Two standard invariants used to study the fundamental group of the complement X of a hyperplane arrangement are the Malcev completion of its fundamental group G and the cohomology groups of X with coefficients in rank one local systems. In this thesis, we develop a tool that unifies these two approaches. This tool is the Malcev completion S_p of G relative to a homomorphism p from G into (C^*)^N. The relative completion S_p is a prosolvable group that generalizes the classical Malcev completion; when p is the trivial representation, S_p is the Malcev completion of G. The group S_p is tightly controlled by the cohomology groups H^1(X,L_{p^k}) with coefficients in the irreducible local systems L_{p^k} associated to the representation p.The pronilpotent Lie algebra u_p of the prounipotent radical U_p of S_p has been described by Hain. If p is the trivial representation, then u_p is the holonomy Lie algebra, which is well-known to be quadratically presented. In contrast, we show that when X is the complement of the braid arrangement in complex two-space, there are infinitely many representations p from G into (C^*)^2 for which u_p is not quadratically presented.We show that if Y is a subtorus of the character torus T containing the trivial character, then S_p is combinatorially determined for general p in Y. We do not know whether S_p is always combinatorially determined. If S_p is combinatorially determined for all characters p of G, then the characteristic varieties of the arrangement X are combinatorially determined.When Y is an irreducible subvariety of T^N, we examine the behavior of S_p as p varies in Y. We define an affine group scheme S_Y over Y such that if Y = {p}, then S_Y is the relative Malcev completion S_p. For each p in Y, there is a canonical homomorphism of affine group schemes from S_p into the affine group scheme which is the restriction of S_Y to p. This is often an isomorphism. For example, if there exists p in Y whose image is Zariski dense in G_m^N, then this homomorphism is an isomorphism for general p in Y. / Dissertation

In den vergangenen Jahrzehnten rückte das häufige Auftreten von multiplen Polylogarithmen und multiplen Zeta-Werten, in Feynman-Diagramm Rechnungen niedriger Ordnung, verstärkt in den wissenschaftlichen Fokus. Hierbei offenbarte sich eine Verbindung zu den mathematischen Theorien der Perioden und der iterierten Integrale von Chen. Eine ähnliche Allgegenwärtigkeit von multiplen Zeta-Werten wurde jüngst auch in der α'-Entwicklung von Genus-Null Stringtheorie Amplituden beobachtet. Davon inspiriert befasst sich diese Arbeit mit der Systematik der iterierten Integralen in den Streuamplituden der offenen Stringtheorie. Unser Fokus liegt insbesondere auf der Genus-Eins Amplitude, welche sich vollständig durch iterierte Integrale, die bezüglich einer punktierten elliptischen Kurve definiert sind, ausdrücken lässt. Wir führen den Begriff der getwisteten elliptischen multiplen Zeta-Werte ein. Dieser Begriff beschreibt eine Klasse von iterierten Integralen, die auf einer elliptischen Kurve definiert sind, bei welcher ein rationales Gitter entfernt wurde. Anschließend zeigen wir, dass die Entwicklung eines jeden getwisteten elliptischen multiplen Zeta-Wertes, bezüglich des modularen Parameters τ, durch ein Anfangswertproblem beschrieben wird. Weiterhin präsentieren wir ein Argument dafür, dass sich im Limes τ→i∞ jeder getwistete elliptische multiple Zeta-Wert durch zyklotomische multiple Zeta-Werte ausdrücken lässt. Schließlich beschreiben wir wie sich Genus-Eins Amplituden in offener Stringtheorie mithilfe von getwisteten elliptischen multiplen Zeta-Werten ausdrücken lassen und illustrieren dies für die Vier-Punkt Amplitude. Hierbei zeigt es sich, dass bis zu dritter Ordnung in α' alle Beiträge durch die Unterklasse der elliptischen multiplen Zeta-Werte ausgedrückt werden können, was wiederum äquivalent zu der Abwesenheit unphysikalischer Pole in Gliozzi-Scherk-Olive projizierter Superstringtheorie ist. / Over the last few decades the prevalence of multiple polylogarithms and multiple zeta values in low order Feynman diagram computations of quantum field theory has received increased attention, revealing a link to the mathematical theories of Chen’s iterated integrals and periods. More recently, a similar ubiquity of multiple zeta values was observed in the α'-expansion of genus-zero string theory amplitudes. Inspired by these developments, this work is concerned with the systematic appearance of iterated integrals in scattering amplitudes of open superstring theory. In particular, the focus will be on studying the genus-one amplitude, which requires the notion of iterated integrals defined on punctured elliptic curves. We introduce the notion of twisted elliptic multiple zeta values that are defined as a class of iterated integrals naturally associated to an elliptic curve with a rational lattice removed. Subsequently, we establish an initial value problem that determines the expansions of twisted elliptic multiple zeta values in terms of the modular parameter τ of the elliptic curve. Any twisted elliptic multiple zeta value degenerates to cyclotomic multiple zeta values at the cusp τ → i∞, with the corresponding limit serving as the initial condition of the initial value problem. Finally, we describe how to express genus-one open-string amplitudes in terms of twisted elliptic multiple zeta values and study the four-point genus-one open-string amplitude as an example. For this example we find that up to third order in α' all possible contributions in fact belong to the subclass formed by elliptic multiple zeta values, which is equivalent to the absence of unphysical poles in Gliozzi-Scherk-Olive projected superstring theory.

Soit K|Q un corps de nombres et soit ζK(s) sa fonction L complexe associée. La formule analytique du nombre de classes fournit un lien entre les valeurs spéciales de ζK(s) et les invariants du corps K. Elle admet une version Galois-équivariante. On a un schema similaire pour les courbes elliptiques. Soit E/Q une courbe elliptique et soit L(E/Q, s) sa fonction L complexe associée. La conjecture de Birch et Swinnerton-Dyer prédit un lien entre le comportement de L(E/Q, s) au point s = 1 et la structure des solutions rationnelles de l’équation definie par E. Comme la formule analytique du nombre de classes, la conjecture de Birch et Swinnerton-Dyer admet une version équivariante. La conjecture de Stark elliptique formulée par H. Darmon, A. Lauder et V. Rotger propose un analogue p-adique de la conjecture de Birch et Swinnerton-Dyer équivariante, qui nécessite certaines hypothèses. Dans leur article, les auteurs formulent la conjecture et donnent une démonstration dans certains cas où E a bonne réduction en p. Pour cela, ils utilisent la méthode de Garrett-Hida qui conduit à une factorisation de fonctions L p-adiques. Dans cette thèse on se concentre sur la conjecture de Stark elliptique et l’on montre comme il est possible d’étendre le résultat de Darmon, Lauder et Rotger. Dans le cas où E a bonne réduction en p on peut étendre le résultat en utilisant la méthode de Hida- Rankin. Cette méthode nous donne un contrôle meilleur sur les constantes apparaissant dans les formules et nous amène à une formule explicite contenant les invariants de la courbe elliptique. Pour obtenir le résultat on adapte la preuve du théorème principal de Darmon, Lauder et Rotger à notre cas et on utilise une formule p-adique de Gross et Zagier qui relie les valeurs spéciales de la fonction L padique de Bertolini-Darmon-Prasanna et les points de Heegner. Ensuite on voit comment étendre notre résultat et celui de Darmon-Lauder-Rotger au cas où E a réduction multiplicative en p. Dans ce cadre, on ne peut pas utiliser la fonction L p-adique de Bertolini-Darmon-Prasanna en raison de problèmes techniques. Pour éliminer cette difficulté on consid`ere la fonction L p-adique de Castellà. On utilise aussi la méthode de Garrett-Hida ainsi que la méthode d’Hida-Rankin et l’on obtient des résultats similaires aux cas de bonne réduction. / Let K|Q be a number field and let ζK(s) be its associated complex L-function. The analytic class number formula relates special values of ζK(s) with algebraic invariants of the field K itself. It admits a Galois equivariant refinement known as Stark conjectures. We have a very similar picture in the case of elliptic curves. Let E/Q be an elliptic curve and let L(E/Q, s) be its associated complex L-function. The conjecture of Birch and Swinnerton-Dyer relates the behaviour of L(E/Q, s) at s = 1 to the structure of rational solutions of the equation defined by E. The equivariant Birch and Swinnerton- Dyer conjecture is obtained including in the picture the action of Galois groups. The elliptic Stark conjecture formulated by H. Darmon, A. Lauder and V. Rotger purposes a p-adic analogue of the equivariant Birch and Swinnerton-Dyer conjecture, under several assumption. In their paper, the authors formulate the conjecture and prove it in some cases of good reduction of E at p using Garrett-Hida method and performing a factorization of p-adic L-functions. In this dissertation we focus on the elliptic Stark conjecture and we show how it is possible to extend the result of Darmon, Lauder and Rotger. In the case of good reduction of E at p we can slightly extend the result using Hida- Rankin method. This method also gives us a better control of the constants appearing in the result, thus yielding an explicit formula which contains invariants associated with the elliptic curve. To achieve the proof we mimic the main result of Darmon, Lauder and Rotger in our setting and we make use of a p-adic Gross-Zagier formula which relates special values of the Bertolini-Darmon-Prasanna p-adic L-function to Heegner points. In a second moment we extend both our result and Darmon-Lauder-Rotger result to the case of multi- plicative reduction of E at p. In this setting we cannot use Bertolini- Darmon Prasanna p-adic L-function due to some technical reasons. In order to avoid the problem we consider Castellà’s two variables p-adic L-function. We use both Garrett-Hida method and Hida-Rankin method. In the two cases we obtain formulae which are similar to those of the good reduction setting.