  In quasi-single field inflation models, massive isocurvature modes, that are
coupled to the inflaton and have mass of order the Hubble parameter, can have
nontrivial impacts on density perturbations, especially non-Gaussianities. We
study a simple example of quasi-single field inflation in terms of turning
inflaton trajectory. Large bispectra with a one-parameter family of novel
shapes arise, lying between the well-known local and equilateral shape. The
trispectra can also be very large and its magnitude tNL can be much larger than
fNL squared.
