<p>In long-range percolation on <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathbb {Z}^d\)</EquationSource> </InlineEquation>, we connect each pair of distinct points <i>x</i> and <i>y</i> by an edge independently at random with probability <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(1-\exp (-\beta \Vert x-y\Vert ^{-d-\alpha })\)</EquationSource> </InlineEquation>, where <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\alpha &gt;0\)</EquationSource> </InlineEquation> is fixed and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\beta \ge 0\)</EquationSource> </InlineEquation> is a parameter. In a previous paper, we proved that if <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(0&lt;\alpha &lt;d\)</EquationSource> </InlineEquation> then the critical two-point function satisfies the <i>spatially averaged</i> upper bound <Equation ID="Equ12"> <EquationSource Format="TEX">\(\frac{1}{r^d}\sum _{x\in [-r,r]^d} \mathbb {P}_{\beta _c}(0\leftrightarrow x) \preceq r^{-d+\alpha }\)</EquationSource> </Equation>for every <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(r\ge 1\)</EquationSource> </InlineEquation>. This upper bound is believed to be sharp for values of <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\alpha\)</EquationSource> </InlineEquation> strictly below the <i>crossover value</i> <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\alpha _c(d)\)</EquationSource> </InlineEquation>, and a matching lower bound for <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\alpha &lt;1\)</EquationSource> </InlineEquation> was proven by Bäumler and Berger (AIHP 2022). In this paper, we prove <i>pointwise</i> upper and lower bounds of the same order under the same assumption that <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\alpha &lt;1\)</EquationSource> </InlineEquation>. We also prove analogous two-sided pointwise estimates on the <i>slightly subcritical</i> two-point function under the same hypotheses, interpolating between <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\Vert x \Vert ^{-d+\alpha }\)</EquationSource> </InlineEquation> decay below the correlation length and <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\Vert x \Vert ^{-d-\alpha }\)</EquationSource> </InlineEquation> decay above the correlation length. In dimensions <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(d=1,2,3\)</EquationSource> </InlineEquation>, we deduce that the triangle condition holds under the minimal assumption that <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(0&lt;\alpha &lt;d/3\)</EquationSource> </InlineEquation>. While this result had previously been established under additional perturbative assumptions using the lace expansion, our proof is completely non-perturbative and does not rely on the lace expansion in any way.</p>

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Pointwise two-point function estimates and a non-perturbative proof of mean-field critical behaviour for long-range percolation

  • Tom Hutchcroft

摘要

In long-range percolation on \(\mathbb {Z}^d\) , we connect each pair of distinct points x and y by an edge independently at random with probability \(1-\exp (-\beta \Vert x-y\Vert ^{-d-\alpha })\) , where \(\alpha >0\) is fixed and \(\beta \ge 0\) is a parameter. In a previous paper, we proved that if \(0<\alpha <d\) then the critical two-point function satisfies the spatially averaged upper bound \(\frac{1}{r^d}\sum _{x\in [-r,r]^d} \mathbb {P}_{\beta _c}(0\leftrightarrow x) \preceq r^{-d+\alpha }\) for every \(r\ge 1\) . This upper bound is believed to be sharp for values of \(\alpha\) strictly below the crossover value \(\alpha _c(d)\) , and a matching lower bound for \(\alpha <1\) was proven by Bäumler and Berger (AIHP 2022). In this paper, we prove pointwise upper and lower bounds of the same order under the same assumption that \(\alpha <1\) . We also prove analogous two-sided pointwise estimates on the slightly subcritical two-point function under the same hypotheses, interpolating between \(\Vert x \Vert ^{-d+\alpha }\) decay below the correlation length and \(\Vert x \Vert ^{-d-\alpha }\) decay above the correlation length. In dimensions \(d=1,2,3\) , we deduce that the triangle condition holds under the minimal assumption that \(0<\alpha <d/3\) . While this result had previously been established under additional perturbative assumptions using the lace expansion, our proof is completely non-perturbative and does not rely on the lace expansion in any way.