CORRELATION TRANSITIONS IN THE ISING CHAIN WITH COMPETING SHORT-RANGEAND LONG-RANGE MIRROR INTERACTIONS

We present exact four-spin- and string-correlation functions derived f or an Ising chain with competing geometrical nearest-neighbor short-ra nge and mirror-image-type long-range interactions. Unusual T not equal 0 correlation effects were found, indicating qualitative changes in t he behavior of the system in different T domains. These domains are no t separated by a sharp, traditional phase transition, but are delimite d by a temperature T-i at which the exact connected four-spin-correlat ion function vanishes. At the same T-i the pair-correlation function c hanges its character: The functional form of the correlation length an d the nature of the long-range decay are modified. [S1063-651X(98)0961 0-X].