title: Ruling out static latent homophily in citation networks.
abstract: Citation and coauthor networks offer an insight into the dynamics of scientific progress. We can also view them as representations of a causal structure, a logical process captured in a graph. From a causal perspective, we can ask questions such as whether authors form groups primarily due to their prior shared interest, or if their favourite topics are 'contagious' and spread through co-authorship. Such networks have been widely studied by the artificial intelligence community, and recently a connection has been made to nonlocal correlations produced by entangled particles in quantum physics-the impact of latent hidden variables can be analyzed by the same algebraic geometric methodology that relies on a sequence of semidefinite programming (SDP) relaxations. Following this trail, we treat our sample coauthor network as a causal graph and, using SDP relaxations, rule out latent homophily as a manifestation of prior shared interest only, leading to the observed patternedness. By introducing algebraic geometry to citation studies, we add a new tool to existing methods for the analysis of content-related social influences.
authors.affiliation: ICFO-The Institute of Photonic Sciences, Barcelona Institute of Science and Technology, Av. Carl Friedrich Gauss, 3, 08860 Castelldefels, Spain.|University of Borås, Allegatan 1, 50190 Borås, Sweden.
authors.forename: Peter
authors.identifier: 0000-0002-1539-8256
authors.initials: P
authors.lastname: Wittek
authors.affiliation: University of Borås, Allegatan 1, 50190 Borås, Sweden.
authors.forename: Sándor
authors.initials: S
authors.lastname: Darányi
authors.affiliation: University of Borås, Allegatan 1, 50190 Borås, Sweden.
authors.forename: Gustaf
authors.initials: G
authors.lastname: Nelhans
keywords: Causal network; Citation network; Hidden variables; Semidefinite programming; Sum-of-squares decomposition