We present the first calculation of the one-loop corrections to the triple Higgs coupling in the framework of a simplified 3+1 Dirac neutrino model, that is three light neutrinos plus one heavy neutrino embedded in the Standard Model (SM). The triple Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. The impact of the heavy neutrino can be as large as $+20%$ to $+30%$ for parameter points allowed by the current experimental constraints depending on the tightness of the perturbative bound. This can be probed at the high-luminosity LHC, at future electron-positron colliders and at the Future Circular Collider in hadron-hadron mode, an envisioned 100 TeV $pp$ machine. Our calculation, being done in the mass basis, can be extended to any model using the neutrino portal. In addition, the effects that we have calculated are expected to be enhanced if additional heavy fermions with large Yukawa couplings are included, as in low-scale seesaw mechanisms.
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