Enhanced di-Higgs production from TeV-scale heavy neutral leptons at future lepton colliders

Within the context of heavy neutral lepton extensions of the Standard Model, we consider the rare di-Higgs production mode $\ell^+\ell^-\to hh$ at future high-energy lepton colliders. As a concrete example, we study the impact of a low-scale Inverse Seesaw realisation on the prospects for di-Higgs production. Our results show that the presence of TeV-scale heavy neutral leptons can enhance the cross-section by up to factor 60. We further comment on the interplay with electroweak precision observables, showing that bounds on the di-Higgs production cross-section at future high-energy lepton colliders could serve as complementary probes of low-scale seesaw scenarios.