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Τα σώματα, κυρίως τα μη αντιμεταθετικά, γενικά κατασκευάζονται ως σώματα κλασμάτων δακτυλίων, εντούτοις δεν έχουν όλοι οι δακτύλιοι σώμα κλασμάτων και για δοθέντα δακτύλιο μπορεί να είναι αρκετά δύσκολο να αποφανθούμε αν υπάρχει σώμα κλασμάτων. Στο κεφάλαιο 1 θα αναφέρουμε ορισμένες γενικές παρατηρήσεις πάνω στο είδος των συνθηκών, οι οποίες χαρακτηρίζουν την εμβάπτιση δακτυλίου σε σώμα κλασμάτων και δίνουμε αναγκαίες συνθήκες οι οποίες σχετίζονται με την τάξη των ελεύθερων modules. Στη συνέχεια περιγράφουμε τις συνθήκες του Ore για την εμβάπτιση αυτή, όπου γενικεύεται η αντιμεταθετική περίπτωση. Στο δεύτερο κεφάλαιο εισάγουμε στοιχεία από τη γενική θεωρία τοπολογικών δακτυλίων και modules. Πιο συγκεκριμένα, παρουσιάζονται θεμελιώδεις έννοιες και βασικά αποτελέσματα πάνω στους τοπολογικούς δακτύλιους και τα τοπολογικά σώματα, δίνοντας ιδιαίτερη έμφαση στα στρεβλά σώματα. Πιο συγκεκριμένα εξετάζουμε φραγμένα σύνολα, τοπολογικούς μηδενοδιαιρέτες, τοπολογικά μηδενοδύναμα στοιχεία και minimal τοπολογίες. Αναφέρουμε, επίσης αρκετά παραδείγματα τοπολογιών επί δακτυλίων και modules. Στο κεφάλαιο 3 ορίζουμε διατιμήσεις επί των στρεβλών σωμάτων και ασχολούμαστε με το πρόβλημα ύπαρξης ψευδό-διατιμήσεων σε δακτυλίους και modules. / Fields, especially skew fields, are generally constructed as the field of fractions of some ring, but of course not every ring has a field of fractions and for a given ring it may be quite difficult to decide if a field of fractions exists. In chapter 1 we shall bring some general observations on the kind of conditions to expect and give some necessary conditions relating to the rank of free modules. On the other hand there is the Ore condition generalizing the commutative case. Chapter 2 provides fundamental concepts and basic results on topological rings, modules and especially on skew fields. Under detailed consideration are bounded subsets, topological divisors of zero, topologically nilpotent elements and minimal topologies. There are also many examples of topologies on rings and modules. In chapter 3 we define norms on skew fields and discuss the problem of the existence of real-valued pseudonorms rings and modules.

Dans cette thèse, nous nous sommes intéressés à divers problèmes mettant en oeuvre des structures algébriques de certains anneaux fonctionnels, en particulier dans l'espace H infini des fonctions holomorphes bornées dans le disque unité, dans l'algèbre de Sarason H infini + C et dans C(X,t)={fEC(X) : fot=f}, avec X un espace compact séparé et t une involution topologique sur X. Plus précisément, nous avons caractérisé les idéaux radicaux finiment engendrés dans H infini + C. En second lieu, nous avons démontré que le rang stable absolu de C(X,t) coïncide avec le rang stable Bass et topologique de cette dernière. En dernier lieu, nous nous sommes intéressés au problème de la couronne généralisé dans H infini / In this thesis, we are interested in various problems of algebraic structures of some functional rings, in particular in the space H infinity of bounded analytic functions in the unit disc, in the Sarason algebra H infinity + C and in C(X,t)={fEC(X) : fot=f} with X compact Hausdorff space and t a topological involution on X. More precisely, we have characterized the finitely generated radical ideals in H infinity + C. Secondly, we have demonstrated that the absolute stable rank of C (X, t) coincides with Bass stable rank and topological stable rank. Finally, we are interested in the generalized corona problem in H infinity

The ring of real-valued continuous functions on a completely regular frame L is denoted by RL. As usual, βL denotes the Stone-Cech compactification of ˇ L. In the thesis we study ideals of RL induced by sublocales of βL. We revisit the notion of purity in this ring and use it to characterize basically disconnected frames. The socle of the ring RL is characterized as an ideal induced by the sublocale of βL which is the join of all nowhere dense sublocales of βL. A localic map f : L → M induces a ring homomorphism Rh: RM → RL by composition, where h: M → L is the left adjoint of f. We explore how the sublocale-induced ideals travel along the ring homomorphism Rh, to and fro, via expansion and contraction, respectively. The socle of a ring is the sum of its minimal ideals. In the literature, the socle of RL has been characterized in terms of atoms. Since atoms do not always exist in frames, it is better to express the socle in terms of entities that exist in every frame. In the thesis we characterize the socle as one of the types of ideals induced by sublocales. A classical operator invented by Gillman, Henriksen and Jerison in 1954 is used to create a homomorphism of quantales. The frames in which every cozero element is complemented (they are called P-frames) are characterized in terms of some properties of this quantale homomorphism. Also characterized within the category of quantales are localic analogues of the continuous maps of R.G. Woods that characterize normality in the category of Tychonoff spaces. / Mathematical Sciences / Ph. D. (Mathematics)

We study ideals of pointfree function rings. In particular, we study the lattices of z-ideals and d-ideals of the ring RL of continuous real-valued functions on a completely regular frame L. We show that the lattice of z-ideals is a coherently normal Yosida frame; and the lattice of d-ideals is a coherently normal frame. The lattice of z-ideals is demonstrated to be atly projectable if and only if the ring RL is feebly Baer. On the other hand, the frame of d-ideals is projectable precisely when the frame is cozero-complemented. These ideals give rise to two functors as follows: Sending a frame to the lattice of these ideals is a functorial assignment. We construct a natural transformation between the functors that arise from these assignments. We show that, for a certain collection of frame maps, the functor associated with z-ideals preserves and re ects the property of having a left adjoint. A ring is called a UMP-ring if every maximal ideal in it is the union of the minimal prime ideals it contains. In the penultimate chapter we give several characterisations for the ring RL to be a UMP-ring. We observe, in passing, that if a UMP ring is a Q-algebra, then each of its ideals when viewed as a ring in its own right is a UMP-ring. An example is provided to show that the converse fails. Finally, piggybacking on results in classical rings of continuous functions, we show that, exactly as in C(X), nth roots exist in RL. This is a consequence of an earlier proposition that every reduced f-ring with bounded inversion is the ring of fractions of its bounded part relative to those elements in the bounded part which are units in the bigger ring. We close with a result showing that the frame of open sets of the structure space of RL is isomorphic to L. / Mathematical Sciences / Mathematics / D.Phil. (Mathematics)

The objects of study in this thesis are automorphism groups of free and right-angled Artin groups. Right-angled Artin groups are defined by a presentation where the only relations are commutators of the generating elements. When there are no relations the right-angled-Artin group is a free group and if we take all possible relations we have a free abelian group. We show that if no finite index subgroup of a group $G$ contains a normal subgroup that maps onto $mathbb{Z}$, then every homomorphism from $G$ to the outer automorphism group of a free group has finite image. The above criterion is satisfied by SL$_m(mathbb{Z})$ for $m geq 3$ and, more generally, all irreducible lattices in higher-rank, semisimple Lie groups with finite centre. Given a right-angled Artin group $A_Gamma$ we find an integer $n$, which may be easily read off from the presentation of $A_G$, such that if $m geq 3$ then SL$_m(mathbb{Z})$ is a subgroup of the outer automorphism group of $A_Gamma$ if and only if $m leq n$. More generally, we find criteria to prevent a group from having a homomorphism to the outer automorphism group of $A_Gamma$ with infinite image, and apply this to a large number of irreducible lattices as above. We study the subgroup $IA(A_Gamma)$ of $Aut(A_Gamma)$ that acts trivially on the abelianisation of $A_Gamma$. We show that $IA(A_Gamma)$ is residually torsion-free nilpotent and describe its abelianisation. This is complemented by a survey of previous results concerning the lower central series of $A_Gamma$. One of the commonly used generating sets of $Aut(F_n)$ is the set of Whitehead automorphisms. We describe a geometric method for decomposing an element of $Aut(F_n)$ as a product of Whitehead automorphisms via Stallings' folds. We finish with a brief discussion of the action of $Out(F_n)$ on Culler and Vogtmann's Outer Space. In particular we describe translation lengths of elements with regards to the `non-symmetric Lipschitz metric' on Outer Space.

Parmi les représentations linéaires des groupes de tresses, les représentations de Burau peuvent être construites à partir d’une représentation triviale via une construction introduite par Long en 1994, à l’issue d’une collaboration avec Moody. Cette construction, dite de Long-Moody, permet ainsi de construire des représentations de plus en plus complexes des groupes de tresses. Dans cette thèse, on adopte un point de vue fonctoriel sur cette construction, ce qui permet d’en dégager plus aisément des variantes. De plus, le degré de polynomialité d’un foncteur permet d’en mesurer la complexité. On montre ainsi que la construction Long-Moody définit un foncteur LM, qui augmente le degré de très forte polynomialité. Par ailleurs, on définit des foncteurs analogues pour d’autres familles de groupes telles que les groupes de difféotopie des surfaces et des 3-variétés, les groupes symétriques ou les groupes d’automorphismes des groupes libres. Ils vérifient des propriétés similaires sur la polynomialité. Les foncteurs de Long-Moody fournissent ainsi des coefficients tordus entrant dans le cadre des résultats de stabilité homologique de Randal-Williams et Wahl pour les familles de groupes susmentionnées. On donne enfin un résultat de comparaison entre l’homologie stable à coefficient dans un foncteur F et celle à coefficient dans le foncteur LM(F) obtenu en appliquant un foncteur de Long-Moody. Cette thèse se décompose en trois chapitres. Le premier introduit les foncteurs de Long-Moody pour les groupes de tresses et traite de leur effet sur la polynomialité. Le deuxième traite de la généralisation des foncteurs de Long-Moody pour d’autres familles de groupes. Le dernier chapitre concerne des calculs d’homologie stable pour les groupes de difféotopie. / Among the linear representations of braid groups, Burau representations are recovered from a trivial representation using a construction introduced by Long in 1994, following a collaboration with Moody. This construction, called the Long-Moody construction, thus allows to construct more and more complex representations of braid groups. In this thesis, we have a functorial point of view on this construction, which allows find more easily some variants. Moreover, the degree of polynomiality of a functor measures its complexity. We thus show that the Long-Moody construction defines a functor LM, which increases the degree of polynomiality. Furthermore, we define analogous functors for other families of groups such as mapping class groups of surfaces and 3-manifolds, symmetric groups or automorphism groups of free groups. They satisfy similar properties on the polynomiality. Hence, Long-Moody functors provide twisted coefficients fitting into the framework of the homological stability results of Randal-Williams and Wahl for the afore mentioned families of groups. Finally, we give a comparison result for the stable homology with coefficient given by a functor F and the one with coefficient given by the functor LM(F), obtained applying a Long-Moody functor. This thesis has three chapters. The first one introduces Long-Moody functors for braid groups and deals with their effect on the polynomiality. The first one deals with the generalisation of Long-Moody functors for other families of groups. The last chapter touches on stable homology computations for mapping class group.

We study ideals of pointfree function rings. In particular, we study the lattices of z-ideals and d-ideals of the ring RL of continuous real-valued functions on a completely regular frame L. We show that the lattice of z-ideals is a coherently normal Yosida frame; and the lattice of d-ideals is a coherently normal frame. The lattice of z-ideals is demonstrated to be atly projectable if and only if the ring RL is feebly Baer. On the other hand, the frame of d-ideals is projectable precisely when the frame is cozero-complemented. These ideals give rise to two functors as follows: Sending a frame to the lattice of these ideals is a functorial assignment. We construct a natural transformation between the functors that arise from these assignments. We show that, for a certain collection of frame maps, the functor associated with z-ideals preserves and re ects the property of having a left adjoint. A ring is called a UMP-ring if every maximal ideal in it is the union of the minimal prime ideals it contains. In the penultimate chapter we give several characterisations for the ring RL to be a UMP-ring. We observe, in passing, that if a UMP ring is a Q-algebra, then each of its ideals when viewed as a ring in its own right is a UMP-ring. An example is provided to show that the converse fails. Finally, piggybacking on results in classical rings of continuous functions, we show that, exactly as in C(X), nth roots exist in RL. This is a consequence of an earlier proposition that every reduced f-ring with bounded inversion is the ring of fractions of its bounded part relative to those elements in the bounded part which are units in the bigger ring. We close with a result showing that the frame of open sets of the structure space of RL is isomorphic to L. / Mathematical Sciences / D.Phil. (Mathematics)

Soit k un corps de caractéristique différente de 2 et de 3. Les algèbres de Lie colorées généralisent à la fois les algèbres de Lie et les superalgèbres de Lie. Dans cette thèse on étudie des représentations V d'algèbres de Lie colorées g provenant de structures d'algèbres de Lie colorées sur l'espace vectoriel g⨁V. En premier lieu, on s'intéresse à la structure générale des algèbres de Lie simples de dimension 3 sur k. Puis, on classifie à isomorphisme près les superalgèbres de Lie de dimension finie dont la partie paire est une algèbre de Lie simple de dimension 3. Ensuite, pour un groupe abélien ᴦ et un facteur de commutation ɛ de ᴦ, on développe l'algèbre multilinéaire associée aux espaces vectoriels ᴦ-gradués. Dans ce contexte, les algèbres de Lie colorées jouent le rôle des algèbres de Lie. Ce langage nous permet d'énoncer et prouver un théorème de reconstruction d'une algèbre de Lie colorée ɛ-quadratique g⨁V à partir d'une représentation ɛ-orthogonale V d'une algèbre de Lie colorée ɛ-quadratique g. Ce théorème fait intervenir un invariant qui prend ses valeurs dans la ɛ-algèbre extérieure de V et généralise des résultats de Kostant et Chen-Kang. Puis, on introduit la notion de représentation ɛ-orthogonale spéciale V d'une algèbre de Lie colorée ɛ-quadratique g et on montre qu'elle permet de définir une structure d'algèbre de Lie colorée ɛ-quadratique sur l'espace vectoriel g⨁sl(2,k)⨁V⨂k². Enfin on donne des exemples de représentations ɛ-orthogonales spéciales, notamment des représentations orthogonales spéciales d'algèbres de Lie dont : une famille à un paramètre de représentations de sl(2,k)xsl(2,k) ; la représentation fondamentale de dimension 7 d'une algèbre de Lie de type G₂ ; la représentation spinorielle de dimension 8 d'une algèbre de Lie de type so(7). / Let k be a field of characteristic not 2 or 3. Colour Lie algebras generalise both Lie algebras and Lie superalgebras. In this thesis we study representations V of colour Lie algebras g arising from colour Lie algebras structures on the vector space g⨁V. Firstly, we study the general structure of simple three-dimensional Lie algebras over k. Then, we classify up to isomorphism finite-dimensional Lie superalgebras whose even part is a simple three-dimensional Lie algebra. Next, to an abelian group ᴦ and a commutation factor ɛ of ᴦ, we develop the multilinear algebra associated to ᴦ-graded vector spaces. In this context, colour Lie algebras play the rôle of Lie algebras. This language allows us to state and prove a theorem reconstructing an ɛ-quadratic colour Lie algebra g⨁V from an ɛ-orthogonal representation V of an ɛ-quadratic colour Lie algebra g. This theorem involves an invariant taking its values in the ɛ-exterior algebra of V and generalises results of Kostant and Chen-Kang. We then introduce the notion of a special ɛ-orthogonal representation V of an ɛ-quadratic colour Lie algebra g and show that it allows us to define an ɛ-quadratic colour Lie algebra structure on the vector space g⨁sl(2,k)⨁V⨂k². Finally we give examples of special ɛ-orthogonal representations and in particular examples of special orthogonal representations of Lie algebras amongst which are: a one-parameter family of representations of sl(2,k)xsl(2,k) ; the 7-dimensional fundamental representation of a Lie algebra of type G₂ ; the 8-dimensional spinor representation of a Lie algebra of type so(7).

On étudie dans cette thèse les cycles algébriques sur les variétés Jacobiennes de courbes complexes projectives lisses qui admettent des automorphismes non triviaux. Il s'agit plus précisément d'étudier de nouveaux anneaux tautologiques associés à des groupes d’automorphismes de la courbe. On montre que ces Q-algèbres naturelles de cycles algébriques sur les Jacobiennes se restreignent en des familles de cycles sur certaines sous-variétés spéciales de la Jacobienne et que celles-ci méritent encore le nom d'anneaux tautologiques sur ces sous-variétés. On étudie en détail le cas des courbes hyperelliptiques; situation dans laquelle les algèbres introduites admettent un nombre fini de générateurs, et en particulier sont de dimension finie. On peut alors être très précis dans l'étude des relations entre ces générateurs. Enfin, on montre que ces anneaux tautologiques apparaissent naturellement dans un autre contexte : celui des systèmes linéaires complets sans point de base. / In this thesis we study algebraic cycles on Jacobian varieties of smooth projective complex curves with non trivial automorphisms. More precisely, we introduce new tautological rings associated to groups of automorphisms of the curve. We show that these natural Q-algebras of algebraic cycles on Jacobians induce a good notion of tautological rings on some particular subvarieties of the Jacobian. We then study in detail the case of hyperelliptic curves. In this case, the tautological rings admit a finite number of generators, and in particular are of finite dimension. We can then be very precise when studying the relations between these generators. Finally, we present another situation in which these tautological rings appear: when we consider complete linear series without base point.