A model for social dynamics with controlled mass media.

We study the effect of mass media, modeled as an applied external
field, on a social system based on Axelrod\'s model for the dissemination of
culture. The numerical simulations show that the system undergoes a
nonequilibrium phase transition between an ordered phase (homogeneous culture)
specified by the mass media and a disordered (culturally fragmented) one.
The critical boundary separating these phases is calculated on the parameter space
of the system, given by the intensity of the mass media influence and the number of
options per cultural attribute. Counterintuitively, mass media can induce cultural
diversity when its intensity is above some threshold value. The nature of the phase
transition changes from continuous to discontinuous at some critical value of the number
of options