Abstract
We prove that the scaling limits of spin fluctuations in four-dimensional
Ising-type models with nearest-neighbor ferromagnetic interaction at or near
the critical point are Gaussian. A similar statement is proven for the $łambda
\phi^4$ fields over $R^4$ with a lattice ultraviolet cutoff, in the
limit of infinite volume and vanishing lattice spacing. The proofs are enabled
by the models' random current representation, in which the correlation
functions' deviation from Wick's law is expressed in terms of intersection
probabilities of random currents with sources at distances which are large on
the model's lattice scale. Guided by the analogy with random walk intersection
amplitudes, the analysis focuses on the improvement of the so-called tree
diagram bound by a logarithmic correction term, which is derived here through
multi-scale analysis.
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