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The degenerate and nondegenerate Ariki theorems have distinct parameter ranges
Statement
Assume inherited AC The Axiom of Choice for the category-O, Schur and highest-weight/global-basis suppliers. The explicit finite spectral and algebra-transport constructions introduce no additional choice.
The degenerate theorem The degenerate Ariki categorification theorem concerns the tower over with integral multicharge , additive cyclotomic roots and the Fock/highest-weight data. Its integral Grothendieck-group, projective/simple, standard-class and decomposition-number identifications are ungraded at the basis parameter one. This parameter is independent of the numerical nondegenerate Hecke parameter .
In the generic branch, let have infinite multiplicative order and let be any finite ordered integral multicharge, including repeated charges. Put . Residues are integers and the datum is the directed line , of type and quantum characteristic . The actual word-preserving tower isomorphism constructed through the common integer-line KLR algebra identifies the degenerate and generic nondegenerate categorifications, including their full integral based families and their standard classes. At a primitive -th root of unity , the residue datum is instead cyclic affine type , with a double edge at ; that theorem requires its own comparison and categorification. It does not follow by specializing the generic tower isomorphism.
Generic comparison and standard classes
Write for the first-strand quotient and for in Affine type-A presentations and charged cyclotomic quotients. The proved support and two local inverse dictionaries give a coherent tower isomorphism with for every integer word , where the eigenvalues are and , respectively. Pullback is an exact equivalence preserving all residue induction/restriction bimodules and their compositions.
For an ordered multipartition of , let be the intrinsic Murphy cell Specht of Arbitrary-level cyclotomic Hecke, Murphy cell and multipartition Schur modules, converted from right to left through the generator-fixing star anti-involution. Let be the actual affine-induced Specht of Schur functor images of standard, simple, projective and tilting objects, with factors in that component order. Then This is equality of classes, not an asserted isomorphism of the Specht modules. It does not identify an untwisted ordinary same-shape simple with a transported crystal simple.
To use the source Fock labels for an arbitrary charge order, choose the fixed stable permutation sorting the pairs into decreasing charges and write the sorted pairs again with indices . On a sufficiently low common finite cut, define the column-strict label by Its remaining tail is ground. Adding the box has integer residue . The sorted intrinsic standard is the Schur image of , so under the generic identification its class maps to . Sorting paired components preserves the word-character sum and hence this class; it does not assert an equivalence of the different parabolic category-O realizations.
Preserved based families and all cuts
Define and , where is the projective cover of . The generic identifications give Thus is the full standard highest-weight lattice and the full restricted integral costandard lattice. The projective canonical and simple dual-canonical families, the Cartan Hom pairing, its dual cover/simple bases, the Cartan map as the lower-to-upper lattice inclusion, the Chevalley operators and their integral divided-power actions all transfer. The costandard lattice is not asserted to be integrally generated by its ground vector. In the transported simple basis the generic standard multiplicities are exactly
For every admitted consecutive , including and half-infinite intervals, these assertions hold on the same supported central content cuts. Finite letter cuts contain all charges; finite root cuts contain the selected content and every intermediate content of the chosen residue operations. Compatible lower and upper cuts append the common ground tail and leave added top letters absent. They identify the same finite algebras, word projectors, based labels, bimodules and standard classes on overlaps, so the full restricted direct sums glue. A proper supported cut is retained as a cut and is not identified with the whole rank algebra. Rank zero is the ground line; at level zero both positive-rank towers vanish and only that rank-zero line survives.
Root parameters and characteristics
For the level-one root-of-unity track the regime is charge , , and finite quantum characteristic . In characteristic zero, global-basis coefficients give the characteristic-zero decomposition theorem with the track's fixed partition and sign conventions. Its graded version also requires the transported KLR grading and graded categorification; an ungraded coefficient at basis parameter one is not a graded decomposition polynomial. In characteristic a primitive -th root in a field requires ; the characteristic-zero generic equivalence makes no assertion that the positive-characteristic adjustment matrix is the identity.
The degenerate parameter has quantum characteristic over , but quantum characteristic over characteristic . Thus the degenerate branch is not uniformly across fields. Cross-characteristic root-of-unity comparisons require their own suppliers; no general positive-characteristic decomposition formula is claimed.
Facts & Assumptions
Given: The inherited AC, a finite integral multicharge, the two cyclotomic towers over , a parameter of infinite order, their intrinsic standards, and the actual local and categorical suppliers below.
Generic support is finite in each rank, with colors within of a charge, and the two integer-color local inverse tables glue to actual word-preserving tower maps and residue bimodules (Generic cyclotomic type-A support is bounded by rank ↗, Integer-color degenerate Hecke–KLR local inverse tables ↗, Generic nondegenerate local inverse tables on integer colors ↗, Generic cyclotomic local dictionaries glue to a tower ↗).
The arbitrary-level Murphy basis is finite free and its commuting act on the cell basis with dominance-triangular diagonal at node (Arbitrary-level cyclotomic Hecke, Murphy cell and multipartition Schur modules, Arbitrary-level Murphy Jucys–Murphy action is content triangular). This is a universal parameter identity, not an invocation of a finite- label theorem at .
The actual Schur standard is affine induction of evaluated ordinary complex Spechts; its affine action factors through the cyclotomic quotient (Schur functor images of standard, simple, projective and tilting objects). The affine PBW basis and evaluation are proved in The degenerate affine Hecke algebra, and the ordinary Specht joint eigenbasis has one vector for each standard tableau, with eigenvalues (The joint spectrum of the Jucys-Murphy elements is the set of tableau content vectors).
The actual degenerate and identifications give the full lower and upper integral lattices, normalized cover/simple families, Chevalley and divided-power operators and all compatible finite cuts (The degenerate cyclotomic Hecke projective is the highest weight module, The degenerate cyclotomic Hecke is the dual highest weight module, The degenerate Ariki categorification theorem). The standard images and their multiplicities are Degenerate Specht decomposition numbers are canonical basis coefficients at one, with the column-label convention of The higher-level wedge-tensor Fock module.
The Cartan Hom pairing has integral dual projective-cover/simple bases (Projective and simple classes are dual bases under splitting).
Proof
The actual generic tower comparison. Use the first-strand presentations and the finite support of [F1]. On a first color , the two cyclotomic polynomials become times an invertible nilpotent-evaluated series, since and when . Thus the proved affine inverse dictionaries descend in both directions to the same homogeneous cyclotomic KLR presentation. Their inverse composites fix words, dots and crossings, with the prescribed right-side order of their series. This gives the actual maps and hence ; no arbitrary rankwise isomorphism is selected. Their local series are independent of rank, charge order and window. The prefix projector is the sum over its appended colors, so the tower maps agree; the common last-color idempotent identifies the two induction bimodules by , and identifies the restrictions. In a fixed finite rank bound every series is a finite nilpotent Taylor sum; window enlargement adds only zero unsupported words. Therefore the comparison preserves actual word projectors, residue functors and their finite compositions.
Word characters and the generic Murphy standard. Define and , with finite sums in rank by [F1]. An idempotent image is an exact functor, so both characters are additive and descend to . Infinite order makes injective. Order the Murphy basis by a linear extension of dominance; [F2] gives a simultaneous flag for the commuting , with one-dimensional factors of eigenword . Applying the exact primary word projector to this flag counts each matching factor once and every nonmatching factor zero, even when distinct tableaux give the same word. Star fixes every , so right-to-left conversion preserves these dimensions. Hence .
The actual degenerate standard character. Put and . The affine PBW basis of [F3], read also in reverse order through its generator-fixing anti-involution, makes the affine algebra free as a right affine Young-subalgebra module on the distinguished finite shuffles . Thus the actual induced standard has basis , where is a tensor of ordinary Specht eigenvectors. The mixed relation moves a polynomial generator through the shuffle as : each scalar correction deletes a crossing. Reducing to its minimal Young-coset representative cannot increase length. Therefore the shuffle-length filtration is stable under all commuting , and its factors have the permuted component eigenwords of [F3]. Each component standard-tableau tuple and order-preserving shuffle specifies one standard multitableau, and conversely a multitableau recovers that tuple and shuffle by local renumbering. Applying exact word projectors to this filtration consequently gives , with full multiplicities. The joined Schur theorem [F3] identifies this actual affine-induced module with the Schur image; a proposed finite-W or Hecke character is not substituted for that module.
Injectivity from actual projective words. For put , where the ground object is projective. The actual right-appending residue bimodules identify with by repeated balanced tensor multiplication. Evaluation at the idempotent gives , so its Cartan pairing is exactly the corresponding word-character coefficient. Under the projective highest-weight theorem [F4], the classes of these words span each rationalized weight: the lower lattice is ground-generated under divided powers, and over each divided power is an ordinary power divided by a factorial. Therefore an integral class of zero character pairs to zero with every projective cover. The integral dual bases in [F5] make every simple coefficient zero, proving word-character injectivity on , not just on its rationalization. Only the lower projective lattice is used for this spanning argument; integral ground cyclicity of the full upper lattice is not assumed.
Exact standard classes and charge order. Step 1.1 makes pullback preserve every word coefficient. Steps 1.2–2.1 give equal characters for and , and step 2.2 gives their equality in integral . A simultaneous permutation of charges and partitions bijects their standard tableaux without changing a residue word, so it preserves both character sums and, by step 2.2, the degenerate standard class. Sort these pairs into the source charge order. The entries are strictly decreasing down the column and have the ground tail; their ground differences are exactly the component partitions. The source Schur/Fock dictionary [F3, F4] therefore sends the sorted standard class to . This proves the stated generic standard-class dictionary for every finite integral charge order. The calculation uses the same-shape Murphy cell and its star conversion. A convention using a contragredient dual has the same primary dimensions because star fixes the polynomial generators; a signed-conjugate convention must also carry its sign and charge/reflected-residue change. No untwisted conjugate module or unchanged signed residue word is inferred.
Transfer the full based and pairing data. An algebra isomorphism gives an exact equivalence and a Hom bijection on every pair. Thus it takes simples to simples, indecomposable projectives to indecomposable projectives and projective covers to the corresponding covers, defining precisely and . It preserves the Cartan pairing and the inclusion of projective classes into module classes. Composing with [F4] therefore transfers the full lower and restricted upper integral lattices, their normalized canonical/dual-canonical families at , and the Cartan map as their lattice inclusion. The bimodule maps in step 1.1 transfer the Chevalley actions, and the integral divided-power actions transfer under these integral group isomorphisms. Combining step 3.1 with the degenerate standard multiplicities of [F4] gives . This coefficient comparison is in the transported simple basis and implies neither a Specht-module isomorphism nor a same-shape cellular-head identification.
All compatible cuts and all ranks. On a content , the sum of word projectors with that content is preserved by , as is the central sum over words in any supported interval . Hence the same comparison restricts to the same supported finite content algebras and to their residue corners. For any selected finite list of contents and operations, choose lower/upper letter and root cuts containing all charges, content supports and intermediate supports; [F1] permits a common finite generic window, and [F4] identifies the actual degenerate finite-cut based lattices and standards by their common-ground-tail labels. The inverse dictionaries use fixed pair series, so the tower isomorphisms agree on overlaps. The unchanged intrinsic affine standards and their corner projections have the same characters and classes there. Thus their standard, simple and projective classes, pairings and integral lower/upper bases glue under the same composable tail maps, proving the full arbitrary-consecutive- assertion weight by weight. No proper supported cut becomes the whole rank algebra. At rank zero both maps are the identity on , with the empty word, tableau and standard. At level zero the first cyclotomic polynomial is , so both positive-rank algebras and all residue operations are zero, and only the ground line remains.
The root-of-unity obstruction and characteristic boundary. For level one with charge zero and , the degenerate presentation gives , and , hence . At the nondegenerate level-one presentation gives , and , hence . Its class is nonzero and nilpotent, whereas the product of two fields has no nonzero nilpotent. These algebras are therefore not isomorphic. Moreover, the generic local inverse series rely on for distinct integers; these constants can vanish at a root of unity, so the proved generic inverse maps cannot simply be specialized there. The cyclic characteristic-zero and positive-characteristic assertions retain their own parameters and suppliers, and the grading/basis variable is never identified with the numerical . This proves the stated obstruction and all comparison claims without claiming a general positive-characteristic decomposition formula. The only choice is the inherited AC in [F4]; the remaining constructions use finite data.
Depends on
- The degenerate Ariki categorification theorem
- The degenerate cyclotomic Hecke $G_0$ is the dual highest weight module
- The degenerate cyclotomic Hecke projective $K_0$ is the highest weight module
- Degenerate Specht decomposition numbers are canonical basis coefficients at one
- Schur functor images of standard, simple, projective and tilting objects
- The degenerate cyclotomic Hecke algebra
- The degenerate affine Hecke algebra
- The degenerate cyclotomic Hecke tower and its residue functors
- Affine type-A presentations and charged cyclotomic quotients
- Arbitrary-level cyclotomic Hecke, Murphy cell and multipartition Schur modules
- Arbitrary-level Murphy Jucys–Murphy action is content triangular
- The joint spectrum of the Jucys-Murphy elements is the set of tableau content vectors
- Projective and simple classes are dual bases under splitting
- The higher-level wedge-tensor Fock module
- The generic type-A Hecke algebra
- The Axiom of Choice
Used by
Dependency tree · two levels
120 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Jonathan Brundan and Alexander Kleshchev, Blocks of cyclotomic Hecke algebras and Khovanov-Lauda algebras, arXiv:0808.2032v4 (standard reference, not scraped)
- Jonathan Brundan and Alexander Kleshchev, The degenerate analogue of Ariki's categorification theorem, arXiv:0901.0057v1 (standard reference, not scraped)