transformative potential of discovering a Z' at the LHC, ILC, or future facilities.

Abstract

The U(1)' symmetry associated with a possible heavy Z' would have profound implications for particle physics and cosmology. The motivations for such particles in various extensions of the standard model, possible ranges for their masses and couplings, and classes of anomaly-free models are discussed. Present limits from electroweak and collider experiments are briefly surveyed, as are prospects for discovery and diagnostic study at future colliders. Implications of a Z' are discussed, including an extended Higgs sector, extended neutralino sector, and solution to the mu problem in supersymmetry; exotic fermions needed for anomaly cancellation; possible flavor changing neutral current effects; neutrino mass; possible Z' mediation of supersymmetry breaking; and cosmological implications for cold dark matter and electroweak baryogenesis.

The Physics of Heavy Z' Gauge Bosons

TL;DR

Heavy Z' gauge bosons arise naturally in extensions of the Standard Model with extra U(1)' factors, often tied to grand unification or string theories. The paper surveys the theoretical landscape, detailing Z' couplings, mass mixing, anomaly cancellation (frequently requiring exotics), and kinetic mixing, along with SUSY-specific issues like the μ problem and the extended Higgs/neutralino sectors. It classifies canonical and non-canonical models (including E6-based, LR, Little Higgs/extra-dimensions/strong-dynamics scenarios) and discusses mass scales from massless to TeV-scale Z' with secluded sectors. On the experimental side, it reviews precision electroweak constraints and collider searches, and outlines diagnostics to extract Z' couplings, spins, and potential signals of exotics or hidden sectors. The work emphasizes the broad phenomenological reach of a Z', including implications for neutrino mass, dark matter, baryogenesis, FCNCs, and possible SUSY-breaking mediation, underscoring the transformative potential of discovering a Z' at the LHC, ILC, or future facilities.

Abstract

The U(1)' symmetry associated with a possible heavy Z' would have profound implications for particle physics and cosmology. The motivations for such particles in various extensions of the standard model, possible ranges for their masses and couplings, and classes of anomaly-free models are discussed. Present limits from electroweak and collider experiments are briefly surveyed, as are prospects for discovery and diagnostic study at future colliders. Implications of a Z' are discussed, including an extended Higgs sector, extended neutralino sector, and solution to the mu problem in supersymmetry; exotic fermions needed for anomaly cancellation; possible flavor changing neutral current effects; neutrino mass; possible Z' mediation of supersymmetry breaking; and cosmological implications for cold dark matter and electroweak baryogenesis.

Paper Structure

This paper contains 56 sections, 83 equations, 2 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Basic Issues
  3. $Z'$ Couplings
  4. Masses and Mass Mixings
  5. Anomalies and Exotics
  6. Kinetic Mixing
  7. One and Two Higgs Doublets, Supersymmetry, and the $\mu$ Problem
  8. Higgs Doublets
  9. Non-Holomorphic Terms
  10. The $\mu$ Problem
  11. Models
  12. Canonical Examples
  13. The sequential model
  14. Models based on $T_{3R}$ and $B - L$
  15. The $E_6$ models
  16. ...and 41 more sections

Figures (2)

  • Figure 1: Limits on the $Z'$ mass $M_2$ and the $Z-Z'$ mixing angle $\theta$ for the $\chi$, $\psi$, $\eta$, and $LR\ (\alpha=1.53)$ models. The solid (dashed) contours are 90% cl exclusions from precision electroweak data for $\rho_0=1\ (\rho_0 ={\rm\ free})$. A cross, $x$, is the best fit. The horizontal solid line is the 95% cl Tevatron lower limit, assuming decays into SM particles only. The horizontal dotted line is the 95% cl lower limit from LEP 2. The contours marked $0, 1, 5, \infty$ are for various theoretical relations between the mass and mixing and are defined in the text. Updated from Erler:1999ub.
  • Figure 2: Discovery limits for an $E_6$$Z'$ as a function of $\theta\equiv\theta_{E_6}$ corresponding to a total of 10 $e^+e^-$ or $\mu^+\mu^-$ events using $\sigma_{Z'}$ from Eq. \ref{['cros']}. In each panel the top two curves assume decays into SM fermions only, while the bottom two assume that decays into exotics and sparticles are unsuppressed. The different shapes of the Tevatron and LHC curves is because the $u$ quark dominates at the Tevatron, while the $u$ and $d$ are more comparable at the LHC. From Kang:2004bz.