The even and odd Nahm sum identities for Z^e(q)\hat{Z}_e(q) and Z^o(q)\hat{Z}_o(q)

Let qq be a formal variable, let (q2;q2)n=r=1n(1q2r)(q^2;q^2)_n=\prod_{r=1}^{n}(1-q^{2r}) for n0n\geq 0, let Jm=(qm;qm)J_m=(q^m;q^m)_\infty, and define the bilateral theta-type series f(x,y)=rZxr(r+1)/2yr(r1)/2f(x,y)=\sum_{r\in\mathbb Z}x^{r(r+1)/2}y^{r(r-1)/2}. Define

Z^e(q)=a,j,s0qa2aj+j2j+2s2+2s2sj(q2;q2)a(q2;q2)j(q2;q2)2s,\hat{Z}_e(q)=\sum_{a,j,s\geq 0}\frac{q^{a^2-aj+j^2-j+2s^2+2s-2sj}}{(q^2;q^2)_a(q^2;q^2)_j(q^2;q^2)_{2s}},

and

Z^o(q)=a,j,s0qa2aj+j2j+2s2+4s+1(2s+1)j(q2;q2)a(q2;q2)j(q2;q2)2s+1.\hat{Z}_o(q)=\sum_{a,j,s\geq 0}\frac{q^{a^2-aj+j^2-j+2s^2+4s+1-(2s+1)j}}{(q^2;q^2)_a(q^2;q^2)_j(q^2;q^2)_{2s+1}}.

The even and odd Nahm sum conjecture.

Z^e(q)=3J33J1J22J6f(q4,q8),\hat{Z}_e(q)=3\frac{J_3^3}{J_1J_2^2J_6}f(q^4,q^8),

and

Z^o(q)=3J33J1J22J6f(q2,q10).\hat{Z}_o(q)=3\frac{J_3^3}{J_1J_2^2J_6}f(q^2,q^{10}).

If established, this conjecture implies the Cao–Wang identity above. It is presented as a conjecture in the paper and is connected there to a conjecture of Shi and Wang; no resolution is supplied in the given text.

Sources & referencesView supporting material

Primary source

Haijun Li, “Proofs of five conjectural identities on modular rank four Nahm sums”, arXiv:2606.25866 (2026).

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