The FPL expansion of geometric pushforwards

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Let N=2nN=2n, let FPLr\mathrm{FPL}_r be the set of fully packed loop configurations with connectivity rr, and let μ∗[σr]\mu_*[\sigma_r] be the TT-equivariant KK-theory pushforward to Mat⁡<(N)\operatorname{Mat}_<(N). For each f∈FPLrf\in\mathrm{FPL}_r and each a=1,…,n(n−1)a=1,\ldots,n(n-1), let if,ai_{f,a}, jf,aj_{f,a} and rf,a∈{1,2}r_{f,a}\in\{1,2\} be the indices and plaquette type associated with the configuration, and let m~r\tilde m_r be the normalization monomial.

Geometric FPL expansion conjecture. The pushforward can be decomposed as

μ∗[σr]=∑f∈FPLrmf∏a=1n(n−1)(1−trf,azif,a/zjf,a),\mu_*[\sigma_r]=\sum_{f\in\mathrm{FPL}_r}m_f\prod_{a=1}^{n(n-1)}\left(1-t^{r_{f,a}}z_{i_{f,a}}/z_{j_{f,a}}\right),

where

mf=m~rt−∣{a:rf,a=2}∣/2∏a=1n(n−1)zjf,a.m_f=\tilde m_r t^{-\lvert\{a:r_{f,a}=2\}\rvert/2}\prod_{a=1}^{n(n-1)}z_{j_{f,a}}.

This is the geometric counterpart of the FPL decomposition of Ψr\Psi_r, expressing the pushforward as a sum over configurations. Its resolution is not given in the supplied text.

References

Primary source

A. Knutson and P. Zinn-Justin, “Grassmann-Grassmann conormal varieties, integrability, and plane partitions”, arXiv:1612.04465 (2016).

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