  In this study, we consider generalized probabilistic theories (GPTs) and
focus on a class of theories called regular polygon theories, which can be
regarded as natural generalizations of a two-level quantum system (a qubit
system). In the usual CHSH setting for quantum theory, the CHSH value is known
to be optimized by maximally entangled states. This research will reveal that
the same observations are obtained also in regular polygon theories. Our result
gives a physical meaning to the concept of ``maximal entanglement" in regular
polygon theories.
