First passage properties of asymmetric L\'evy flights

TL;DR

This paper investigates the first-passage time properties of asymmetric Lévy flights in one-dimensional domains, employing analytical and numerical methods to understand their efficiency as search strategies.

Contribution

It provides a comprehensive analysis of first-passage times for asymmetric Lévy flights using space-fractional diffusion equations and Langevin equations, highlighting their complementary strengths.

Findings

Analytical expressions for first-passage time distributions are derived.

Numerical results agree well with analytical predictions.

Asymmetry and stability index significantly influence first-passage properties.

Abstract

L\'evy Flights are paradigmatic generalised random walk processes, in which the independent stationary increments---the "jump lengths"---are drawn from an $\alpha$-stable jump length distribution with long-tailed, power-law asymptote. As a result, the variance of L\'evy Flights diverges and the trajectory is characterised by occasional extremely long jumps. Such long jumps significantly decrease the probability to revisit previous points of visitation, rendering L\'evy Flights efficient search processes in one and two dimensions. To further quantify their precise property as random search strategies we here study the first-passage time properties of L\'evy Flights in one-dimensional semi-infinite and bounded domains for symmetric and asymmetric jump length distributions. To obtain the full probability density function of first-passage times for these cases we employ two complementary methods. One approach is based on the space-fractional diffusion equation for the probability density function, from which the survival probability is obtained for different values of the stable index $\alpha$ and the skewness (asymmetry) parameter $\beta$. The other approach is based on the stochastic Langevin equation with $\alpha$-stable driving noise. Both methods have their advantages and disadvantages for explicit calculations and numerical evaluation, and the complementary approach involving both methods will be profitable for concrete applications. We also make use of the Skorokhod theorem for processes with independent increments and demonstrate that the numerical results are in good agreement with the analytical expressions for the probability density function of the first-passage times.