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Le but de cette thèse est d'étudier quelques aspects algébriques du problème de quantification par déformation. On considère d'une part la formalité dans le cas des algèbres libres et de l'algèbre de Lie so(3), et on s'intéresse d'autre part à la quantification par déformation pour des structures Hom-algébriques. Suivant le résultat de formalité de Kontsevich en 1997 pour les algèbres symétriques, on étudie dans la première partie de cette thèse les algèbres libres, qui sont un cas particulier d'algèbres enveloppantes, et on montre qu'il n'y a pas formalité en général, sauf dans les cas triviaux. On montre aussi qu'il n'y a pas formalité pour l'algèbre de Lie so(3). Les techniques utilisées sont de type homologiques. On calcule la cohomologie de ces algèbres et on procède à la construction du L-infini-quasi-isomorphisme entre l'algèbre de Lie différentielle graduée des cochaînes de Hochschild munie du crochet de Gerstenhaber et l'algèbre de la cohomologie munie du crochet de Schouten. Dans la seconde partie de ce travail, on utilise un principe de déformation par twist pour les structures Hom-algébriques, pour construire de nouvelles structures de même type, ou encore pour déformer une structure classique en une Hom-structure correspondante à l'aide d'un morphisme d'algèbres. En particulier, on applique ce procédé aux structures de Poisson et aux star-produits de Moyal-Weyl. Par ailleurs, on établit une correspondance entre les algèbres enveloppantes d'algèbres Hom-Lie possédant une structure Hom-coPoisson et les bigèbres Hom-Lie. / This thesis aims to study some algebraic aspects of the deformation quantization problem. On one hand, we consider formality for free algebras and the Lie algebra so(3), and on the other hand we study deformation quantization for Hom-algebraic structures. Following Kontsevich's formality result in 1997 for symmetric algebras, we study in the first part free algebras, which are a particular case of envelopping algebras, and show that there is no formality, except for the trivial cases. We also show that there is no formality for the Lie algebra so(3). The tools used are homological ones. We compute the cohomology of these algebras and proceed to the construction of the L-infinity-quasi-isomorphism between the differential graded Lie algebra of the Hochschild cochains endowed with the Gerstenhaber bracket and the cohomology algebra endowed with the Schouten bracket. In the second part of this work, we use a principle of deformation by twist for Hom-algebraic structures, to construct new structures of the same type, or to deform a classical structure in the corresponding Hom-structure using an algebra morphism. In particular, we apply this method to Poisson structures and Moyal-Weyl star-products. Besides, we establish a correspondance between enveloping algebras of Hom-Lie algebras endowed with a Hom-coPoisson structure and Hom-Lie bialgebras.

<div>We study the Gaudin model associated to Lie algebras of classical types.</div><div><br></div><div>First, we derive explicit formulas for solutions of the Bethe ansatz equations of the Gaudin model associated to the tensor product of one arbitrary finite-dimensional irreducible module and one vector representation for all simple Lie algebras of classical type. We use this result to show that the Bethe Ansatz is complete in any tensor product where all but one factor are vector representations and the evaluation parameters are generic. We also show that except for the type D, the joint spectrum of Gaudin Hamiltonians in such tensor products is simple.</div><div><br></div><div>Second, we define a new stratification of the Grassmannian of N planes. We introduce a new subvariety of Grassmannian, called self-dual Grassmannian, using the connections between self-dual spaces and Gaudin model associated to Lie algebras of types B and C. Then we obtain a stratification of self-dual Grassmannian. </div>

We describe a reproduction procedure which, given a solution of the gl(m|n) Gaudin Bethe ansatz equation associated to a tensor product of polynomial modules, produces a family P of other solutions called the population. <br>To a population we associate a rational pseudodifferential operator R and a superspace W of rational functions. <br><br>We show that if at least one module is typical then the population P is canonically identified with the set of minimal factorizations of R and with the space of full superflags in W. We conjecture that the singular eigenvectors (up to rescaling) of all gl(m|n) Gaudin Hamiltonians are in a bijective correspondence with certain superspaces of rational functions.<br><br>We establish a duality of the non-periodic Gaudin model associated with superalgebra gl(m|n) and the non-periodic Gaudin model associated with algebra gl(k).<br><br>The Hamiltonians of the Gaudin models are given by expansions of a Berezinian of an (m+n) by (m+n) matrix in the case of gl(m|n) <br>and of a column determinant of a k by k matrix in the case of gl(k). We obtain our results by proving Capelli type identities for both cases and comparing the results.<br><br>We study solutions of the Bethe ansatz equations of the non-homogeneous periodic XXX model associated to super Yangian Y(gl(m|n)).<br>To a solution we associate a rational difference operator D and a superspace of rational functions W. We show that the set of complete factorizations of D is in canonical bijection with the variety of superflags in W and that each generic superflag defines a solution of the Bethe ansatz equation. We also give the analogous statements for the quasi-periodic supersymmetric spin chains.<br>

Zugl.: Diss. / Literaturverz. S. [217] - 229.

Cette thèse en trois parties regroupe des travaux de recherches sous la thématiques des symétries sous-jacentes aux systèmes intégrables et des structures algébriques qui les encodent. Une première partie illustre comment les fonctions spéciales que sont les polynômes orthogonaux apparaissent dans la théorie de la représentation des diverses structures algébriques associées à des symétries. La seconde partie se concentre sur une généralisation algébrique de l'opérateur de Heun classique menant à de nouvelles structures algébriques qui trouvent des applications en traitement de signal et dans l'étude des systèmes intégrables. La dernière partie concerne l'élaboration d'un cadre théorique dans le langage de la théorie de l'information algorithmique permettant de poser une définition mathématique de la notion d'émergence. / This thesis in three parts groups research work under the theme of the symmetries underlying integrable systems and the algebraic structures that encodes them. A first part illustrates how orthogonal polynomials, a type of special function, appear in the representation theory of various algebraic structures associated to symmetries. The second part focuses on an algebraic generalization of the classical Heun operator that leads to new algebraic structures with applications in signal processing and in the study of integrable systems. The last part concerns the formulation of a framework in the language of algorithmic information theory the enables a mathematical definition for the notion of emergence.

<p>This dissertation consists of two parts. In the first part, we discuss the boundary and domain wall theories of the generalized quantum double lattice realization of the two-dimensional topological orders based on Hopf algebras. The boundary Hamiltonian and domain wall Hamiltonian are constructed by using Hopf algebra pairings and generalized quantum double. The algebraic data behind the gapped boundary and domain wall are comodule algebras and bicomodule algebras, respectively. The topological excitations in the boundary and domain wall are classified by bimodules over these algebras. Finally, via the Hopf tensor network representation of the quantum many-body states, we solve the ground state of the model in the presence of the boundary and domain wall.</p> <p><br></p> <p>In the second part, we introduce the weak Hopf algebra extension of symmetry, which arises naturally in anyonic quantum systems, and we establish weak Hopf symmetry breaking theory based on the fusion closed set of anyons. We present a thorough investigation of the quantum double model based on weak Hopf algebras, including the topological excitations and ribbon operators, and show that the vacuum sector of the model has weak Hopf symmetry. The gapped boundary and domain wall theories are also established. We show that the gapped boundary is algebraically determined by a comodule algebra, or equivalently, a module algebra, and the gapped domain wall is determined by the bicomodule algebra, or equivalently, a bimodule algebra. We also introduce the weak Hopf tensor network states, by which we solve the weak Hopf quantum double models on closed and open surfaces. Lastly, we discuss the duality of the quantum double phases.</p>

<div>We consider actions of the current Lie algebras $\gl_{n}[t]$ and $\gl_{k}[t]$ on the space $\mathfrak{P}_{kn}$ of polynomials in $kn$ anticommuting variables. The actions depend on parameters $\bar{z}=(z_{1}\lc z_{k})$ and $\bar{\alpha}=(\alpha_{1}\lc\alpha_{n})$, respectively.</div><div>We show that the images of the Bethe algebras $\mathcal{B}_{\bar{\alpha}}^{\langle n \rangle}\subset U(\gl_{n}[t])$ and $\mathcal{B}_{\bar{z}}^{\langle k \rangle}\subset U(\gl_{k}[t])$ under these actions coincide.</div><div></div><div>To prove the statement, we use the Bethe ansatz description of eigenvectors of the Bethe algebras via spaces of quasi-exponentials. We establish an explicit correspondence between the spaces of quasi-exponentials describing eigenvectors of $\mathcal{B}_{\bar{\alpha}}^{\langle n \rangle}$ and the spaces of quasi-exponentials describing eigenvectors of $\mathcal{B}_{\bar{z}}^{\langle k \rangle}$.</div><div></div><div>One particular aspect of the duality of the Bethe algebras is that the Gaudin Hamiltonians exchange with the Dynamical Hamiltonians. We study a similar relation between the trigonometric Gaudin and Dynamical Hamiltonians. In trigonometric Gaudin model, spaces of quasi-exponentials are replaced by spaces of quasi-polynomials. We establish an explicit correspondence between the spaces of quasi-polynomials describing eigenvectors of the trigonometric Gaudin Hamiltonians and the spaces of quasi-exponentials describing eigenvectors of the trigonometric Dynamical Hamiltonians.</div><div></div><div>We also establish the $(\gl_{k},\gl_{n})$-duality for the rational, trigonometric and difference versions of Knizhnik-Zamolodchikov and Dynamical equations.</div>

<p dir="ltr">In this thesis, we develop an algebraic framework for colored, colored connected, semi-grouplike-flavored, and pathlike co-/bi-/Hopf algebras, which are essential in combinatorics, topology, number theory, and physics. Moreover, we introduce and explore simply colored comonoid, which generalises the notion of colored conilpotent coalgebra. The simply colored structure captures the essence of being connected and give unified treatment of all connected co-/bi-algebras. </p><p dir="ltr">As a consequence, we establish precise conditions for the invertibility of characters essential for renormalization in the Connes-Kreimer formulation, supported by examples from these fields. In order to construct antipodes, we discuss formal localization constructions and quantum deformations. These allow to define and explain the appearance of Brown style coactions. We also investigate the relation between pointed coalgebras and color conilpotent coalgebras. </p><p dir="ltr">Using these results, we interpret all relevant coalgebras through categorical constructions, linking the bialgebra structures to Feynman categories and applying our developed theory in this context. This comprehensive framework provides a robust foundation for future research in mathematical physics and algebra.</p>