The BSM potential of Momentum-dependent Widths and Propagators

Incorporating self-energy corrections via Dyson resummation can quantify the deviations from the fixed-width approximation, to an extent such that one can assess their implications on the myriad of collider observables. This proceeding highlights the BSM reach of momentum-dependent particle widths and propagators of gauge and Higgs bosons, and the top quark using the SMEFT framework. While effects on the Higgs boson are negligible and the $W$ boson shows percent-level deviations in reconstructed transverse mass distributions, the top quark exhibits significant sensitivity near its mass threshold. Future lepton colliders, e.g., electron-positron machines or muon colliders, can offer sensitivity to these effects, enabling a novel avenue of constraining SMEFT Wilson coefficients. Momentum dependencies can indeed provide additional sensitivity at precision-era experiments, enhancing the potential for discovering new physics there.