Tera-Zooming in on light (composite) axion-like particles

TL;DR

The paper demonstrates that future Tera-Z colliders can significantly advance the search for axion-like particles, probing high energy scales and constraining models related to the muon g-2 anomaly beyond current experiments.

Contribution

It introduces the potential of Tera-Z colliders to explore ALPs produced via Z decays, extending sensitivity to composite scales up to hundreds of TeV, surpassing existing collider capabilities.

Findings

Tera-Z can probe composite scales up to hundreds of TeV.

The results constrain models explaining the muon g-2 anomaly.

The study applies to both photophilic and photophobic ALPs.

Abstract

The Tera-Z phase of future $e^+ e^-$ colliders, FCC-ee and CepC, is a goldmine for exploring $Z$ portal physics. We focus on axion-like particles (ALPs) that can be produced via $Z$ decays with a monochromatic photon. As a template model, we consider composite Higgs models with a light pseudo-scalar that couples through the Wess-Zumino-Witten term to the electroweak gauge bosons. For both photophilic and photophobic cases, we show that the Tera-Z can probe composite scales up to $100$s of TeV, well beyond the capability of the LHC and current precision physics. Our results also apply to generic ALPs and, in particular, severely constrain models that explain the muon $g-2$ anomaly.