Upper deviation probabilities for the range of a supercritical super-Brownian motion

TL;DR

This paper confirms a conjecture about the exponential decay rate of the probability that the range of a supercritical super-Brownian motion exceeds a linear threshold, extending understanding of its upper deviation behavior.

Contribution

The paper proves the conjectured asymptotic decay rate for the upper deviation probabilities of the range radius in supercritical super-Brownian motion.

Findings

Confirmed the conjecture on upper deviation probabilities.

Derived the exponential decay rate for large deviations.

Extended theoretical understanding of super-Brownian motion range behavior.

Abstract

Let $\{X_t\}_{t\geq 0 }$ be a $d$-dimensional supercritical super-Brownian motion started from the origin with branching mechanism $\psi$. Denote by $R_t:=\inf\{r>0:X_s(\{x\in \mathbb{R}^d:|x|\geq r\})=0,~\forall~0\leq s\leq t\}$ the radius of the minimal ball (centered at the origin) containing the range of $\{X_s\}_{s\geq 0 }$ up to time $t$. In \cite{Pinsky}, Pinsky proved that condition on non-extinction, $\lim_{t\to\infty}R_t/t=\sqrt{2\beta}$ in probability, where $\beta:=-\psi'(0)$. Afterwards, Engl\"{a}nder \cite{Englander04} studied the lower deviation probabilities of $R_t$. For the upper deviation probabilities, he \cite[Conjecture 8]{Englander04} conjectured that for $\rho>\sqrt {2\beta}$, $$ \lim_{t\to\infty}\frac{1}{t}\log\mathbb{P}(R_t\geq \rho t)=-\left(\frac{\rho^2}{2}-\beta\right). $$ In this note, we confirmed this conjecture.