Essays on Networks: Theory and Applications

Networks have proven to be a useful representation of various systems. Social and economic interactions, biological and ecological systems, the internet can be understood better if modelled as networks. Intuitively, a network describes a collection of nodes and the links between them. The notion of nodes is fairly general, they may be individuals or firms or countries. A link between two nodes represents a direct relation between them; for instance, a link could be a friendship tie between people, a research and development agreement between firms, or, in the context of countries, a link may be a mutual defense pact. The study of networks spans across disciplines. A central field in sociology and studied in depth by mathematicians over the past fifty years, networks have recently received extensive attention in statistical physics, computer science, business strategy and organization theory. While economists have occasionally showed interest in networks, a literature has emerged only in the last decade. This thesis brings two contributions. On the one hand, it aims to enhance the role of network theories in solving economic issues, by proposing a network representation of financial systems. On the other hand, it aims to enrich the set of methods used to analyze networks, by introducing economic microfoundations to a preferential attachment model of network formation.

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