Coleppa, BaradhwajBaradhwajColeppaKhanna, AkshatAkshatKhannaKrishna, Gokul B.Gokul B.Krishna2026-03-182026-03-182026-03-011434-604410.1140/epjc/s10052-026-15413-9https://repository.iitgn.ac.in/handle/IITG2025/34866The Three-Higgs-Doublet Model (3HDM) extends the Standard Model by introducing two additional scalar doublets, leading to a rich spectrum of new particles: three neutral CP-even Higgs bosons (h1, H2, H3), two neutral CPodd Higgs bosons (A2, A3), and two charged Higgs bosons (H+ 2 , H+ 3 ). In this work, we present a phenomenological study of the 3HDM at the future International Linear Collider (ILC) with a center-of-mass energy of √s = 1000 GeV. Applying a comprehensive set of theoretical and experimental constraints, we identify promising new physics signals with sufficiently large production cross-sections. Our analysis shows that e+e− → H2 A2, e+e− → H2H2Z, A2 A2Z, H2H± 2 W∓, A2H± 2 W∓ and H1H2 A2 are among the most sensitive channels to probe this extended Higgs sector. We demonstrate that a future ILC would offer a powerful platform to test these interactions and discover these heavier Higgs bosons thus providing evidence of physics beyond the Standard Model.en-USArticle1434-6052