EXACT PARTITION AND PAIR-CORRELATION FUNCTIONS FOR AN ISING-MODEL WITH MIRROR-IMAGE-TYPE INTERACTIONS

The exact partition function, free energy, pair-correlation function, and connected quantities like entropy, specific heat, and magnetic sus ceptibility were deduced for an Ising chain in which each spin interac ts with its mirror-image spin and the neighbors of the image. A qualit atively different behavior was found for the pair-correlation function in low- and high-temperature limits, which was interpreted in terms o f bound spin pairs emerging in the low-T regime. The physical implicat ions of the model are analyzed, and applications in condensed matter a nd biology discussed.