  We investigate resonant di-Higgs production as a means of probing extended
scalar sectors that include a 125 GeV Standard Model-like Higgs boson. For
concreteness, we consider a gauge singlet Higgs portal scenario leading to two
mixed doublet-singlet states, h_1,2. For m_h_2 > 2 m_h_1, the resonant di-Higgs
production process p p -> h_2 -> h_1 h_1 will lead to final states associated
with the decaying pair of Standard Model-like Higgs scalars. We focus on h_2
production via gluon fusion and on the b b tau^+ tau^- final state. We find
that discovery of the h_2 at the LHC may be achieved with ~ 100 fb^-1 of
integrated luminosity for benchmark parameter choices relevant to cosmology.
Our analysis directly maps onto the decoupling limits of the Next-to-Minimal
Supersymmetric Standard Model (NMSSM) and more generically onto extensions of
the Standard Model Higgs sector in which a heavy scalar produced through gluon
fusion decays to a pair of Standard Model-like Higgs bosons.
