Explicit basis conjecture for parabolic invariants of truncated polynomial rings

From papers

Let Qm(n)=Fq[x1,,xn]/(x1qm,,xnqm){\mathcal{Q}}_m(n)=\mathbb{F}_q[x_1,\ldots,x_n]/(x_1^{q^m},\ldots,x_n^{q^m}), let P(α)P(\alpha) be the parabolic subgroup associated to a composition α=(α1,,α)\alpha=(\alpha_1,\ldots,\alpha_\ell), and let δa;b\delta_{a;b}, Φ\Phi, and Δsm\Delta_s^m be the operators and Dickson-algebra subspaces defined in the source. For a weak composition βα\beta\leq\alpha with βm|\beta|\leq m, set Bi=β1++βiB_i=\beta_1+\cdots+\beta_i and B0=0B_0=0, and choose

fiΦBi1ΔβimBi1ΔBimBi.f_i\in\Phi^{B_{i-1}}\Delta_{\beta_i}^{m-B_{i-1}}\subseteq\Delta_{B_i}^{m-B_i}.

Explicit parabolic basis conjecture. The resulting elements

δB1+1;mα1β1(f1δB2+1;mα2β2(f1δB+1;mαβ(f)))\delta_{B_1+1;m}^{\alpha_1-\beta_1}\bigg(f_1\delta_{B_2+1;m}^{\alpha_2-\beta_2}\big(\cdots f_{\ell-1}\delta_{B_\ell+1;m}^{\alpha_\ell-\beta_\ell}(f_\ell)\big)\bigg)

form the set Bm(α)\mathcal{B}_m(\alpha), and Bm(α)\mathcal{B}_m(\alpha) is an Fq\mathbb{F}_q-basis of Qm(n)P(α){\mathcal{Q}}_m(n)^{P(\alpha)}. This refines the parabolic Hilbert-series conjecture by proposing explicit basis elements, but the source supplies no resolution status.

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Sources & referencesView supporting material

Primary source

Le Minh Ha, Nguyen Dang Ho Hai and Nguyen Van Nghia, “On Modular Invariants of Truncated Polynomial Rings in low ranks”, arXiv:2408.16250 (2025).

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