Generalized Dynkin-diagram modularity conjecture for Nahm quadruples

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Let XX and YY be Dynkin diagrams of type ABCDEFGTABCDEFGT, with Cartan matrices C(X)C(X) and C(Y)C(Y). Let D(X)D(X) be the diagonal matrix whose jj-th diagonal entry is αj2/β2\alpha_j^2/\beta^2, where αj\alpha_j is the jj-th simple root and β\beta is a short root. Define

A(X,Y)=C(X)⊗C(Y)−1,D(X,Y)=D(X)⊗D(Y),A(X,Y)=C(X)\otimes C(Y)^{-1}, \qquad D(X,Y)=D(X)\otimes D(Y),

where ⊗\otimes is the Kronecker product. Set C(X,Y)=−c(X,Y)/24C(X,Y)=-c(X,Y)/24, with

c(X,Y)=tr⁡(D(X,Y))h(X)h(X)+h(Y),c(X,Y)=\frac{\operatorname{tr}(D(X,Y))h(X)}{h(X)+h(Y)},

where h(−)h(-) is the Coxeter number. Generalized modularity conjecture. The quadruple (A(X,Y),0,C(X,Y),D(X,Y))(A(X,Y),0,C(X,Y),D(X,Y)) is a modular quadruple. The statement has been disproved: Wang found counterexamples to Zagier's duality conjecture and its generalization, so the supplied status evidence marks this conjecture as refuted.

References

Primary source

Kaiwen Sun and Haowu Wang, “Dynkin diagrams, generalized Nahm sums and 2d CFTs”, arXiv:2604.00847 (2026).

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