Boundary extremal-process conjecture between CI\mathcal{C}_I and CIII\mathcal{C}_{III}

Let β>1\beta>1 and σ2=β2β1\sigma^2=\frac{\beta}{2\beta-1}, and let Nt2\mathcal{N}_t^2 be the set of type-22 particles at time tt, with positions Xu(t)X_u(t). Write Z(1)Z^{(1)}_\infty for the type-11 derivative martingale limit, and let DPPP(μ,D)\operatorname{DPPP}(\mu,\mathfrak{D}) denote a decorated Poisson point process with intensity measure μ\mu and decoration point measure D\mathfrak{D}. Boundary extremal-process conjecture. There exist c>0c>0 and a random decoration point measure D~\widetilde{\mathfrak{D}} such that

uNt2δXu(t)2βσ2t+12β/σ2logt\sum_{u \in \mathcal{N}_t^2} \delta_{X_u(t) - \sqrt{2\beta\sigma^2}t + \frac{1}{\sqrt{2\beta/\sigma^2}} \log t}

converges in distribution to

DPPP(cZ(1)e2β/σ2xdx,D~).\operatorname{DPPP}\left(c Z^{(1)}_\infty e^{-\sqrt{2\beta/\sigma^2}x}\,\mathrm{d}x,\widetilde{\mathfrak{D}}\right).

Particles of type 22 contributing to the extremal process are expected to satisfy tT(u)=O(t1/2)t-T(u)=O(t^{1/2}), so the intensity should be driven by the type-11 derivative martingale, while the decoration should be the extremal process of a type-22 BBM conditioned to travel at speed 2βσ2>2\sqrt{2\beta\sigma^2}>\sqrt{2}. The conjecture concerns the boundary between the two established parameter regions and remains open.

Sources & referencesView supporting material

Primary source

Mohamed Ali Belloum and Bastien Mallein, “Anomalous spreading in reducible multitype branching Brownian motion”, arXiv:2011.03223 (2021).

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