arXiv subjects

Jie Du

Publications and source records attributed to Jie Du.

At least 37 records · Page 2Linked to original sources

arXiv2019

The regular representation of $U_v(\mathfrak{gl}_{m|n})$

Using quantum differential operators, we construct a super representation of $U_v(\mathfrak{gl}_{m|n})$ on a certain polynomial superalgebra. We then extend the representation to its formal power series algebra which contains a $U_v(\mathfrak{gl}_{m|n})$-submodule isomorphic to the regular representation of $U_v(\mathfrak{gl}_{m|n})$. In this way, we obtain a presentation of $U_v(\mathfrak{gl}_{m|n})$ by a basis together with explicit multiplication formulas of the basis elements by generators.

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arXiv2018

Polynomial super representations of the hyperalgebra of $\mathfrak{gl}_{m|n}$ at roots of unity

As a homomorphic image of the hyperalgebra $U_{q,R}(m|n)$ associated with the quantum linear supergroup $U_\upsilon(\mathfrak{gl}_{m|n})$, we first give a presentation for the $q$-Schur superalgebra $S_{q,R}(m|n,r)$ over a commutative ring $R$. We then develop a criterion for polynomial supermodules of $U_{q,F}(m|n)$ over a filed $F$ and use this to determine a classification of polynomial irreducible supermodules at roots of unity. This also gives classifications of irreducible $S_{q,F}(m|n,r)$-supermodules for all $r$. As an application when $m=n\geq r$ and motivated by the beautiful work \cite{bru} in the classical (non-quantum) case, we provide a new proof for the Mullineux conjecture related to the irreducible modules over the Hecke algebra $H_{q^2,F}({\mathfrak S}_r)$; see \cite{Br} for a proof without using the super theory.

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arXiv2018

Standard multipartitions and a combinatorial affine Schur-Weyl duality

We introduce the notion of standard multipartitions and establish a one-to-one correspondence between standard multipartitions and irreducible representations with integral weights for the affine Hecke algebra of type A with a parameter q which is not a root of unity. We then extend the correspondence to all Kleshchev multipartitions for Ariki-Koike algebras of integral type. By the affine Schur--Weyl duality, we further extend this to a correspondence between standard multipartitions and Drinfeld multipolynomials of integral type whose associated irreducible polynomial representations completely determine all irreducible polynomial representations for the quantum loop algebra. We will see, in particular, the notion of standard multipartitions gives rise to a combinatorial description of the affine Schur--Weyl duality in terms of a column-reading vs. row reading of residues of a multipartition.

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arXiv2018

Slim cyclotomic q-Schur algebras

We construct a new basis for a slim cyclotomic $q$-Schur algebra $\cysSr$ via symmetric polynomials in Jucys--Murphy operators of the cyclotomic Hecke algebra $\cysHr$. We show that this basis, labelled by matrices, is not the double coset basis when $\cysHr$ is the Hecke algebra of a Coxeter group, but coincides with the double coset basis for the corresponding group algebra, the Hecke algebra at $q=1$. As further applications, we then discuss the cyclotomic Schur--Weyl duality at the integral level. This also includes a category equivalence and a classification of simple objects.

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arXiv2018

Multiplication formulas and semisimplicity for q-Schur superalgebras

We investigate products of certain double cosets for the symmetric group and use the findings to derive some multiplication formulas for q-Schur superalgebras. This gives a combinatorialisation of the relative norm approach developed by the first two authors. We then give several applications of the multiplication formulas, including the matrix representation of the regular representation and a semisimplicity criterion for q-Schur superalgebras. We also construct infinitesimal and little q-Schur superalgebras directly from the multiplication formulas and develop their semisimplicity criteria.

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arXiv2018

Local and global methods in representations of Hecke algebras

This paper aims at developing a "local--global" approach for various types of finite dimensional algebras, especially those related to Hecke algebras. The eventual intention is to apply the methods and applications developed here to the cross-characteristic representation theory of finite groups of Lie type. The authors first review the notions of quasi-hereditary and stratified algebras over a Noetherian commutative ring. They prove that many global properties of these algebras hold if and only if they hold locally at every prime ideal. When the commutative ring is sufficiently good, it is often sufficient to check just the prime ideals of height at most one. These methods are applied to construct certain generalized q-Schur algebras, proving they are often quasi-hereditary (the "good" prime case) but always stratified. Finally, these results are used to prove a triangular decomposition matrix theorem for the modular representations of Hecke algebras at good primes. In the bad prime case, the generalized q-Schur algebras are at least stratified, and a block triangular analogue of the good prime case is proved, where the blocks correspond to Kazhdan-Lusztig cells.

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arXiv2018

The queer q-Schur superalgebra

As a natural generalization quantum Schur algebras associated with the Hecke algebra of the symmetric group, we introduce the quantum Schur superalgebra of type Q associated with the Hecke-Clifford superalgebra, which, by definition, is the endomorphism algebra of the induced module over the Hecke-Clifford superalgebra from certain permutation modules over the Hecke algebra of the symmetric group. We will describe certain integral bases for these superalgebras in terms of matrices and will establish the base change property for them. We will also identify the quantum Schur superalgebra of type Q with the quantum queer Schur superalgebras investigated in the context of quantum queer supergroups and then provide a classification of their irreducible representations over a certain extension of the field of complex rational functions.

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arXiv2016

Stratifying Hecke endomorphism algebras using exact categories

The paper constructs new Hecke endomorphism algebras with a stratified structure. A novel feature of the proof is to approach difficult Ext^1 vanishing conditions by building entire exact category structures in which the analogous vanishing conditions are easier to check. This work is the second in a series aimed at proving a conjecture of the authors published in 1998. The conjecture concerns the enlargement, in a context of Kazhdan-Lusztig cell theory, of Hecke endomorphism algebras related to cross-characteristic representation theory of finite groups of Lie type. This second version corrects some typos and makes other small modifications, some motivated by an anonymous referee and a reader of a prior posting.

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arXiv2016

Multiplicaton formulas and canonical basis for quantum affine gl_n

We will give a representation-theoretic proof for the multiplication formula in the Ringel-Hall algebra ${\frak H}_Δ(n)$ of a cyclic quiver $Δ(n)$ given in \cite[Thm~4.5]{DuFu2015quantum}. As a first application, we see immediately the existence of Hall polynomials for cyclic quivers, a fact established in \cite{Guo1995hallpoly} and \cite{Ringel1993composition}, and derive a recursive formula to compute them. We will further use the formula and the construction of certain monomial base for ${\mathfrak H}_Δ(n)$ given in \cite{DengDuXiao2007generic}, together with the double Ringel--Hall algebra realisation of the quantum loop algebra $U_v(\hat{gl}_n)$ in \cite{DengDuFu2012double}, to develop some algorithms and to compute the canonical basis for $U_v(\hat{gl}_n)^+$. As examples, we will show explicitly the part of the canonical basis associated with modules of Lowey length at most $2$ for the quantum group $U_v(\hat{gl}_n)$.

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arXiv2016

Presenting Hecke endomorphism algebras by Hasse quivers with relations

A Hecke endomorphism algebra is a natural generalisation of the $q$-Schur algebra associated with the symmetric group to a Coxeter group. For Weyl groups, B. Parshall, L. Scott and the first author \cite{DPS,DPS4} investigated the stratification structure of these algebras in order to seek applications to representations of finite groups of Lie type. In this paper we investigate the presentation problem for Hecke endomorphism algebras associated with arbitrary Coxeter groups. Our approach is to present such algebras by quivers with relations. If $R$ is the localisation of $\mathbb Z[q]$ at the polynomials with the constant term 1, the algebra can simply be defined by the so-called idempotent, sandwich and extended braid relations. As applications of this result, we first obtain a presentation of the 0-Hecke endomorphism algebra over $\mathbb{Z}$ and then develop an algorithm for presenting the Hecke endomorphism algebras over $\mathbb Z[q]$ by finding torsion relations. As examples, we determine the torsion relations required for all rank 2 groups and the symmetric group $\mathfrak{S}_4$.

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arXiv2015

Extending Hecke endomorphism algebras at roots of unity

The (Iwahori-)Hecke algebra in the title is a $q$-deformation $\sH$ of the group algebra of a finite Weyl group $W$. The algebra $\sH$ has a natural enlargement to an endomorphism algebra $\sA=\End_\sH(\sT)$ where $\sT$ is a $q$-permutation module. In type $A_n$ (i.e., $W\cong {\mathfrak S}_{n+1}$), the algebra $\sA$ is a $q$-Schur algebra which is quasi-hereditary and plays an important role in the modular representation of the finite groups of Lie type. In other types, $\sA$ is not always quasi-hereditary, but the authors conjectured 20 year ago that $\sT$ can be enlarged to an $\sH$-module $\sT^+$ so that $\sA^+=\End_\sH(\sT^+)$ is at least standardly stratified, a weaker condition than being quasi-hereditary, but with "strata" corresponding to Kazhdan-Lusztig two-sided cells. The main result of this paper is a "local" version of this conjecture in the equal parameter case, viewing $\sH$ as defined over ${\mathbb Z}[t,t^{-1}]$, with the localization at a prime ideal generated by a cyclotomic polynomial $Φ_{2e}(t)$, $e\not=2$. The proof uses the theory of rational Cherednik algebras (also known as RDAHAs) over similar localizations of ${\mathbb C}[t,t^{-1}]$. In future paper, the authors expect to apply these results to prove global versions of the conjecture, at least in the equal parameter case with bad primes excluded.

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arXiv2015

Canonical bases for the quantum linear supergroups

We give a combinatorial construction for the canonical bases of the $\pm$-parts of the quantum enveloping superalgebra $\bfU(\mathfrak{gl}_{m|n})$ and discuss their relationship with the Kazhdan-Lusztig bases for the quantum Schur superalgebras $\bsS(m|n,r)$ introduced in \cite{DR}. We will also extend this relationship to the induced bases for simple polynomial representations of $\bfU(\mathfrak{gl}_{m|n})$.

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arXiv2014

The Integral quantum loop algebra of $\mathfrak{gl}_n$

We will construct the Lusztig form for the quantum loop algebra of $\mathfrak{gl}_n$ by proving the conjecture \cite[3.8.6]{DDF} and establish partially the Schur--Weyl duality at the integral level in this case. We will also investigate the integral form of the modified quantum affine $\mathfrak{gl}_n$ by introducing an affine stabilisation property and will lift the canonical bases from affine quantum Schur algebras to a canonical basis for this integral form. As an application of our theory, we will also discuss the integral form of the modified extended quantum affine $\mathfrak{sl}_n$ and construct its canonical basis to verify a conjecture of Lusztig in this case.

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arXiv2014

Presenting queer Schur superalgebras

Associated to the two types of finite dimensional simple superalgebras, there are the general linear Lie superalgebra and the queer Lie superalgebra. The universal enveloping algebras of these Lie superalgebras act on the tensor spaces of the natural representations and, thus, define certain finite dimensional quotients, the Schur superalgebras and the queer Schur superalgebra. In this paper, we introduce the quantum analogue of the queer Schur superalgebra and investigate the presentation problem for both the queer Schur superalgebra and its quantum analogue.

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arXiv2013

Quantum affine $\frak{gl}_n$ via Hecke algebras

We use the Hecke algebras of affine symmetric groups and their associated Schur algebras to construct a new algebra through a basis, and a set of generators and explicit multiplication formulas of basis elements by generators. We prove that this algebra is isomorphic to the quantum enveloping algebra of the loop algebra of $\mathfrak {gl}_n$. Though this construction is motivated by the work \cite{BLM} by Beilinson--Lusztig--MacPherson for quantum $\frak{gl}_n$, our approach is purely algebraic and combinatorial, independent of the geometric method which seems to work only for quantum $\mathfrak{gl}_n$ and quantum affine $\mathfrak{sl}_n$. As an application, we discover a presentation of the Ringel--Hall algebra of a cyclic quiver by semisimple generators and their multiplications by the defining basis elements.

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arXiv2013

A realisation of the quantum linear superalgebra

We reconstruct the quantum enveloping superalgebra ${\bf U}(\mathfrak{gl}_{m|n})$ over $\mathbb Q(v)$ via (finite dimensional) quantum Schur superalgebras. In particular, we obtain a new basis containing the standard generators of ${\bf U}(\mathfrak{gl}_{m|n})$ and explicit multiplication formulas between the generators and an arbitrary basis element.

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arXiv2013

Irreducible representations of q-Schur superalgebras at a root of unity

Under the assumption that the quantum parameter $q$ is an $l$-th primitive root of unity with $l$ odd in a field $F$ of characteristic 0 and $m+n\geq r$, we obtained a complete classification of irreducible modules of the $q$-Schur superalgebra introduced H. Rui and the first Author.

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arXiv2012

Small Representations for Affine q-Schur Algebras

When the parameter $q\in\mathbb C^*$ is not a root of unity, simple modules of affine $q$-Schur algebras have been classified in terms of Frenkel--Mukhin's dominant Drinfeld polynomials (\cite[4.6.8]{DDF}). We compute these Drinfeld polynomials associated with the simple modules of an affine $q$-Schur algebra which come from the simple modules of the corresponding $q$-Schur algebra via the evaluation maps.

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