Muon g-2 and lepton flavor violation in a two Higgs doublets model for the fourth generation

TL;DR

This paper proposes a two Higgs doublet model for the fourth generation that can explain the muon g-2 anomaly through heavy neutrino loops, and explores related lepton flavor violation and rare decay processes.

Contribution

It introduces a 2HDM tailored for the 4th generation, showing how heavy neutrino loops can account for the muon g-2 discrepancy, unlike previous models.

Findings

Heavy neutrino loops explain muon g-2 in the 4G2HDM.

Lepton flavor violating decays are sensitive to new couplings.

Predictions for rare decays like B_s → μμ are discussed.

Abstract

In the minimal Standard Model (SM) with four generations (the so called SM4) and in "standard" two Higgs doublets model (2HDM) setups, e.g., the type II 2HDM with four fermion generations, the contribution of the 4th family heavy leptons to the muon magnetic moment is suppressed and cannot accommodate the measured $ \sim 3 \sigma$ access with respect to the SM prediction. We show that in a 2HDM for the 4th generation (the 4G2HDM), which we view as a low energy effective theory for dynamical electroweak symmetry breaking, with one of the Higgs doublets coupling only to the 4th family leptons and quarks (thus effectively addressing their large masses), the loop exchanges of the heavy 4th generation neutrino can account for the measured value of the muon anomalous magnetic moment. We also discuss the sensitivity of the lepton flavor violating decays $\mu \to e \gamma$ and $\tau \to \mu \gamma$ and of the decay $B_s \to \mu \mu$ to the new couplings which control the muon g-2 in our model.