COMPLETE NONDIAGONAL REFLECTION MATRICES OF RSOS SOS AND HARD HEXAGONMODELS/

In this paper we compute the most general non-diagonal reflection matr ices of the RSOS/SOS models and the hard hexagon model using the bound ary Yang-Baxter equations. We find a new one-parameter family of the r eflection matrices for the RSOS model in addition to the previous resu lt obtained in (Ahn C and Koo W M 1996 Nucl. Phys. B 468 [FS] 461). We also End three classes of the reflection matrices for the SOS model, which has one or two free parameters. For the hard-hexagon model which can be mapped to the RSOS(5) model by folding four RSOS heights into two, the solutions can be obtained similarly with a main difference in the boundary unitarity conditions. Due to this, the reflection matric es dan have two free parameters. We show that these extra terms can be identified with the 'decorated' solutions. We also generalize the har d hexagon model by 'folding' the RSOS heights of the general RSOS(p) m odel and show that they satisfy the integrability conditions such as t he Yang-Baxter and boundary Yang-Baxter equations. These models can be solved using the results for the RSOS models.