Order-disorder displacive crossover in a structural phase transition model

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Abstract
The authors write the partition function of the double-Gaussian model, which is representative of the lambda phi 4 class (Hamiltonians with unbounded doubly degenerate local potentials), exactly as the product of the partition function of a Gaussian model and the partition function of a spin-1/2 Ising model. On the basis of this result they are able to determine the nature and location of the critical points of this model. It also follows that the block spin renormalisation group flows in the entire high-temperature region converge to a Gaussian model fixed point.