15 November 2022
ICTS faculty member Sthitadhi Roy’s publication (in collaboration with Aydin Deger and Achilles Lazarides from Loughborough University), titled Constrained Dynamics and Directed Percolation, was highlighted as Editors’ Suggestion in Physics Review Letters. In October, the authors’ publication titled Arresting Classical Many-Body Chaos by Kinetic Constraints, also in PRL, was based on a related topic.
“The two papers together complete the story,” Sthitadhi said.
The butterfly effect — an infinitesimal local change in the initial condition, a wingbeat of the proverbial butterfly, can amplify exponentially and spread ballistically in spacetime to effect drastic changes in the global state at later times, such as cause a tornado in a different part of the world — captures the quintessential notion of chaos which in turn underpins much of our understanding of ergodicity. Sthitadhi and his collaborators find that kinetic constraints in the dynamics of a many-body system can arrest this spreading of information and lead the system into a non-chaotic phase where the butterfly effect is killed and in fact, the strength of the constraint drives a bonafide dynamical phase transition from a chaotic to a non-chaotic phase. Phase transitions are accompanied by ‘universality’ which is fundamentally important as the behaviour of the system becomes independent of the microscopic details. They show that the constraint-induced phase transition lies in the so-called ‘directed percolation’ universality class. This universality class finds occurrences in several other critical phenomena at very different scales such as damage spreading and epidemics.