  In studies of social dynamics, cohesion refers to a group's tendency to stay
in unity, which -- as argued in sociometry -- arises from the network topology
of interpersonal ties between members of the group. We follow this idea and
propose a game-based model of cohesion that not only relies on the social
network, but also reflects individuals' social needs. In particular, our model
is a type of cooperative games where players may gain popularity by
strategically forming groups. A group is socially cohesive if the grand
coalition is core stable. We study social cohesion in some special types of
graphs and draw a link between social cohesion and the classical notion of
structural cohesion. We then focus on the problem of deciding whether a given
social network is socially cohesive and show that this problem is
CoNP-complete. Nevertheless, we give two efficient heuristics for coalition
structures where players enjoy high popularity and experimentally evaluate
their performances.
