General-term conjecture for the short-time expansion of the KPZ generating function

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Let gg be the function used to define Qt,β(σ)Q_{t,\beta}(\sigma), let Li\mathfrak{L}_i denote the corresponding coefficients, and let n=(n1,…,nr+2−2q)\mathbf{n}=(n_1,\ldots,n_{r+2-2q}). If the distinct values among the njn_j have multiplicities m1,…,mkm_1,\ldots,m_k, define the symmetry factor S(n)=m1!⋯mk!S(\mathbf{n})=m_1!\cdots m_k!. For σ<1\sigma<1, the general-term conjecture. The short-time expansion of log⁡Qt,β(σ)\log Q_{t,\beta}(\sigma) has the form

log⁡Qt,β(σ)=1πt∫0+∞dxx g(σe−x)+14π2∫0σdu u[∂u∫−∞+∞dp g(ue−p2)]2+∑r=1+∞∑q=0r2+12r+1−3q(2q+1)!tr/2∑r+2≥n1≥…≥nr+2−2q≥0 1+…+nr+2−2q=r−1+qcr,q(n)S(n)∏j=1r+2−2qLnj+1nj!.\begin{aligned} \log Q_{t,\beta}(\sigma)={}&\frac{1}{\pi \sqrt{t}}\int_{0}^{+\infty}\mathrm{d}x\sqrt{x}\,g(\sigma e^{-x})+\frac{1}{4\pi^2}\int_0^\sigma\mathrm{d}u\,u\left[\partial_u\int_{-\infty}^{+\infty}\mathrm{d}p\,g(u e^{-p^2})\right]^2\\\\ &+\sum_{r=1}^{+\infty}\sum_{q=0}^{\frac{r}{2}+1}\frac{2^{r+1-3q}}{(2q+1)!}t^{r/2}\sum_{\substack{r+2\geq n_1\geq\ldots\geq n_{r+2-2q}\geq0\\\ _1+\ldots+n_{r+2-2q}=r-1+q}}\frac{c_{r,q}(\mathbf{n})}{S(\mathbf{n})}\prod_{j=1}^{r+2-2q}\frac{\mathfrak{L}_{n_j+1}}{n_j!}. \end{aligned}

Here the coefficients cr,q(n)c_{r,q}(\mathbf{n}) are positive integers. The conjecture is motivated by the explicitly computed expansion through order t3t^3, but precise analytical expressions for arbitrary high orders were not obtained, so the general form remains open.

References

Primary source

Alexandre Krajenbrink, Pierre Le Doussal and Sylvain Prolhac, “Systematic time expansion for the Kardar-Parisi-Zhang equation, linear statistics of the GUE at the edge and trapped fermions”, arXiv:1808.07710 (2018).

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