Searching for lepton flavor violating flavon decays at hadron colliders

Abstract

The search for flavons with a mass of $\mathcal{O}(1)\text{ }\text{ }\mathrm{TeV}$ at current and future colliders might probe low-scale flavor models. We are interested in the simplest model that invokes the Froggatt-Nielsen mechanism with an Abelian flavor symmetry, which includes a Higgs doublet and a Froggatt-Nielsen complex singlet. Assuming a $CP$ conserving scalar potential, there are a $CP$-even ${H}_{F}$ and a $CP$-odd ${A}_{F}$ flavons with lepton flavor violating (LFV) couplings. The former can mix with the standard-model-like Higgs boson, thereby inducing tree-level LFV Higgs interactions that may be at the reach of the LHC. We study the constraints on the parameter space of the model from low-energy LFV processes, which are then used to evaluate the flavon decay widths and the $gg\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\mu}$ ($\ensuremath{\phi}={H}_{F},{A}_{F}$) production cross section at hadron colliders. After imposing several kinematic cuts to reduce the standard model main background, we find that for ${m}_{{H}_{F}}$ about 200--350 GeV, the decay ${H}_{F}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\mu}$ might be at the reach of the LHC for a luminosity in the range $1--3\text{ }\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$, however, a luminosity of the order of $10\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$ would be required to detect the ${A}_{F}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\mu}$ decay. On the other hand, a future 100 TeV $pp$ collider could probe masses as high as $\mathcal{O}(10)\text{ }\text{ }\mathrm{TeV}$ if it reaches an integrated luminosity of at least $20\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$. Therefore, the 100 TeV Collider could work as a flavon factory.