Bilinear relations for Fourier-transformed Nekrasov functions

Identify the root lattice of AN1A_{N-1} with

QN1=(n1,,nN)ZNini=0.Q_{N-1}={(n_1,\ldots,n_N)\in\mathbb{Z}^{N}\mid\sum_i n_i=0}.

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

TjN,k(u,s;qz)=ΛQN1+ωjsΛZN,k(uqΛ;q1,qz),\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 AN1A_{N-1}. Bilinear relations for Fourier-transformed Nekrasov functions. The functions TjN,k\mathcal{T}^{N,k}_j satisfy

TjN,k(qz)TjN,k(q1z)=TjN,k(z)2z1/NTj+1N,k(qk/Nz)Tj1N,k(qk/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.

Sources & referencesView supporting material

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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