Abstracts of publications and preprints


Representations of twisted Yangians of types B, C, D: II pdf :  We continue the study of finite-dimensional irreducible representations of twisted Yangians associated to symmetric pairs of types B, C and D, with focus on those of types BI, CII and DI. After establishing that, for all twisted Yangians of these types, the highest weight of such a module necessarily satisfies a certain set of relations, we classify the finite-dimensional irreducible representations of twisted Yangians for the pairs (soN,soN-2 + so2) and (so2n+1,so2n).

Equivalences between three presentations of orthogonal and symplectic Yangians pdf :  We prove the equivalence of two presentations of the Yangian of a simple Lie algebra and we also show the equivalence with a third presentation when the Lie algebra is either orthogonal or symplectic. As an application, we obtain an explicit correspondence between the two versions of the classification theorem of finite-dimensional irreducible modules for orthogonal and symplectic Yangians.

Representations of twisted Yangians of types B, C, D: I pdf:  We develop a theory of highest weight representations for twisted Yangians of types B, C, D and we classify the finite-dimensional irreducible representations of twisted Yangians associated to symmetric pairs of types CI, DIII and BCD0.

Local Weyl modules and cyclicity of tensor products for Yangians pdf:  We provide a sufficient condition for the cyclicity of an ordered tensor product of fundamental representations of a Yangian associated to a simple Lie algebra. When this Lie algebra is classical, we make the cyclicity condition concrete, which leads to an irreducibility criterion for the ordered tensor product. We show that every local Weyl module is isomorphic to an ordered tensor product of fundamental representations of the Yangian.

Deformed double current algebras of sl(2) and sl(3) (in preparation) :  We propose two definitions of deformed double current algebras associated to sl(2) and sl(3) and prove their equivalence. This is a companion paper to our article On deformed double current algebras where we assume that the rank of the simple Lie algebra is at least 3.

Twisted Yangians of small rank pdf:  We establish isomorphisms between certain twisted Yangians of rank one or two introduced in the paper "Yangians for symmetric pairs of types B,C,D" and corresponding twisted Yangians for symmetric pairs of types AI and AII introduced originally by G. Olshanski.

Twisted Yangians for symmetric pairs of types B,C,D pdf:  We study coideal subalgebras of the extended Yangians of type B,C,D associated to appropriate solutions of the reflection equation. Those subalgebras can be viewed as twisted Yangians for the symmetric pairs of type BDI, CI, CII and DIII in Cartan's classification.

On deformed double current algebras of simple Lie algebras pdf:  We prove the equivalence of two definitions of deformed double current algebras associated to a semisimple Lie algebra. One definition was proposed by myself in Quantum algebras and quivers by considering a certain degeneration of an affine Yangian, the other one arose in recent work of V. Toledano Laredo and Y. Yang on elliptic Casimir connections. We also construct a certain central element and prove that, in type A and for certain values of the deformation parameters, the center of a deformed double current algebra contains two polynomial rings in infinitely many variables.

From twisted quantum loop algebras to twisted Yangians pdf :  We prove how the Yangian of gl_n in its RTT presentation and how Olshanski's twisted Yangians for the orthogonal and symplectic Lie algebras can be obtained by a degeneration process from quantum loop algebras and some of their twisted analogues.

Almost cellular algebras pdf:  We obtain results on algebras which have all the properties of cellular algebras except for the existence of a certain anti-involution. We apply them to the quantum walled Brauer-Clifford superalgebras studied in the next paper below.

Quantum Walled Brauer-Clifford Superalgebras pdf:  We introduce a family of associative superalgebras which are analogues of the quantum walled Brauer algebras and are q-deformations of the walled Brauer superalgebras. These new superalgebras are described explicitly via generators and relations. We show that they are isomorphic to the centralizer algebras of the action of quantum superalgebras of type Q on mixed tensor spaces. We obtain for them a diagrammatic presentation and prove that they are almost cellular. We are also led to define q-Schur superalgebras of type Q and prove for them a super analog of a classical result for q-Schur algebras using a quantization of the algebra of regular functions on the space of supermatrices of type Q.

Vertex operators for Yangians of Kac-Moody algebras (in preparation):  We construct vertex operator representations for Yangians of simply-laced Kac-Moody algebras and use these, along with the coproduct in the preprint below, to prove the PBW property of those Yangians.

Coproduct for Yangians of Kac-Moody algebras pdf:  We construct a new coproduct on (completed) Yangians associated to affine Kac-Moody algebras. We also produce a presentation of Yangians of symmetrizable Kac-Moody algebras which may be of independent interest.

Quantum superalgebras of type P (in preparation) :  We introduce a quantized enveloping superalgebra of type P similar to Olshanski's quantized enveloping superalgebra of type Q. It is defined via an RTT-relation, using a suitable solution of the quantum Yang-Baxter equation.

Twisted Yangians, twisted quantum loop algebras and affine Hecke algebras of type BC pdf :  We study twisted Yangians of type AIII which have appeared in the literature under the name of reflection algebras. They admit q-versions which are new twisted quantum loop algebras. We explain how these can be defined equivalently either via the reflection equation or as coideal subalgebras of Yangians of gl_n (resp. quantum loop algebras of gl_n). The connection with affine Hecke algebras of type BC comes from a functor of Schur-Weyl type between their module categories.

From quantum loop algebras to Yangians pdf :   The main purpose of this note is to give a proof of a statement of V. Drinfeld regarding Yangians and quantum loop algebras, namely how the former can be constructed as limit forms of the latter. We also apply the same ideas to twisted quantum loop algebras to recover the (non-twisted) Yangians.

Twisted affine Lie superalgebra of type Q and quantization of its enveloping superalgebra pdf :   We introduce a new quantum group which is a quantization of the enveloping superalgebra of a twisted affine Lie superalgebra of type Q. We study generators and relations for superalgebras in the finite and twisted affine case, and also universal central extensions. Afterwards, we apply the FRT formalism to a certain solution of the quantum Yang-Baxter equation to define that new quantum group and we study some of its properties. We construct a functor of Schur-Weyl type which connects it to affine Hecke-Clifford algebras and prove that it provides an equivalence between two categories of modules.

Central extensions of matrix Lie superalgebras over Z/2Z-graded algebras pdf :   We study central extensions of the Lie superalgebra sl_n(A) when A is a Z/2Z-graded superalgebra over a commutative ring K. Steinberg Lie superalgebras and their central extensions play an essential role. We use a Z/2Z-graded version of cyclic homology to study the center of the extensions in question.

Double affine Lie algebras and finite groups pdf :   We begin to study the Lie theoretical analogs of symplectic reflection algebras for a finite cyclic group G, which we call ``cyclic double affine Lie algebra''. We focus on type A : in the finite (resp. affine, double affine) case, we prove that these structures are finite (resp. affine, toroidal) type Lie algebras, but the gradings differ. The case which is essentially new is the smash product of C[u,v] with G.  We describe its universal central extensions and start the study of its representation theory, in particular of its highest weight integrable modules and Weyl modules. We also consider the first Weyl algebra A_1 instead of the polynomial ring C[u,v], and, more generally, a rank one rational Cherednik algebra.  We study quasi-finite highest weight representations of these Lie algebras.

Quantum algebras and quivers pdf :   This paper starts with some general results about Lie algebras of type A over quadratic algebras and then suggests a definition of deformed double current algebras for any simple Lie algebra. To a quiver Q, we associate a new family of quantum algebras which are deformationZ/2Zs of the enveloping algebra of a Lie algebra slightly larger than the universal central extension of sl_n defined over the preprojective algebra of Q. We study some of their structural properties, obtain a Schur-Weyl functor connecting them to deformed preprojective algebras for wreath products,  prove that they have the PBW property when Q is an affine Dynkin quiver and we relate them to the quantum algebras studied in our previous paper. We are able to construct reflection functors between categories of modules over our quantum quiver algebras for different values of the deformation parameters.  

Quantum algebras and symplectic reflection algebras for wreath products pdf :   We generalize the results of the two papers immediately below to the case of symplectic reflection algebras for wreath products of finite subgroups G of SL_2(C). We introduce a new family of algebras called G-deformed double current algebras (G-DDCAs) and construct for them Poincare-Birkhoff-Witt bases to show that they are flat deformations of the enveloping algebra of an enlargement of the universal central extension of sl_n over the smash product of C[u,v] with G. When G is a cyclic group, we are able to connect G-DDCAs to Yangians.


Affine Yangians and deformed double current algebras in type A pdf :   We focus on the structure of the algebras in question. We construct Poincare-Birkhoff-Witt bases for affine Yangians and deformed double current algebras (DDCAs) using a module obtained by applying the Schur-Weyl functor to a Cherednik algebra, we explain how to obtain them via a limit procedure starting from quantum toroidal algebras, and we show that they are deformations of matrix W1+oo-algebras. We are also able to establish the equivalence of three different definitions of DDCAs.


Cherednik algebras and Yangians pdf :   We construct a functor F from the category of modules over a trigonometric Cherednik algebra of type gl_l to a certain category of modules over an affine Yangian for sl_n. This extends the classical Schur-Weyl construction. We give a sufficient condition for this functor to be an equivalence. Our main goal, which is achieved in the second part, was to identify the Schur-Weyl dual of a rational Cherednik algebra for the symmetric group S_l: the answer is given by a new family of algebras that we have called deformed polynomial double loop algebras (deformed double current algebras in the subsequent papers).

On the Category O for Rational Cherednik Algebras pdf :   This article provides an exhaustive study of the category O of modules over the rational Cherednik algebra Hk (associated to a finite complex reflection group W) and of the functor KZ from O to the category mod-H of finitely generated modules over a finite Hecke algebra H. In the first section, we study the highest weight structure of the category O; many results are valid over quite general base rings. The following two sections introduce different duality functors between Cherednik algebras, study homological properties of O and provide a construction of the semi-regular bimodule of Hk
 
The three main results of this paper concern the functor KZ

 - H is isomorphic to EndH(PKZ)opp where PKZ is a certain projective object in O
 
 - Double-centralizer theorem: The map HomH(M,Q) --->HomH(KZ(M),KZ(Q)) induced by the functor KZ is an isomorphism if M,Q are in O and Q is projective. 
 
 - If the parameter k is just one positive real number and W is a Weyl group, then the image of a Verma module under KZ is isomorphic to the cell (standard) module of H corresponding to the same irreducible representation of W as the Verma module.

Projective Modules in the Category O for the Cherednik algebra pdf :   We study the category O of a rational Cherednik algebra H. The first result is that O has enough projective objects.  Our main theorem states that O is a highest weight category with duality; in particular, projective modules admit filtrations whose successive subquotients are standard modules. This last property is derived from a quite explicit construction of projectives in O. From our main result, it follows that an analog of the BGG-reciprocity formula, which connects projective, standard and simple modules, holds in O.  Finally, we provide an upper bound on the cohomological dimension of O

Embeddings of symmetric varieties pdf :   The construction of the enveloping semigroup of a semisimple algebraic group G, due to E.B. Vinberg, is generalized to the case of a symmetric variety G/K, K being the fixed-point subgroup of an involution of G. We construct a variety Env(G/K) which is an affine spherical embedding of G/K. We use the language of colored cones and study some properties of this enveloping variety.  We recall a few facts about the wonderful compactification of the adjoint Gad/Kad due to C. De Concini and C. Procesi, and we establish two connections between it and Env(G/K): first, Env(G/K) is a fiber product, over an affine toric variety, of an affine space with the normalization of a multi-cone over the compactification of Gad/Kad; secondly, under a certain assumption on G/K, we realize this compactification as a geometric quotient of an open subvariety of Env(G/K).  


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