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The dual-canonical, canonical and quasi-canonical Fock bases
Definition
Assume inherited AC The Axiom of Choice for the invoked quantum based/global lattice and normalized quasi- suppliers.
Work in the conventions of The higher-level wedge-tensor Fock module and The Fock-space convention dictionary for finite type-A quantum modules: the source parameter is , the library parameter is , the monomial basis of the Fock module is , and is the ordinary compatible bar of The tensor-product bar on the Fock module and its truncation compatibility, which is triangular and integral on the monomial basis.
The source dual-canonical family is the unique -fixed family with and the canonical family is the unique -fixed family with
Let and be the transition coefficients defined by and define the quasi-canonical family by The families and are ordinary-bar fixed; generally is not.
The reverse-factor monomials use the reverse-column reading of the tableau ; the corresponding bar-fixed families are defined by the same triangular conditions with respect to , so that is supported on . Rectification is the weight-preserving combinatorial identification of the original lower ground component with the reverse-factor lower ground component , given by reading down columns and reverse row insertion.
The source sesquilinear form is the -antilinear-in-the-first argument pairing with and the bilinear reverse-factor form is Thus the labelled monomial Gram matrices of the two forms are the inverse ordinary-bar matrix, not the identity. Transition duality gives
All four families are Laurent-integral bases of the finite Fock cuts and commute with the upper-cut and common-bottom-tail embeddings. On a highest constituent, the source bilinear normalization and the library polarization of The upper (form-dual) global basis and the required perfectness of the integral pairing differ by an explicit weight power, proved in the global-basis comparison later in this pair; no unqualified library-upper/ordinary-bar identification is asserted.
Facts & Assumptions
Given: Assume inherited AC The Axiom of Choice for the invoked quantum suppliers. A finite cut of the Fock module with its monomial basis , the ordinary compatible bar with , the reverse-column reading and rectification, and the two forms of the Definition.
Fock bar and monomial basis (The tensor-product bar on the Fock module and its truncation compatibility, The column monomial basis of the higher-level Fock module, The higher-level wedge-tensor Fock module): is involutive, triangular with coefficients in , preserves the integral monomial lattice, and commutes with the cut embeddings; the monomials form a Laurent-integral basis.
Normalized finite quasi- intertwiner (Existence and uniqueness of the weightwise quasi- intertwiner, The quasi- intertwiner determines its inverse and the coproduct factorizations): the positive-first/negative-second family is uniquely determined by and , with , and its finite-cut evaluations are the tensor bars of [F1].
Verification
The two triangular charts. Fix a total order refining the finite-cut Bruhat order. Construct a fixed vector with leading term by descending elimination on its lower support. Suppose its bar discrepancy has largest remaining term ; involutivity gives , since every higher discrepancy has already vanished. Write . There is a unique in with , and a unique in with the same property. Adding the relevant removes this discrepancy and changes only smaller ones. Finite descending elimination constructs the two charts, with uniqueness by the same largest-coefficient argument. This explicitly retains conjugation in the fixed-vector equation . Each chart is integral unitriangular, hence an integral basis.
Rectification of the ground components. On a column cancel the simultaneous occurrences; concatenate the column words and cancel pairs. In reverse tensor order this is the lower rule with ordinary column reading. Weakly increasing rows are stable: a changed entry violating the neighboring row inequality would have an equal neighboring entry giving a later surviving or earlier surviving , contrary to the selected extremum; if that neighboring sign is cancelled, column strictness gives its matching mate in the same intervening strip and cancels the selected sign too. Apply this matching successively across neighboring columns, including unequal heights. The only highest tableau in this closed set is ground: starting at the rightmost column, absence of unmatched minus forces consecutive bottom entries from the alphabet minimum; induct leftward using row inequalities on the overlap, while a gap above it gives an unmatched minus with no right-hand mate. Raising decreases the entry sum to its finite lower bound, so the whole closed standard set is the reverse lower ground component. For the original lower order read columns from the right and align their tops; the same argument gives the reverse-standard set. Insert its reverse-column word by bumping the smallest larger entry. Adjacent insertions differ by the Knuth moves for and for . Cancelling the three-letter signatures for each adjacent alphabet pair preserves their unmatched counts and selected sign, and the changed entry follows its bump path, so insertion commutes with crystal edges. Reverse insertion, bumping the largest smaller entry in the backward column word, reverses each successive bump path and preserves the row and column inequalities. Thus the two procedures are inverse, weight preserving, send ground to ground and identify with in the asserted lower charts.
The Gram matrices. Put with , and write . The normalization says , since the second argument is linear. Therefore , with no transpose. Exactly the same equation holds for , since its second argument is also linear, so its matrix is again . Involutivity says , hence .
The quasi-canonical family and the inverse charts. Let be the coefficient matrix of in , with columns labelled by vectors, and set . The coefficient of in is , while . The coefficient matrix of is , whose inverse is . These identities prove both displayed quasi-canonical expansions with the stated index positions and show integrality. The fixed-chart equation is , where coefficient conjugation sends to .
Cuts and integrality. All four families are computed weight by weight from the same triangular equations, so they are Laurent-integral bases of each finite cut. Since the embeddings of [F1] preserve the monomial basis and the bar, they preserve these equations and hence the four families; on the highest constituent the normalized source pairing is up to the explicit weight rescaling proved in the global-basis comparison.
The reverse-bar adjoint calculation. Let be the linear anti-automorphism , , ; reversing products preserves the toral mixed, commutator and Serre relations. Write . The source coproduct has , . Put . Direct substitution gives and ; the toral coproduct is unchanged. Hence and on the generated algebra. Applying the anti-automorphism to gives . Its degree-zero term is one and flip with exchange preserves the positive-first/negative-second completion. The exact normalized uniqueness of [F3] therefore gives . On each ordered minuscule wedge factor the matrices are mutually transpose and the matrices are diagonal, so transpose realizes . Consequently transposing the original two-factor bar and reversing factors gives the reverse-factor bar in the same tableau labelling. The same statement for successive prefixes follows from the coproduct factorization and parenthesization independence of [F1], [F3]; thus . In raw full-tensor labels this also reads , , where the bar acts on matrix coefficients and conjugates all toral weight powers. Finally , so . This adjoint calculation uses the two ordinary tensor bars independently of charge transpose.
The sesquilinear delta identity. By step 2.1 the coefficient matrices are for and for , with . Thus the pairing matrix is . The fixed-chart equation gives , so this product is . This proves directly, including coefficient conjugation.
The reverse-factor delta identities. Let and be the coefficient matrices of and . Since , their pairing matrix is . Both and have coefficients in , so this matrix lies in . Step 2.3 makes each entry bar fixed, because the vectors being paired are fixed. The only bar-fixed polynomial in is zero, proving . Replacing the positive charts by and gives a matrix in and the same bar argument, proving .
Conclusion. The four families and their reverse-factor counterparts are well-defined Laurent-integral bases of the finite Fock cuts with the stated triangular charts and delta pairings, and the reverse ground component is identified with by rectification. All later comparisons with the library upper family use the explicit weight rescaling of the global-basis theorem, never the bare names of the families.
Remarks
Context only: Global bases in the library (The lower global basis of and of a highest weight module, The upper (form-dual) global basis and the required perfectness of the integral pairing, Bar invariance, congruence and uniqueness of the lower global basis, The bar lattice and the divided-power integral lattice of a based module): existence, bar invariance and uniqueness of the lower global basis, the form-dual upper basis, and the bar lattice/based-module framework.
Depends on
- The Axiom of Choice
- Existence and uniqueness of the weightwise quasi-$R$ intertwiner
- The quasi-$R$ intertwiner determines its inverse and the coproduct factorizations
- The tensor-product bar on the Fock module and its truncation compatibility
- The column monomial basis of the higher-level Fock module
- The higher-level wedge-tensor Fock module
- The lower global basis of $U_q^-$ and of a highest weight module
- The upper (form-dual) global basis and the required perfectness of the integral pairing
- Bar invariance, congruence and uniqueness of the lower global basis
- The bar lattice and the divided-power integral lattice of a based module
Used by
- The canonical and quasi-canonical bases need not coincide Counterexample
- Charge reversal and the Fock involution in a small example Example
- Degenerate Ariki decomposition numbers in small rank Example
- Opposite-parabolic Ringel duality on a finite ideal Example
- Projective and simple dual bases in a degenerate cyclotomic block Example
- The four Fock bases in a small two-factor tensor space Example
- Finite type-A tensor Hecke bars and complementary coefficient charts Lemma
- Full finite type-A tensor source upper charts and string leading terms Lemma
- The Fock pairing matches the projective-simple and standard-costandard pairings Lemma
- The local affine-Hecke socle argument for residue translations Lemma
- Type-A tableau central summands are single linkage blocks Lemma
- Sign duality and Ringel duality match the Fock-space involutions Proposition
- Degenerate Specht decomposition numbers are canonical basis coefficients at one Theorem
- Parabolic Kazhdan-Lusztig polynomials give the dual-canonical transition matrix Theorem
- Schur functor images of standard, simple, projective and tilting objects Theorem
- Simples, projectives and tiltings map to the three distinguished Fock bases Theorem
- Standard tableau monomials form a basis of the highest weight Fock submodule Theorem
- The degenerate Ariki categorification theorem Theorem
- The degenerate cyclotomic Hecke G₀ is the dual highest weight module Theorem
- The degenerate cyclotomic Hecke projective K₀ is the highest weight module Theorem
- The highest weight Fock submodule carries the quantum-group global bases Theorem
- The parabolic category-O Grothendieck group is the integral Fock module Theorem
- Type-A parabolic category-O Ringel duality via the opposite parabolic Theorem
Dependency tree · two levels
48 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, The degenerate analogue of Ariki's categorification theorem, Math. Z. 266 (2010) 877-919 (complete 44-page arXiv article) (standard reference, not scraped)
- Jonathan Brundan, Dual canonical bases and Kazhdan-Lusztig polynomials, J. Algebra 306 (2006) 17-46 (complete 29-page arXiv v2 article) (standard reference, not scraped)