Koszul algebras and Donaldson-Thomas invariants

For a given symmetric quiver $Q$, we define a supercommutative quadratic algebra $\mathcal{A}_Q$ whose Poincar\'e series is related to the motivic generating function of $Q$ by a simple change of variables. The Koszul duality between supercommutative algebras and Lie superalgebras assigns to the algebra $\mathcal{A}_Q$ its Koszul dual Lie superalgebra $\mathfrak{g}_Q$. We prove that the motivic Donaldson-Thomas invariants of the quiver $Q$ may be computed using the Poincar\'e series of a certain Lie subalgebra of $\mathfrak{g}_Q$ that can be described, using an action of the first Weyl algebra on $\mathfrak{g}_Q$, as the kernel of the operator $\partial_t$. This gives a new proof of positivity for motivic Donaldson--Thomas invariants. In addition, we prove that the algebra $\mathcal{A}_Q$ is numerically Koszul for every symmetric quiver $Q$ and conjecture that it is in fact Koszul; we also prove this conjecture for quivers of a certain class.Comment: 25 pages, the main result on DT invariants of symmetric quivers is now not conditional on Koszulnes

Propriedades homológicas de finitude

Orientador: Dessislava Hristova KochloukovaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação CientíficaResumo: Consideramos problemas nas teorias de grupos discretos, álgebras de Lie e grupos pro-p. Apresentamos resultados relacionados sobretudo a propriedades homológicas de finitude de tais estruturas algébricas. Primeiramente, discutimos Sigma-invariantes de produtos entrelaçados de grupos discretos. Descrevemos completamente o invariante Sigma1, relacionado à herança por subgrupos da propriedade de ser finitamente gerado, e descrevemos parcialmente o invariante Sigma2, relacionado à herança por subgrupos da propriedade de admitir uma apresentação finita. Aplicamos tais resultados ao estudo de números de Reidemeister de isomorfismos de certos produtos entrelaçados. Na sequência definimos e estudamos uma versão da construção de comutatividade fraca de Sidki na categoria de álgebras de Lie sobre um corpo de característica diferente de dois. Tal construção pode ser vista como um funtor que recebe uma álgebra de Lie g e retorna um certo quociente chi(g) da soma livre de duas cópias isomorfas de g. Demonstramos resultados sobre a preservação de certas propriedades algébricas por tal funtor e mostramos que o multiplicador de Schur de g é um subquociente de chi(g). Mostramos em particular que, para uma álgebra de Lie livre g de posto ao menos três, chi(g) é finitamente apresentável mas não é de tipo FP3 , e tem dimensão cohomológica infinita. Por fim, consideramos também uma versão da construção de comutatividade fraca na categoria de grupos pro-p para um número primo fixado p. Mostramos que tal construção também preserva diversas propriedades algébricas, como ocorre nos casos de grupos discretos e álgebras de Lie. Para tanto estudamos também produtos subdiretos de grupos pro-p; em particular demonstramos uma versão do Teorema (n ? 1) ? n ? (n + 1)Abstract: We consider problems in the theories of discrete groups, Lie algebras, and pro-p groups. We present results related mainly to homological finiteness properties of such algebraic structures. First, we discuss Sigma-invariants of wreath products of discrete groups. We give a complete description of the Sigma1-invariant, which is related to the inheritance of the property of being finitely generated by subgroups. We also describe partially the invariant Sigma2, which is related to the inheritance of finite presentability by subgroups. We apply such results in the study of Reidemeister numbers of isomorphisms of certain wreath products. Then we define and study a version of Sidki¿s weak commutativity construction in the category of Lie algebras over a field whose characteristic is not two. Such construction can be seen as a functor that receives a Lie algebra g and returns a certain quotient chi(g) of the free sum of two isomorphic copies of g. We prove some results on the preservation of certain algebraic properties by this functor, and we show that the Schur multiplier of g is a subquotient of chi(g). We show in particular that, for a free Lie algebra g with at least three free generators, chi(g) is finitely presentable but not of type FP3 , and has infinite cohomological dimension. Finally, we also consider a version of the weak commutativity construction in the category of pro-p groups for a fixed prime number p. We show that such construction also preserves several algebraic properties, as occurs in the cases of discrete groups and Lie algebras. To this end, we also study subdirect products of pro-p groups. In particular we prove a version of the (n ? 1) ? n ? (n + 1) TheoremDoutoradoMatematicaDoutor em Matemática2015/22064-6; 2016/24778-9FAPES

Liftings of Nichols algebras of diagonal type III. Cartan type G2G_2

We complete the classification of Hopf algebras whose infinitesimal braiding is a principal Yetter-Drinfeld realization of a braided vector space of Cartan type $G_2$ over a cosemisimple Hopf algebra. We develop a general formula for a class of liftings in which the quantum Serre relations hold. We give a detailed explanation of the procedure for finding the relations, based on the recent work of Andruskiewitsch, Angiono and Rossi Bertone.Comment: 54 pages; including an appendix. Final version, to appear in J. Algebr

Structure Analysis of the Pohlmeyer-Rehren Lie Algebra and Adaptations of the Hall Algorithm to Non-Free Graded Lie Algebras

The Pohlmeyer-Rehren Lie algebra $\mathfrak{g}$ is an infinite-dimensional $\mathbb{Z}$-graded Lie algebra that was discovered in the context of string quantization in $d$-dimensional spacetime by K. Pohlmeyer and his collaborators and has more recently been reformulated in terms of the Euler-idempotents of the shuffle Hopf algebra. This thesis is divided into two major parts. In the first part, the structure theory of $\mathfrak{g}$ is discussed. $\mathfrak{g}_0$, the stratum of degree zero, is isomorphic to the classical Lie algebra $\mathfrak{so}(d,\mathbb{C})$. Now, each stratum is considered as a $\mathfrak{g}_0$-module, and a formula for the number of irreducible $\mathfrak{g}_0$-modules of each highest weight that occur is given. It is also shown that $\mathfrak{g}$ is not a Kac-Moody algebra. Based on computer-aided calculations, $\mathfrak{g}$ is conjectured to be generated by the strata of degrees $0$ and $1$, but not freely. In an effort to classify the relations, in the second part, the Philip Hall algorithm that iteratively lists (linear) basis elements of a Lie algebra $L(X)$ freely generated by a finite set of generators $X$ is modified. Any non-free finitely generated Lie algebra can be written as $L(X)/I$ with an ideal $I$ encoding the relations. Intended for cases where $I$ is not explicitly known, a variant of the algorithm iteratively lists a basis of $L(X)/I$ and a self-reduced basis of $I$. Further modifications that take advantage of restrictions enforced by a gradation on $L(X)/I$ are also given.2021-06-2