  In this short note we translate the best available observational bounds on
the CMB bispectrum amplitudes into constraints on a specific scale-invariant
New Physics Hypersurface (NPH) model of vacuum state modifications, as first
proposed by Danielsson, in general models of single-field inflation. As
compared to the power spectrum the bispectrum constraints are less ambiguous
and provide an interesting upper bound on the cut-off scale in general models
of single-field inflation with a small speed of sound. This upper bound is
incompatible with the power spectrum constraint for most of the parameter
domain, leaving very little room for minimal cut-off vacuum state modifications
in general single-field models with a small speed of sound.
