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

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Let β>1\beta>1 and σ2=β2β−1\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

∑u∈Nt2δXu(t)−2βσ2t+12β/σ2log⁡t\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)e−2β/σ2x dx,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 t−T(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.

References

Primary source

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

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