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December 2020 Stochastic methods for the neutron transport equation I: Linear semigroup asymptotics
Emma Horton, Andreas E. Kyprianou, Denis Villemonais
Ann. Appl. Probab. 30(6): 2573-2612 (December 2020). DOI: 10.1214/20-AAP1567


The neutron transport equation (NTE) describes the flux of neutrons through an inhomogeneous fissile medium. In this paper, we reconnect the NTE to the physical model of the spatial Markov branching process which describes the process of nuclear fission, transport, scattering, and absorption. By reformulating the NTE in its mild form and identifying its solution as an expectation semigroup, we use modern techniques to develop a Perron–Fröbenius (PF) type decomposition, showing that growth is dominated by a leading eigenfunction and its associated left and right eigenfunctions. In the spirit of results for spatial branching and fragmentation processes, we use our PF decomposition to show the existence of an intrinsic martingale and associated spine decomposition. Moreover, we show how criticality in the PF decomposition dictates the convergence of the intrinsic martingale. The mathematical difficulties in this context come about through unusual piecewise linear motion of particles coupled with an infinite type-space which is taken as neutron velocity. The fundamental nature of our PF decomposition also plays out in accompanying work (Harris, Horton and Kyprianou (2020), Cox et al. (2020)).


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Emma Horton. Andreas E. Kyprianou. Denis Villemonais. "Stochastic methods for the neutron transport equation I: Linear semigroup asymptotics." Ann. Appl. Probab. 30 (6) 2573 - 2612, December 2020.


Received: 1 January 2019; Revised: 1 November 2019; Published: December 2020
First available in Project Euclid: 14 December 2020

Digital Object Identifier: 10.1214/20-AAP1567

Primary: 60J75, 60J80, 82D75
Secondary: 60J99

Rights: Copyright © 2020 Institute of Mathematical Statistics


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Vol.30 • No. 6 • December 2020
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