# Muon specific two-Higgs-doublet model

## TL;DR

This paper proposes a new two-Higgs-doublet model with a specific symmetry to explain the muon g-2 anomaly, successfully fitting experimental data within the 1σ level while satisfying multiple theoretical and experimental constraints.

## Contribution

It introduces a muon-specific two-Higgs-doublet model with a softly-broken Z4 symmetry, enhancing muon couplings and avoiding previous constraints, thus explaining muon g-2 within 1σ.

## Key findings

- Model explains muon g-2 within 1σ
- Avoids constraints from leptonic τ decays
- Satisfies unitarity, stability, and LHC data

## Abstract

We investigate a new type of a two-Higgs-doublet model as a solution of the muon $g-2$ anomaly. We impose a softly-broken $Z_4$ symmetry to forbid tree level flavor changing neutral currents in a natural way. This $Z_4$ symmetry restricts the structure of Yukawa couplings. As a result, extra Higgs boson couplings to muons are enhanced by a factor of $\tan\beta$, while their couplings to all the other standard model fermions are suppressed by $\cot\beta$. Thanks to this coupling property, we can avoid the constraint from leptonic $\tau$ decays in contrast to the lepton specific two-Higgs-doublet model, which can explain the muon $g-2$ within the 2$\sigma$ level but cannot within the $1\sigma$ level due to this constraint. We find that the model can explain the muon $g-2$ within the 1$\sigma$ level satisfying constraints from perturbative unitarity, vacuum stability, electroweak precision measurements, and current LHC data.