Transition from coherence to bistability in a model of financial markets

We present a model describing the competition between information transmission and decisionmaking in financial markets. The solution of this simple model is recalled, and possible variations discussed.It is shown numerically that despite its simplicity, it can mimic a size effect comparable to a crash. Twoextensions of this model are presented that allow to simulate the demand process. One of these extensionshas a coherent stable equilibrium and is self-organized, while the other has a bistable equilibrium, with aspontaneous segregation of the population of agents. A new model is introduced to generate a transitionbetween those two equilibriums. We show that the coherent state is dominant up to an equal mixing of thetwo extensions. We focuss our attention on the microscopic structure of the investment rate, which is themain parameter of the original model. A constant investment rate seems to be a very good approximation.