Exotic Higgs Decay h to 2a at the International Linear Collider: a Snowmass White Paper

A Higgs factory like the International Linear Collider (ILC) can play a significant role in searching for exotic decays of Higgs bosons. As an illustration, we investigate the ILC sensitivity for the decay topology $h\to a_1 a_1 \to \tau\bar \tau\tau \bar \tau$ in the Next-to-Minimal-Supersymmetric-Standard-Model (NMSSM). Here $h$ can be either Standard-Model-like or non-standard, and $a_1$ is the lightest CP-odd Higgs boson. We also compare results to expectations for this channel at the LHC.