Singularities of Schubert varieties, tangent cones and Bruhat graphs
Bibliographic record
Abstract
Let G be a semi-simple algebraic group without G 2 -factors over an algebraically closed field k of characteristic p ≠ 2, 3, and suppose B is a Borel subgroup, T ⊂ B is a maximal torus, and P is a parabolic in G containing B . In an earlier paper, the authors classified the singular T -fixed points x of an arbitrary irreducible T -stable subvariety X in G/P in all characteristics, the key to this being the notion of a Peterson translate. In particular, we showed that if X is Cohen-Macaulay, then X is smooth at x if and only if there exists a T -invariant curve in X through x which contains a smooth point of X and dim Θ x(X) = dim X , where Θ x(X) is the linear span of the reduced tangent cone to X at x . The purpose of this paper is to describe Θ x(X) when X is a Schubert variety in G/P and x is a maximal singular T -fixed point of X . In fact, we give two characterizations. We first show that in all characteristics, Θ x(X) is the sum of all the Peterson translates at x . The second characterization involves further study of the Peterson translates, along the good T -invariant curves at x , for which the assumption char( k ) ≠ 2, 3 is needed. This leads to the following consequence: if x is a maximal singularity of X which is rationally smooth, then either the span of the tangent lines to the T -stable curves is not a module for the isotropy subgroup of B at x , or there exist a pair of orthogonal T -invariant curves at x which determine what we call a B 2 -pair. This characterization gives a nonrecursive algorithm for finding the singular locus of an arbitrary Schubert variety in G/P in terms of its Bruhat graph.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".