Fourth Generation Leptons and Muon $g-2$

Understand

We consider the contributions to $g_\mu-2$ from fourth generation heavy neutral and charged leptons, $N$ and $E$, at the one-loop level.

• Diagrammatically, there are two types of contributions: boson-boson-$N$, and $E$-$E$-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 $\mu\to e\gamma$.