The work performed during the project has been divided into three parts as described below:
(i) In this work we explore glassy dynamics of dense assemblies of soft particles that are self-propelled by active forces. These forces have a fixed amplitude and a propulsion direction that varies on a timescale known as the the persistence timescale. Numerical simulations of such active glasses are computationally challenging when the dynamics is governed by large persistence times. We describe in detail our recently proposed scheme that allows one to study directly the dynamics in the large persistence time limit, on timescales around and well above the persistence time. We establish that our prescription faithfully reproduces all dynamical quantities in the appropriate limit when persistence time becomes extremely large.
The results has been published in: How to study a persistent active glassy system, R. Mandal and P. Sollich, J. Phys.: Condens. Matter, 33, 184001 (2021).
(ii) To explore the rheological response of such dense active matter system we employed extensive molecular dynamics simulation and a few distinct dynamical and mechanical order parameters. We have been able to differentiate three dynamical steady states in a sheared model active glassy system: 1) a disordered state, 2) a propulsion-induced ordered state, and 3) a shear-induced ordered state. We supplement these observations and make testable predictions for the joint distribution of single-particle position and orientation. with an analytical theory based on an effective single-particle Fokker–Planck description (with parameters that can be measured independently) to rationalize the existence of the shear-induced orientational ordering behavior in an active glassy system without explicit aligning interactions of, for example, Vicsek type. This ordering phenomenon occurs in the large persistence time limit and is made possible only by the applied steady shear.
The results has been published in: Shear Induced Orientational Ordering in an Active Glass Former, R. Mandal and P. Sollich, Proc. Natl. Acad. Sci., 118 (39) (2021).
(iii) To understand these dense active/living systems better we extended the active random first-order transition theory (ARFOT) in the high activity regime using an activity-dependent harmonic confining potential, which we solve self-consistently. The extended model predicts qualitative changes in the high activity regime, which agree with the results of simulations in both three-dimensional and two-dimensional models of active glass.
The results has been published in: The random first-order transition theory of active glass in the high-activity regime, R. Mandal, S.K. Nandi, C. Dasgupta, P. Sollich, Nir. S. Gov, J. Phys. Commun. 6 115001 (2022).
Also the results have been shared with the scientific community and beyond via Twitter, press release and scientific seminar, some of which are mentioned below:
Statistical Physics Webinar, Dept. of Phys. and Mat. Sci., Uni-Luxembourg, Luxembourg (2021)
Random Interactions Webinar, Department of Theoretical Physics, TIFR, India (2022).
German Physical Society (DPG) meeting at Regensburg, Germany (2022).
