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.
Highlights
The standard model (SM) particles were completed with the discovery of the Higgs boson
We analyze signals of the flavor-conserving final state τþτ−e− and the flavor-violating final states τþμ−μ− and μþτ−τ− by carrying out numerical simulations. For the former final state, SM background can be strongly suppressed by imposing cuts on the invariant masses of final-state leptons
We find that sufficient discovery significance can be obtained, even if flavons are heavier than the lower limits from flavor physics
Summary
The standard model (SM) particles were completed with the discovery of the Higgs boson. In order to explain large lepton mixing angles, many authors have studied the lepton flavor structure by using non-Abelian discrete symmetries as a flavor symmetry [12], the authors predicted the nonzero reactor angle with broken TBM by adding an extra flavon to the AF model. [13,14,15,16], the authors discussed the mass restriction on the flavons which mix with the SM Higgs, from lepton flavor violation (LFV) and collider physics. We find that an electron-photon collider has many advantages for searching for flavon signals.
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