Critical behavior of three interacting strings

The unbinding of three strings in a plane which interact via short-ranged attractive potentials is studied using both transfer-matrix methods and Monte Carlo techniques. In the symmetric case, for which the two outer strings have the same line tension, the critical behavior depends on the relative flexibility of the inner string in a nonuniversal fashion. In the asymmetric case, the strings unbind in two successsive unbinding transitions at two different temperatures. Renormalization-group arguments predict that these results are also applicable to the adhesion and unbinding of three membranes.