Fourth generation leptons and muong−2

Abstract

We consider the contributions to ${g}_{\ensuremath{\mu}}\ensuremath{-}2$ from fourth generation heavy neutral and charged leptons $N$ and $E$, respectively, at the one-loop level. Diagrammatically, there are two types of contributions: boson-boson-$N$ and $E\ensuremath{-}E$-boson in the loop diagram. In general, the effect from $N$ is suppressed by off-diagonal lepton mixing matrix elements. For $E$, we consider flavor changing neutral couplings arising from various new physics models, which are stringently constrained by $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$. We assess how the existence of a fourth generation would affect these new physics models.