  We present a generalization of the dynamical model of information
transmission and herd behavior proposed by Eguiluz and Zimmermann. A
characteristic size of group of agents $s_{0}$ is introduced. The fragmentation
and coagulation rates of groups of agents are assumed to depend on the size of
the group. We present results of numerical simulations and mean field analysis.
It is found that the size distribution of groups of agents $n_{s}$ exhibits two
distinct scaling behavior depending on $s \leq s_{0}$ or $s > s_{0}$. For $s
\leq s_{0}$, $n_{s} \sim s^{-(5/2 + \delta)}$, while for $s > s_{0}$, $n_{s}
\sim s^{-(5/2 -\delta)}$, where $\delta$ is a model parameter representing the
sensitivity of the fragmentation and coagulation rates to the size of the
group. Our model thus gives a tunable exponent for the size distribution
together with two scaling regimes separated by a characteristic size $s_{0}$.
Suitably interpreted, our model can be used to represent the formation of
groups of customers for certain products produced by manufacturers. This, in
turn, leads to a distribution in the size of businesses. The characteristic
size $s_{0}$, in this context, represents the size of a business for which the
customer group becomes too large to be kept happy but too small for the
business to become a brand name.
