Description
A non-minimally coupled scalar field with quartic self-coupling is widely studied in the literature but the estimation of the unitarity violation scale has not been consistently discussed, especially in the Jordan frame. In this talk, I will show how to consistently calculate the cutoff scale in both the Jordan frame and the Einstein frame, emphasizing the importance of potential of the scalar field. In particular, I will discuss the six-point scattering amplitudes and explicitly show the consistency of the results in both frames as expected.