  Within models containing a very light scalar particle coupled to the 125 GeV
Higgs boson, we present the first detailed study of Higgs decays into three of
these light scalars. We determine model-independent conditions which the scalar
sector after electroweak symmetry breaking has to satisfy in order for the
three-body channel to become relevant. Using a specific model -- the real
scalar singlet-extension of the Standard Model (SM) -- we then identify
scenarios, where the rates of scalar three-body Higgs decays are comparable to
or even exceed those of the well-studied two-body channel. All those scenarios
are shown to be compatible with current experimental and theoretical
constraints. We finally argue that scalar three-body Higgs decays lead to
exciting new collider signatures with six SM fermions in the final state.
Calculating the corresponding event rates, we find that e.g. six-muon or
six-tau final states may be in reach of dedicated searches at the LHC or ILC
experiments.
