The iterated quantum Frobenius Ext decomposition conjecture

Let FF and GG be strict polynomial functors, let F(s)qF^{(s)_q} and G(s)qG^{(s)_q} denote their ss-th quantum Frobenius twists, and define

Es=ExtPq(I(s)q,I(s)q).E_s=\operatorname{Ext}_{\mathcal{P}^{}_q}^*(I^{(s)_q},I^{(s)_q}).

For each degree kk, the iterated quantum Frobenius Ext decomposition conjecture. There is a graded isomorphism

ExtPqk(F(s)q,G(s)q)i+j=kExti(F,Gj(EsI)).\operatorname{Ext}^k_{\mathcal{P}^{}_q}(F^{(s)_q},G^{(s)_q})\simeq\bigoplus_{i+j=k}\operatorname{Ext}^i(F,G^j(E_s\otimes I)).

The paper states this as a consequence, in characteristic p>0p>0, of the one-step conjecture. It would provide a uniform description of Ext-groups after arbitrary quantum Frobenius twists, beyond the cases computed in the paper.

Sources & referencesView supporting material

Primary source

Deturck Théo, “Ext-group in the category of quantum polynomial functors via the quantum Frobenius twist”, arXiv:2506.05827 (2025).

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