Physical Review A
Asymptotically close to the Nth-order multicritical point of an N-phase system, there are N-1 sum rules involving the mean-field susceptibilities measured in each of the coexisting phases. These sum rules provide the experimentalist a convenient and stringent test of the theory. In particular, they facilitate the detection of nonclassical effects, especially valuable for N>3 where the fluctuation effect is dominated by the classical contribution for three-dimensional systems.
Kaufman, Miron and Ma, Michael, "Multicritical Susceptibility Sum Rules" (1987). Physics Faculty Publications. 135.
Kaufman, Miron and Michael Ma. "Multicritical Susceptibility Sum Rules." Physical Review A 35 (1987): 2369-2372.
Copyright 1987 American Physical Society. Available on publisher's site at http://pra.aps.org/abstract/PRA/v35/i5/p2369_1.