Abstract
The partition function of the directed polymer model on \({\mathbb {Z}}^{2+1}\) undergoes a phase transition in a suitable continuum and weak disorder limit. In this paper, we focus on a window around the critical point. Exploiting local renewal theorems, we compute the limiting third moment of the space-averaged partition function, showing that it is uniformly bounded. This implies that the rescaled partition functions, viewed as a generalized random field on \({\mathbb {R}}^{2}\), have non-trivial subsequential limits, and each such limit has the same explicit covariance structure. We obtain analogous results for the stochastic heat equation on \({\mathbb {R}}^2\), extending previous work by Bertini and Cancrini (J Phys A Math Gen 31:615, 1998).
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Notes
Note that coordinates \((n^\alpha _i,x^\alpha _i)\) with the same label \(\alpha \in \{a,b,c\}\) are distinct, by \(n^\alpha _i < n^\alpha _{i+1}\), see (1.39), hence more than triple matchings cannot occur.
\(S^{(N)}\) should not be confused with the random walk S in the definition of the directed polymer model.
The precise constant \(4 \pi \) in (8.2) is the one relevant for us, but any other positive constant would do.
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Acknowledgements
F.C. is supported by the PRIN Grant 20155PAWZB “Large Scale Random Structures”. R.S. is supported by NUS Grant R-146-000-253-114. N.Z. is supported by EPRSC through Grant EP/R024456/1.
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Caravenna, F., Sun, R. & Zygouras, N. On the Moments of the \((2+1)\)-Dimensional Directed Polymer and Stochastic Heat Equation in the Critical Window. Commun. Math. Phys. 372, 385–440 (2019). https://doi.org/10.1007/s00220-019-03527-z
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DOI: https://doi.org/10.1007/s00220-019-03527-z