Another phase transition in the Axelrod model

Axelrod's model of cultural dissemination, despite its apparent simplicity, demonstrates complex behavior that has been of much interest in statistical physics. Despite the many variations and extensions of the model that have been investigated, a systematic investigation of the effects of changing the size of the neighborhood on the lattice in which interactions can occur has not been made. Here we investigate the effect of varying the radius R of the von Neumann neighborhood in which agents can interact. We show, in addition to the well-known phase transition at the critical value of q, the number of traits, another phase transition at a critical value of R, and draw a q - R phase diagram for the Axelrod model on a square lattice. In addition, we present a mean-field approximation of the model in which behavior on an infinite lattice can be analyzed

European integration and the social science of EU studies: the disciplinary politics of a subfield

This article takes the 50th anniversary of the Treaty of Rome as an opportunity to reflect upon half a century of academic discourse about the EU and its antecedents. In particular, it illuminates the theoretical analysis of European integration that has developed within political science and international studies broadly defined. It asks whether it is appropriate to map, as might be tempting, the intellectual 'progress' of the field of study against the empirical evolution of its object (European integration/the EU). The argument to be presented here is that while we can, to some extent, comprehend the evolution of academic thinking about the EU as a reflex to critical shifts in the 'real world' of European integration ('externalist' drivers), it is also necessary to understand 'internalist' drivers of theoretical discourse on European integration/the EU. The article contemplates two such 'internalist' components that have shaped and continue to shape the course of EU studies: scholarly contingency (the fact that scholarship does not proceed with free agency, but is bound by various conditions) and disciplinary politics (the idea that the course of academic work is governed by power games and that there are likely significant disagreements about best practice and progress in a field). In terms of EU studies, the thrust of disciplinary politics tends towards an opposition between 'mainstreaming' and 'pluralist versions' of the political science of EU studies. The final section explores how, in the face of emerging monistic claims about propriety in the field, an effective pluralist political science of the EU might be enhanced

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements