  We perform multi-dimensional core-collapse supernova (CCSN) simulations in a
massive scalar-tensor theory for the first time with a realistic equation of
state and multi-energy neutrino radiation. Among the set of our models varying
the scalar mass and the coupling strength between the scalar and gravitational
fields, a particular model allows for recurrent spontaneous scalarizations
(SSs) in the proto-neutron star (PNS). Each SS induces the PNS collapse and
subsequent bounce, from which devastating shock waves emanate and eject the PNS
envelope. The explosion energy can easily exceed $\mathcal O(10^{51})$ erg.
This study reveals new aspects of SS as the explosion mechanism of CCSNe. We
also discuss its characteristic multi-messenger signals: neutrinos and
gravitational waves.
