Generalized Dynkin-diagram modularity conjecture for Nahm quadruples

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.

Sources & referencesView supporting material

Primary source

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

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