  We perform a comprehensive numerical study of gravitational waves from
stellar core collapse in the massive scalar-tensor theory with the cubic and
quartic self-interactions of the scalar field. We investigate the dependence of
gravitational waves on the self-interaction as well as the mass of the scalar
field and the conformal factor. We find that gravitational-wave spectra show a
systematic difference between the cubic and quartic self-interactions. We also
find that this systematic difference is insensitive to the mass of the scalar
field and the conformal factor. Our results indicate that the type of the
self-interaction could be constrained by observations of gravitational waves
using the future-planned detectors.
