Phase transitions in optimal search times: how random walkers should combine resetting and flight scales

TL;DR

This paper demonstrates that phase transitions in optimal search times can occur in simple random walks with exponential flights and resetting, without needing Levy statistics, highlighting the importance of combining multiple movement scales.

Contribution

It shows that phase transitions in search efficiency are present in exponential flight models with resetting, providing exact analytical solutions and connecting to broader search theory concepts.

Findings

Phase transitions occur in exponential flight models with resetting.

Exact analytical solutions for MFPT are obtained.

Multiple movement scales are key to minimizing search times.

Abstract

Recent works have explored the properties of L\'evy flights with resetting in one-dimensional domains and have reported the existence of phase transitions in the phase space of parameters which minimizes the Mean First Passage Time (MFPT) through the origin [Phys. Rev. Lett. 113, 220602 (2014)]. Here we show how actually an interesting dynamics, including also phase transitions for the minimization of the MFPT, can also be obtained without invoking the use of L\'evy statistics but for the simpler case of random walks with exponentially distributed flights of constant speed. We explore this dynamics both in the case of finite and infinite domains, and for different implementations of the resetting mechanism to show that different ways to introduce resetting consistently lead to a quite similar dynamics. The use of exponential flights has the strong advantage that exact solutions can be obtained easily for the MFPT through the origin, so a complete analytical characterization of the system dynamics can be provided. Furthermore, we discuss in detail how the phase transitions observed in random walks with resetting are closely related to several ideas recurrently used in the field of random search theory, in particular to other mechanisms proposed to understand random search in space as mortal random-walks or multi-scale random-walks. As a whole we corroborate that one of the essential ingredients behind MFPT minimization lies in the combination of multiple movement scales (whatever its origin).