We find that multiple vertex algebras can arise from a single 4d N=2 𝒩 = 2 superconformal field theory (SCFT). The connection is given by the BPS monodromy operator M M, which is a wall-crossing invariant quantity that captures the BPS spectrum on the Coulomb branch. For a class of low-rank Argyres-Douglas theories, we find that the trace of the multiple powers of the monodromy operator Tr MN M N yield modular functions that can be identified with the vacuum characters of certain vertex algebra for each N N. In particular, we realize unitary VOAs of the Deligne-Cvitanović exceptional series type (A₂) ₁ (A 2) 1, (G₂) ₁ (G 2) 1, (D₄) ₁ (D 4) 1, (F₄) ₁ (F 4) 1, (E₆) ₁ (E 6) 1 from Argyres-Douglas theories. We also find the modular invariant characters of the ‘intermediate vertex algebras’ (E₇₁₂) ₁ (E 7 1 2) 1 and (X₁) ₁ (X 1) 1. Our analysis allows us to construct 3d N=2 <
Kim et al. (Tue,) studied this question.