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The present dissertation consists of four interconnected projects. In the first, we introduce and study what we call factorizable module algebras. These are $U_q(\mathfrak{g})$-module algebras $A$ which factor, potentially after localization, as the tensor product of the subalgebra $A^+$ of highest weight vectors of $A$ and a copy of the quantum coordinate algebra $\mathcal{A}_q[U]$, where $U$ is a maximal unipotent subgroup of $G$, a semisimple Lie group whose Lie algebra is $\mathfrak{g}$. The class of factorizable module algebras is surprisingly rich, in particular including the quantum coordinate algebras $\mathcal{A}_q[Mat_{m,n}]$, $\mathcal{A}_q[G]$ and $\mathcal{A}_q[G/U]$. It is closed under the braided tensor product and, moreover, the subalgebra $A^+$ of each such $A$ is naturally a module algebra over the quantization of $\mathfrak{g}^*$, the Lie algebra of the Poisson dual group $G^*$. The aforementioned examples of factorizable module algebras all possess dual canonical bases which behave nicely with respect to factorization $A=A^+\otimes \mathcal{A}_q[U]$. We expect the same is true for many other members of this class, including braided tensor products of such. To facilitate such a construction in tensor products, we propose an axiomatic framework of based modules which, in particular, vastly generalizes Lusztig's notion of based modules. We argue that all of the aforementioned $U_q(\mathfrak{g})$-module algebras (and many others) with their dual canonical bases are included, along with their tensor products. One of the central objects of study emerging from our generalization of Lusztig's based modules is a new (very canonical) basis $\mathcal{B}^{\diamond n}$ in the $n$-th braided tensor power $\mathcal{A}_q[G/U]$. We argue (yet conjecturally) that $\mathcal{A}_q[G/U]^{\underline{\otimes}n}$ has a quantum cluster structure and conjecture that the expected cluster structure structure on $\mathcal{A}_q[G/U]^{\underline{\otimes}n}$ is completely controlled by the real elements of our canonical basis $\mathcal{B}^{\diamond n}$. Finally, in order to partially explain the monoidal structures appearing above, we provide an axiomatic framework to construct examples of bialgebroids of Sweedler type. In particular, we describe a bialgebroid structure on $\mathfrak{u}_q(\mathfrak{g})\rtimes\mathbb{Q} C_2$, where $\mathfrak{u}_q(\mathfrak{g})$ is the small quantum group and $C_2$ is the cyclic group of order two. This dissertation contains previously published co-authored material.

Neste trabalho introduzimos uma nova classe de álgebra de conglomerado com coeficientes do tipo Dynkin A_n, a qual denominaremos álgebra c-conglomerada. Desenvolvemos a teoria dos c-frisos, a qual foi introduzida por Matte, Desloges e Sanchez, para o estudo das propriedades combinatórias da álgebra c-conglomerada. Usando c-frisos, obtemos uma fórmula explícita para as variáveis de conglomerado de uma álgebra c-conglomerada que explica simultaneamente o fenômeno de Laurent e a positividade. Interpretamos geometricamente a álgebra c-conglomerada em termos de triangulações de polígonos, em que triangulações correspondem aos conglomerados e diagonais correspondem às variáveis de conglomerado de uma álgebra c-conglomerada. Além disso, generalizamos a aplicação de Caldero-Chapoton e utilizamos esta versão mais geral para obter as variáveis de conglomerado de uma álgebra c-conglomerada em função dos objetos indecomponíveis da categoria de conglomerado do tipo A_n. / In this work we introduce a new class of cluster algebra with coefficients of Dynkin type A_n, which we call c-cluster algebra. In order to study the combinatorics of the c-cluster algebra, we develop the theory of c-friezes introduced by Matte, Desloges and Sanchez. Using c-friezes, we give an explicit formula for all cluster variables of a c-cluster algebra, which explains simultaneously the Laurent phenomenon and the positivity. A c-cluster algebra also has a geometric interpretation in terms of triangulations of a polygon, where clusters are in one-to-one correspondence with triangulations and the cluster variables are in one-to-one correspondence with diagonals. Finally, we give a generalization of the Caldero-Chapoton map which we use to obtain the cluster variables of a c-cluster algebra in terms of the indecomposable objects of the cluster category of type A_n.

Cluster categories, introduced by Buan–Marsh–Reineke–Reiten–Todorov and later generalised by Amiot, are certain 2-Calabi–Yau triangulated categories that model the combinatorics of cluster algebras without frozen variables. When frozen variables do occur, it is natural to try to model the cluster combinatorics via a Frobenius category, with the indecomposable projective-injective objects corresponding to these special variables. Amiot–Iyama–Reiten show how Frobenius categories admitting (d-1)-cluster-tilting objects arise naturally from the data of a Noetherian bimodule d-Calabi–Yau algebra A and an idempotent e of A such that A/< e > is finite dimensional. In this work, we observe that this phenomenon still occurs under the weaker assumption that A and A^op are internally d-Calabi–Yau with respect to e; this new definition allows the d-Calabi–Yau property to fail in a way controlled by e. Under either set of assumptions, the algebra B=eAe is Iwanaga–Gorenstein, and eA is a cluster-tilting object in the Frobenius category GP(B) of Gorenstein projective B-modules. Geiß–Leclerc–Schröer define a class of cluster algebras that are, by construction, modelled by certain Frobenius subcategories Sub(Q_J) of module categories over preprojective algebras. Buan–Iyama–Reiten–Smith prove that the endomorphism algebra of a cluster-tilting object in one of these categories is a frozen Jacobian algebra. Following Keller–Reiten, we observe that such algebras are internally 3-Calabi–Yau with respect to the idempotent corresponding to the frozen vertices, thus obtaining a large class of examples of such algebras. Geiß–Leclerc–Schröer also attach, via an algebraic homogenization procedure, a second cluster algebra to each category Sub(Q_J), by adding more frozen variables. We describe how to compute the quiver of a seed in this cluster algebra via approximation theory in the category Sub(Q_J); our alternative construction has the advantage that arrows between the frozen vertices appear naturally. We write down a potential on this enlarged quiver, and conjecture that the resulting frozen Jacobian algebra A and its opposite are internally 3-Calabi–Yau. If true, the algebra may be realised as the endomorphism algebra of a cluster-tilting object in a Frobenius category GP(B) as above. We further conjecture that GP(B) is stably 2-Calabi–Yau, in which case it would provide a categorification of this second cluster algebra.

Inspired by work of Hubery [Hub] and Fomin, Shapiro and Thurston [FST06] related to cluster algebras, we construct a bijection between certain curves on a cylinder and the string modules over a path algebra of type Ãn. We show that under this bijection irreducible maps and the Auslander-Reiten translation have a geometric interpretation. Furthermore we prove that the dimension of extension groups can be expressed in terms of intersection numbers. Finally we explain the connection to cluster algebras and apply our results to describe the exchange graph in type Ãn. / Angeregt durch Arbeiten zu Cluster-Algebren von Hubery [Hub] und Fomin, Shapiro und Thurston [FST06] konstruieren wir eine Bijektion zwischen gewissen Kurven auf einem Zylinder und den Fadenmoduln über einer Wege-Algebra vom Typ Ãn. Wir zeigen, daß unter dieser Bijektion sowohl irreduzible Abbildungen als auch die Auslander-Reiten-Verschiebung eine geometrische Interpretation haben. Weiterhin beweisen wir, daß sich die Dimension der Erweiterungsgruppen mittels Anzahlen von Schnittpunkten ausdrücken läßt. Schließlich erklären wir die Verbindung zu Cluster-Algebren und verwenden unsere Ergebnisse um den Austauschgraph im Typ Ãn zu beschreiben.

Inspired by work of Hubery [Hub] and Fomin, Shapiro and Thurston [FST06] related to cluster algebras, we construct a bijection between certain curves on a cylinder and the string modules over a path algebra of type Ãn. We show that under this bijection irreducible maps and the Auslander-Reiten translation have a geometric interpretation. Furthermore we prove that the dimension of extension groups can be expressed in terms of intersection numbers. Finally we explain the connection to cluster algebras and apply our results to describe the exchange graph in type Ãn. / Angeregt durch Arbeiten zu Cluster-Algebren von Hubery [Hub] und Fomin, Shapiro und Thurston [FST06] konstruieren wir eine Bijektion zwischen gewissen Kurven auf einem Zylinder und den Fadenmoduln über einer Wege-Algebra vom Typ Ãn. Wir zeigen, daß unter dieser Bijektion sowohl irreduzible Abbildungen als auch die Auslander-Reiten-Verschiebung eine geometrische Interpretation haben. Weiterhin beweisen wir, daß sich die Dimension der Erweiterungsgruppen mittels Anzahlen von Schnittpunkten ausdrücken läßt. Schließlich erklären wir die Verbindung zu Cluster-Algebren und verwenden unsere Ergebnisse um den Austauschgraph im Typ Ãn zu beschreiben.

Inspired by Happel's question, whether the exchange graph and the simplicial complex of tilting modules over a quiver algebra are independent from the multiplicities of multiple arrows in the quiver, we study quantitative aspects of Fomin and Zelevinsky's quiver mutation rule. Our results turn out to be very useful in the mutation-infinite case for understanding combinatorial structures as the cluster exchange graph or the simplicial complex of tilting modules, which are governed by quiver mutation. Using a class of quivers we call forks we can show that any such quiver yields a tree in the exchange graph. This allows us to provide a good global description of the exchange graphs of arbitrary mutation-infinite quivers. In particular we show that the exchange graph of an acyclic quiver is a tree if (and in fact only if) any two vertices are connected by at least two arrows. Furthermore we give classification results for the simplicial complexes and thereby obtain a partial positive answer to Happel's question. Another consequence of our findings is a confirmation of Unger's conjecture about the infinite number of components of the tilting exchange graph in all but finitely many cases. Finally we generalise and conceptualise our results by introducing what we call "polynomial quivers", stating several conjectures about "polynomial quiver mutation", and giving proofs in special cases.

Inspired by Happel's question, whether the exchange graph and the simplicial complex of tilting modules over a quiver algebra are independent from the multiplicities of multiple arrows in the quiver, we study quantitative aspects of Fomin and Zelevinsky's quiver mutation rule. Our results turn out to be very useful in the mutation-infinite case for understanding combinatorial structures as the cluster exchange graph or the simplicial complex of tilting modules, which are governed by quiver mutation. Using a class of quivers we call forks we can show that any such quiver yields a tree in the exchange graph. This allows us to provide a good global description of the exchange graphs of arbitrary mutation-infinite quivers. In particular we show that the exchange graph of an acyclic quiver is a tree if (and in fact only if) any two vertices are connected by at least two arrows. Furthermore we give classification results for the simplicial complexes and thereby obtain a partial positive answer to Happel's question. Another consequence of our findings is a confirmation of Unger's conjecture about the infinite number of components of the tilting exchange graph in all but finitely many cases. Finally we generalise and conceptualise our results by introducing what we call "polynomial quivers", stating several conjectures about "polynomial quiver mutation", and giving proofs in special cases.