Bilinear relations for Fourier-transformed Nekrasov functions

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Identify the root lattice of AN−1A_{N-1} with

QN−1=(n1,…,nN)∈ZN∣∑ini=0.Q_{N-1}={(n_1,\ldots,n_N)\in\mathbb{Z}^{N}\mid\sum_i n_i=0}.

For j∈Z/NZj\in\mathbb{Z}/N\mathbb{Z}, define the Fourier-transformed Nekrasov functions by

TjN,k(u⃗,s⃗;q∣z)=∑Λ⃗∈QN−1+ωjsΛZN,k(u⃗qΛ⃗;q−1,q∣z),\mathcal{T}^{N,k}_j(\vec{u},\vec{s};q\mid z)=\sum_{\vec{\Lambda}\in Q_{N-1}+\omega_j}s^\Lambda Z^{N,k}(\vec{u}q^{\vec{\Lambda}};q^{-1},q\mid z),

where ω0=0\omega_0=0 and ωj\omega_j are the fundamental weights of AN−1A_{N-1}. Bilinear relations for Fourier-transformed Nekrasov functions. The functions TjN,k\mathcal{T}^{N,k}_j satisfy

TjN,k(qz)TjN,k(q−1z)=TjN,k(z)2−z1/NTj+1N,k(qk/Nz)Tj−1N,k(q−k/Nz).\mathcal{T}^{N,k}_j(qz)\mathcal{T}^{N,k}_j(q^{-1}z)=\mathcal{T}^{N,k}_j(z)^2-z^{1/N}\mathcal{T}^{N,k}_{j+1}(q^{k/N}z)\mathcal{T}^{N,k}_{j-1}(q^{-k/N}z).

These relations are analogous to the blow-up equations for Nekrasov functions and connect the Fourier-transformed functions with bilinear Toda-type structures. They were conjectured previously and have been proven, so the statement is solved.

References

Primary source

M. Bershtein, P. Gavrylenko and A. Marshakov, “Cluster Toda chains and Nekrasov functions”, arXiv:1804.10145 (2018).

Additional references

2 papers in this index state this conjecture (2016–2018). The statement above is taken from the most recent of them; the others are arXiv:1608.02566.

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