Overview of Axion-Like Particles at Future Colliders
The paper discusses axion-like particles (ALPs), which are pseudo Nambu-Goldstone bosons resulting from spontaneously broken global symmetries in extensions of the Standard Model (SM). ALPs are significant in theoretical physics due to their potential to address several open questions in the SM, including the strong CP problem. The authors explore various strategies to discover ALPs at future high-energy colliders, emphasizing the potential of these particles to indicate new physics sectors associated with large symmetry-breaking scales.
Key Contributions
- Collider Reach and Search Strategies: The paper extensively analyzes the reach of various proposed colliders, including future lepton and hadron colliders, for discovering ALPs. It investigates several production mechanisms such as resonant ALP production, production in the decay of heavy SM resonances, and associatively with photons, Z bosons, or Higgs bosons. The strategies accommodate both prompt and delayed ALP decays, demonstrating the wide range of parameter space that can be explored.
- Collider Projections: Detailed projections for the high-luminosity LHC and its high-energy upgrade, CLIC, CEPC, FCC-ee, SPPC, and FCC-hh are presented. These projections highlight the capability of each collider configuration to probe different regions of ALP parameter space, thereby advancing the case for varied collider designs to maximize discovery potential.
- Effective Lagrangian and Phenomenology: The paper utilizes an effective Lagrangian framework to describe ALP interactions with SM particles. It provides phenomenological insights, calculating branching ratios and decay widths for ALPs into different final states. The inclusion of loop-induced contributions ensures comprehensive coverage of ALP dynamics.
- Constraints from Electroweak Precision Measurements: Future measurements of electroweak precision parameters are posited to further constrain ALP couplings. This aspect highlights the multi-faceted approach required for ALP searches, integrating indirect constraints with direct collider experiments.
Numerical Results and Implications
The authors provide numerical results for ALP production cross-sections and decay rates, illustrating the sensitivity of different collider experiments to ALPs' mass and couplings. For instance, the projected reach of hadron colliders like FCC-hh and SPPC into previously inaccessible regions underscores the urgency for high-energy advancements. The analysis underscores the precision required to measure small couplings and light ALP masses, which are indicative of high symmetry-breaking scales.
By systematically outlining the prospects of ALPs at future colliders, the work serves as a pivotal reference for experimental designs and theoretical ambitions. While ALPs represent a broader class of potential new particles, their discovery would bear profound implications for our understanding of underlying symmetries and the nature of dark matter. Future directions may involve cross-disciplinary efforts, combining insights from astrophysical observations with collider experiments to probe deeper into the ALP landscape. The research signifies a strategic advancement in particle physics, paving the way for discoveries that extend beyond the Standard Model.