The method of regions, a systematic approach to the asymptotic expansions of Feynman integrals, suggests that a Feynman integral can be reconstructed by summing over integrals expanded in certain regions. This technique not only facilitates the computation of Feynman integrals but also provides valuable insights for formulating an EFT, such as the Soft-Collinear Effective Theory (SCET). However, a fundamental question remains unanswered for most cases: how does one systematically determine the entire list of regions?
This talk aims to address this question by drawing from some recent research works. In general, we classify the regions into two types, "facet regions" and "hidden regions". After a brief introduction, we will demonstrate the following results in detail. 1. For the "on-shell expansion" and the "soft expansion" of massless wide-angle scattering, an all-order result for facet regions is validated: only the hard mode, collinear modes, and ultrasoft mode are involved, with their interactions following certain rules. We have also found ample evidences that the same holds for hidden regions. 2. For the two-to-two forward scattering in the Regge limit, more complicated mode structures occur from three loops. In particular, hidden regions all feature the Glauber mode. Some important implications from these results will also be discussed in the talk.