Constraining the heavy leptophilic neutral gauge bosons through the $Z\to\ell^+\ell^-$, $W^\pm\to\ell^\pm\nu_\ell$, and $h\to\ell^+\ell^-$ decays
We consider the hypothetical possibility of neutral gauge bosons ($Z^\prime$) with flavor-specific leptophilic couplings. For such New Physics (NP) interactions, the current experimental constraints are much relaxed in the heavy mass regime, particularly for masses $\geq \mathcal{O}(1)$ TeV. However, in the presence of a leptophilic $Z^\prime$, leptonic decay modes of the electroweak gauge bosons and Higgs can be corrected at the loop level. Using the existing upper bounds on the corresponding decay widths, we find that one can impose stronger exclusion limits on the interactions of a heavy $Z^\prime$. Future updates on the aforesaid decay channels can be used in complementarity with the proposed lepton colliders to probe even weaker leptophilic NP interactions at the TeV scale and beyond.