Light flavon signals at electron - photon colliders

TL;DR

This paper explores the potential for electron-photon colliders to detect light flavons around 100 GeV, which are predicted by certain flavor symmetry models, through specific lepton final states with suppressed backgrounds.

Contribution

It demonstrates that electron-photon colliders can effectively search for light flavons predicted by A4 flavor symmetry models, providing a new collider-based detection method.

Findings

Electron-photon collisions can produce flavons via $e^-\gamma o l^- T$.

Flavor-conserving and violating final states can be distinguished with invariant mass cuts.

Significant discovery potential exists even for flavon masses above flavor physics limits.

Abstract

Flavor symmetries are useful to realize fermion flavor structures in the standard model. In particular, discrete $A_4$ symmetry is used to realize lepton flavor structures, and some scalars which are called flavon are introduced to break this symmetry. In many models, flavons are assumed to be much heavier than the electroweak scale. However, our previous work showed that flavon mass around 100 GeV is allowed by experimental constraints in the $A_4$ symmetric model with residual $Z_3$ symmetry. In this paper, we discuss collider search of such a light flavon $\varphi_T$. We find that an electron - photon collision, as a considerable option at the international linear collider, has advantages to search for the signals. At the electron - photon collider flavons are produced as $e^-\gamma \to l^- \varphi_T$ and decay into two charged leptons. Then we analyze signals of flavor-conserving final-state $\tau^+ \tau^- e^-$, and flavor-violating final-states $\tau^+ \mu^- \mu^-$ and $\mu^+ \tau^- \tau^-$ by carrying out numerical simulation. For the former final-state, SM background can be strongly suppressed by imposing cuts on the invariant masses of final-state leptons. For the later final-states, SM background is extremely small, because in the SM there are no such flavor-violating final-states. We then find that sufficient discovery significance can be obtained, even if flavons are heavier than the lower limits from flavor physics.