Dense active matter and the cage escape dynamics of active particles
Objectives
Passive particles form amorphous solids or glasses at high densities. The same is true of active particles that model living matter such as confluent tissues. For active particles, recent work [1,2] has found unusual behaviour when they have to escape from local energy minima, with non-Gaussian noise arising from activity typically speeding up escape processes, exponentially so for low noise levels. This project aims to characterise how these effects differ among distinct models of activity, including active Brownian particles, active Ornstein-Uhlenbeck and run-and-tumble particles. Although equivalent for many purposes, they are expected to show qualitative differences in the rare fluctuations required for cage escape. The second aim is to analyse how differences at the single particle level translate into qualitatively new effects in the collective behaviour of active glasses, whose relaxation dynamics rely precisely on particles escaping from cages.
Activities of the Doctoral Candidate
Analytical work will investigate the single-cell/particle escape dynamics, extending techniques developed recently for passive particles [2], which allow in principle exact solutions for effective barriers and escape trajectories in the low noise limit. To understand the effects on collective dynamics, numerical simulations will be deployed to measure local barrier statistics [3] and relate them with escape times. At the collective level, Mode-Coupling Theory [4] will be used to understand analytically the behaviour seen in numerical simulations.
Facilities Provided
Access to computing facilities for numerical work, including high performance computing.
Employment Contract
Doctoral Candidate will be employed on a standard German researcher contract (TV-L E13). Pay and other benefits will follow the general Doctoral Network conditions, see @@ add website link @@ for details.
Period of Doctorate and Funding
Period of doctorate and funding: Doctorates at University of Goettingen take between 3 and 4 years. Unspent local CAFE-BIO funds will be used to support the Doctoral Candidate in year 4 as required.
References
[1] Woillez, E et al. (2019) Phys Rev Lett 122:258001; [2] Baule, A, & Sollich, P. (2023) Sci Rep 13:3853; [3] Pica Ciamarra, M, et al. (2024) Proc Natl Acad Sci 121:e2400611121; [4] Debets, VE, et al. (2024) Phys Rev E 109:054605; Janssen, LMC. (2018) Frontiers Phys 6:97 [5] Keta, Y-E, & Henkes, S. (2025) Soft Matter 21:5710.