Fri April 10 2015, 1:00 PM in Aula Bianchi, Scuola Normale Superiore Pisa Joao da Gama Batista Laboratoire de mathématiques appliquées aux systèmes École Centrale de Paris will deliver the seminar "Sudden trust collapse in networked societies" Abstract: Trust is a collective, self-fulfilling phenomenon that suggests analogies with phase transitions. We introduce a stylized model for the build-up and collapse of trust in networks, which generically displays a first order transition. The basic assumption of our model is that whereas trustworthiness begets trustworthiness, panic also begets panic, in the sense that a small decrease in trustworthiness may be amplified and ultimately lead to a sudden and catastrophic drop of collective trust. We show, using both numerical simulations and mean-field analytic arguments, that there are extended regions of the parameter space where two equilibrium states coexist: a well-connected network where global confidence is high, and a poorly connected network where global confidence is low. In these coexistence regions, spontaneous jumps from the well-connected state to the poorly connected state can occur, corresponding to a sudden collapse of trust that is not caused by any major external catastrophe. In large systems, spontaneous crises are replaced by history dependence: whether the system is found in one state or in the other essentially depends on initial conditions. All interested people are kindly invited. Best, Giacomo -- Giacomo Bormetti Assistant Professor of Financial Mathematics -------------------------- Faculty of Sciences Scuola Normale Superiore Pisa Piazza dei Cavalieri, 7 56126 Pisa - Italy email: giacomo.bormetti@sns.it http://mathfinance.sns.it/index.php/people/41-group-members/51-giacomo-borme... phone: +39 050 509248