LAUSR

We study the contributions of colorless vectorlike fermions to the triple gauge couplings ${W}^{+}{W}^{\ensuremath{-}}\ensuremath{\gamma}$ and ${W}^{+}{W}^{\ensuremath{-}}{Z}^{0}$. We consider models in which their coupling to the Standard Model Higgs boson is allowed or forbidden by quantum numbers. We assess the sensitivity of the future accelerators FCC-ee, ILC, and CLIC to the parameters of these models, assuming they will be able to constrain the anomalous triple gauge couplings with precision $\ensuremath{\delta}{\ensuremath{\kappa}}_{V}\ensuremath{\sim}\mathcal{O}({10}^{\ensuremath{-}4})$, $V=\ensuremath{\gamma},{Z}^{0}$. We show that the combination of measurements at different center-of-mass energies helps to improve the sensitivity to the contribution of vectorlike fermions, in particular when they couple to the Higgs. In fact, the measurements at the FCC-ee and, especially, the ILC and the CLIC, may turn the triple gauge couplings into a new set of precision parameters able to constrain the models better than the oblique parameters or the $H\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ decay, even assuming the considerable improvement of the latter measurements achievable at the new machines.