Extinction rates for fluctuation-induced metastabilities: A real-space WKB approach

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Abstract

The extinction of a single species due to demographic stochasticity is analyzed. The discrete nature of the individual agents and the Poissonian noise related to the birth-death processes result in local extinction of a metastable population, as the system hits the absorbing state. The Fokker-Planck formulation of that problem fails to capture the statistics of large deviations from the metastable state, while approximations appropriate close to the absorbing state become, in general, invalid as the population becomes large. To connect these two regimes, a real space WKB method based on the master equation is presented, and is shown to yield an excellent approximation for the decay rate and the extreme events statistics all the way down to the absorbing state. The details of the underlying microscopic process, smeared out in a mean field treatment, are shown to be crucial for an exact determination of the extinction exponent. This general scheme is shown to reproduce the known results in the field, to yield new corollaries and to fit quite precisely the numerical solutions. Moreover it allows for systematic improvement via a series expansion where the small parameter is the inverse of the number of individuals in the metastable state.

Original languageEnglish
Pages (from-to)861-886
Number of pages26
JournalJournal of Statistical Physics
Volume127
Issue number5
DOIs
StatePublished - Jun 2007

Bibliographical note

Funding Information:
The authors thank B. Meerson and M. Assaf for sharing their work prior to publication. The work of DAK is supported in part by the Israel Science Foundation. The work of NMS is supported in part by the EU 6th framework CO3 pathfinder.

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