Microscopic and macroscopic descriptions of a Vicsek-Kuramoto model
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In this work, we study an individual-based model (IBM) for self-propelled agents interacting through alignment mechanisms and analyze its macroscopic behavior via formal asymptotic limits. The model extends the Persistent Turning Walker with Alignment (PTWA) framework, initially introduced to describe curvature-driven collective motion in biological systems such as schooling fish. It incorporates key features of both the Kuramoto and Vicsek models: phase synchronization is governed by intrinsic angular velocity dynamics in the spirit of the Kuramoto model, while alignment interactions are restricted to spatially localized neighborhoods, as in the Vicsek model. We derive the corresponding mean-field kinetic equation and investigate its hydrodynamic limit. A central challenge lies in the absence of conserved quantities such as momentum and energy. To overcome this, we employ the concept of generalized collisional invariants (GCIs), which allows us to close the system and derive a macroscopic model. The resulting hydrodynamic system comprises a continuity equation for the particle density, a conservative equation for the angular momentum density, and a non-conservative evolution equation for the mean orientation. Numerical simulations are used to compare the qualitative behavior of the model at different scales. In particular, we examine emergent patterns such as traveling waves in the orientation field and global oscil- latory dynamics at the microscopic level, and assess their consistency with the macroscopic predictions. This multiscale approach provides new insight into how interactions based on angular velocity relaxation contribute to the emergence of coherent large-scale structures in active matter systems. These findings are particularly relevant for modeling dense suspensions of self-propelled biological agents, such as sperm cells and bacterial colonies.
