3 INTERACTING STRINGS IN 2 DIMENSIONS - NONUNIVERSAL AND MULTIPLE UNBINDING TRANSITIONS

Three non-intersecting strings in two dimensions which interact via sh ort-ranged attractive potentials are studied using both transfer matri x methods and Monte Carlo techniques. The critical behavior at the unb inding transition and the critical values of the potential strength ar e determined for symmetric and asymmetric bundles of strings. In the a symmetric case, for which the two outer strings have different line te nsions (or interact via different potentials), the strings unbind in t wo subsequent transitions, which then exhibit universal critical behav ior. In the symmetric case, where the two outer strings have the same line tension, the three strings unbind simultaneously. The critical be havior at this unbinding transition is found to be non-universal for t he whole range of accessible length scales, but its parameter dependen ce is found to be in strong disagreement with the predictions of the s o-called necklace model. The more flexible the inner string, the deepe r the critical potential. However, within the numerical error, three i dentical strings are found to unbind at the same critical potential st rength as two strings with the same line tensions.