Fractional Gaussian Forms and Gauge Theory: An Overview
Sky Cao , Scott Sheffield
Frontiers of Mathematics ›› 2026, Vol. 21 ›› Issue (1) : 1 -137.
Fractional Gaussian Forms and Gauge Theory: An Overview
Fractional Gaussian fields are scalar-valued random functions or generalized functions on an n-dimensional manifold M, indexed by a parameter s. They include white noise (s = 0), Brownian motion (s = 1, n = 1), the 2D Gaussian free field (s = 1, n = 2) and the membrane model (s = 2). These simple objects are ubiquitous in math and science, and can be used as a starting point for constructing non-Gaussian theories. They are sometimes parameterized by the Hurst parameter
The differential form analogs of these objects are equally natural: for example, instead of considering an instance h(x) of the GFF on ℝ2, one might write h1(x)dx1 + h2(x)dx2 where h1 and h2 are independent GFF instances. This “Gaussian-free-field-based 1-form” can be projected onto curl-free and divergence-free components, which in turn arise as gradients and dual-gradients of independent membrane models.
In general, given k ∈ {0,1,…, n}, an instance of the fractional Gaussian k-form with parameter s ∈ ℝ (abbreviated FGFsk(M)) is given by
The 1-form FGF11(M) and its gauge-fixed projection FGF11(M)d*=0 arise as low-temperature/small-scale limits of U(1) Yang–Mills gauge theory. When U(1) is replaced with another compact Lie group, the corresponding limit is a Lie-algebra-valued analog of FGF11(M)d*=0, which can be interpreted as a random connection whose curvature is (a Lie-algebra valued analog of) FGF20(M)d=0.
Wilson loop observables of this connection are defined for sufficiently regular “big loops” (trajectories in the space of divergence-free 1-forms obtainable as limits of finite-length loops) in a gauge invariant way, even in the non-abelian case. We define “big surfaces” (trajectories in the space of 2-forms obtainable as limits of smooth surfaces with boundary) and note that Stokes’ theorem converts big-loop integrals of FGF11(M)d*=0 into big-surface integrals of FGF20(M)d=0 or FGF20(M). A type of exponential correlation decay and area law applies within the slabs ℝ2 × [0,1]m but not within ℝn for n > 2.
One may interpret FGF11(M)d*=0 as a random divergence-free vector field, which is conjectured to be the fine-mesh scaling limit of the n-dimensional dimer model when n > 2. (Kenyon proved this for n = 2.) We formulate several conjectures and open problems about scaling limits, including possible off-critical/non-Gaussian limits, whose construction in the Yang–Mills setting is a famous open problem.
Gaussian k-forms / random distributions / Yang–Mills / 60G60 / 81T13
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Peking University
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