One-loop effective action up to dimension eight: integrating out heavy scalar(s)

We present the one-loop effective action up to dimension eight after integrating out degenerate scalars using the Heat-Kernel method. The result is provided without assuming any specific form of either UV or low energy theories, i.e., universal. In this paper, we consider the complete effects of only heavy scalar propagators in the loops. We also verify part of the results using the covariant diagram technique.