Active nonreciprocal attraction between motile particles in an elastic medium

Area of Science:

• Physics of complex systems
• Soft matter physics
• Biophysics

Background:

• Vibration-activated granular matter provides a model system for studying active matter.
• Self-propelled particles in elastic media can exhibit complex collective behaviors.

Purpose of the Study:

• To investigate the interaction and collective motion of self-propelled polar rods in an elastic medium.
• To develop a theoretical framework explaining the observed attraction between these rods.

Main Methods:

• Experiments on vibration-activated granular matter.
• Computer simulations of motile particles.
• Coarse-grained theoretical modeling.

Main Results:

• Observed that polar rods attract and reorient each other.
• Developed a theory describing motile particles as moving point-force densities creating elastic strains.
• Measurements qualitatively confirmed predicted displacement fields, including a |x|^{-1/2} tail.

Conclusions:

• The effective attraction arises from elastic strains generated by the rods.
• The theory provides insights into nonreciprocal sensing and pursuit behaviors.
• Findings are relevant to interactions of motile cells in biological tissues and gels.