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Gustavo O. Carvalho

Publications and source records attributed to Gustavo O. Carvalho.

2 recordsLinked to original sources

The Frog Model on $\mathbb{Z}$ with Discrete Weibull Lifetimes and Random Parameter $p$

We study the frog model on $\mathbb{Z}$ with particle wise discrete Weibull lifetimes. Each particle has an i.i.d. survival parameter $π\in(0,1)$; conditionally on $π=p$, its lifetime $Ξ$ satisfies \[ P(Ξ\ge k\mid π=p)=p^{k^γ},\qquad k\in\mathbb{N}_0,γ>0. \] The law of $π$ has right edge density \[ f_π(u)\sim(1-u)^{β-1},L\big((1-u)^{-1}\big)\qquad (u\uparrow 1), \] with $β>0$ and $L$ slowly varying; let $η$ denote the common law of the i.i.d. initial occupation numbers $\{η_x\}_{x\in\mathbb{Z}}$. The survival parameter distribution strictly extends the Beta family, while the lifetime distribution extends the geometric case. We prove a sharp extinction and survival dichotomy with the $γ-$dependent threshold \[ β_c:=\frac{1}{2γ}. \] If $β>β_c$ and $E(η)<\infty$, the process becomes extinct almost surely; if $β<β_c$ and $P(η=0)<1$, it survives with positive probability. At the boundary $β=β_c$ we provide explicit criteria in terms of $\limsup/\liminf$ of $L(n^{2γ})$. The case $γ=1$ (geometric lifetimes) recovers the benchmark $β_c=\frac{1}{2}$ and the critical refinements previously obtained for random geometric lifetimes.

math.PR↗

The Frog Model on $\mathbb{Z}$ with General Random Survival Parameter

We study the frog model on $\mathbb{Z}$ with particle-wise random geometric lifetimes: each particle has a survival parameter $π\in(0,1)$ sampled i.i.d., whose density near $1$ satisfies $f_π(u)\sim (1-u)^{β-1}L\big((1-u)^{-1}\big)$ with $β>0$, and $L$ slowly varying. This strictly extends the $\mathrm{Beta}(α,β)$ case. Let $η$ denote the common law of the i.i.d.\ initial number of particles $\{η_x\}_{x\in\mathbb{Z}}$. Using a percolation comparison and sharp one-particle displacement tails, we obtain a universal threshold at $β=\tfrac12$. If $β>\tfrac12$ and $E(η)<\infty$, extinction occurs almost surely. If $β<\tfrac12$ and $\mathbb{P}(η=0)<1$, survival has positive probability. At the boundary $β=\tfrac12$ we give sharp criteria: extinction if $E(η)<\infty$ and $8\,\limsup_{n\to\infty}L(n^2)<1/E(η)$; survival if $\mathbb{P}(η=0)<1$ and $\sqrt{2}\,\liminf_{n\to\infty}L(n^2)>1/E(η)$. These results recover the Carvalho-Machado threshold for Beta laws and show that only the exponent $β$ governs the phase transition, while $L$ impacts the critical regime.

math.PR↗