New Physics from Higgs Self-coupling Measurement *

Measurement of the triple Higgs boson coupling is one of the most important goals of the Higgs physics at a future ee linear collider (LC) experiment. This would provide the first direct information on the Higgs potential that is responsible for electroweak symmetry breaking. The existence of the triple Higgs coupling is a characteristic feature of the spontaneous breaking of the electroweak symmetry in models with only weak-doublet Higgs fields, since there is no term with an odd number of scalar fields in the original Lagrangian. Experimentally, the triple Higgs (hhh) coupling is determined from the double Higgs production processes, ee → Zhh and ee → νν̄hh (W fusion process). The precision of the coupling determination is estimated as about 20% (10%) at 500 GeV (1 TeV) LC with an integrated luminosity of 1 ab. 1 In this talk, we discuss new physics effects on the hhh coupling constant. In particular, we take a Two Higgs Doublet Model (THDM) as an example of physics beyond the Standard Model (SM), and consider relationship between the radiative correction to the hhh coupling constant and the condition for successful electroweak baryogenesis. Details on the calculation are presented elsewhere.