The Physics of Heavy Z' Gauge Bosons

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 paper presents a theoretical framework for heavy Z' bosons emerging from additional U(1)' symmetries in extensions of the Standard Model.
• It employs anomaly-free and supersymmetric models to address issues like gauge group rank reduction and the SUSY μ problem.
• The study examines experimental constraints and predicts collider signatures, offering insights into new physics beyond the Standard Model.

The Physics of Heavy Z' Gauge Bosons

The paper discusses the theoretical framework and implications of hypothetical heavy $Z'$ gauge bosons associated with an additional $U(1)'$ gauge symmetry, extending the Standard Model (SM) of particle physics. The emergence of $Z'$ bosons is considered within various extensions to the SM, such as grand unified theories (GUTs), superstring theory, and supersymmetric models.

Key Concepts and Motivations

1. Additional Gauge Symmetries: The paper explores models with an extra $U(1)'$ symmetry, offering insights into breaking these symmetries and the possible mass scales of $Z'$ bosons. The motivation includes difficulties in reducing the rank of gauge groups, leading to preserved $U(1)$ factors.
2. Anomaly-Free Models: To ensure consistency, anomaly-free models are necessary. The paper considers classes of particle spectra that avoid anomalies. This typically requires the introduction of exotic particles, ensuring the model's theoretical consistency.
3. Supersymmetry and $Z'$ Implications: The presence of a $Z'$ could provide solutions to issues such as the SUSY $\mu$ problem. The $Z'$ might mediate supersymmetry breaking, leading to implications for the Higgs sector, neutralinos, and fermion masses.

Constraints and Experimental Prospects

• Current Experimental Constraints: The paper reviews constraints on $Z'$ bosons from electroweak precision measurements and collider experiments. It highlights the necessity to consider these constraints when framing theoretical models for new physics.
• Discovery Potential: The paper outlines the potential for $Z'$ discovery at future colliders, such as the LHC. Signatures of such particles include extended gauge structures and new interactions with known and exotic particles.

Implications and Future Directions

1. Theoretical Explorations: The $Z'$ bosons could lead to an extended Higgs sector and have implications for cosmology, such as contributions to dark matter and baryogenesis mechanisms.
2. Flavor Physics and Neutrino Masses: Models with $Z'$ bosons might address discrepancies in flavor-changing neutral currents and contribute to mechanisms generating neutrino masses.
3. Phenomenological Studies: Future efforts should focus on detailed calculations of $Z'$ production and decay channels to interpret experimental data consistently. This could include comprehensive studies on the interplay between theoretical models and observations.

In conclusion, the exploration of heavy $Z'$ gauge bosons via additional $U(1)'$ symmetries presents fertile ground for addressing outstanding questions in particle physics, potentially providing answers to phenomena not explained by the SM. The implications span both experimental and cosmological realms, necessitating continued research to elucidate the full scope of implications and observable signatures at current and future collider experiments.