Orateur
Description
Active particles are self-propelled units that continuously convert energy into directed motion, making them paradigmatic examples of far-from-equilibrium systems. Their intrinsic non-equilibrium nature gives rise to a wide range of collective phenomena, including flocking, pattern formation, and non-equilibrium phase transitions. Despite significant progress, a fundamental understanding of the emergent large-scale behavior of active matter remains a central challenge in statistical physics. In this talk, I will present recent theoretical advances in the hydrodynamic description of polar active fluids and the role of thermodynamic constraints in shaping their collective dynamics. Building on the formalism of fluids without boost symmetry, I will show that polar active fluids can be mapped onto passive fluids supplemented by non-thermal noise and symmetry-breaking constraints, without modifying the underlying thermodynamic relations. This framework allows for the derivation of exact scaling exponents for transport coefficients under dynamical renormalization group flow in arbitrary spatial dimension d. The resulting critical exponents smoothly interpolate between mean-field predictions and recent high-precision numerical results for flocking models, providing a unified picture that reconciles analytical theory with simulations and experiments. Time permitting, I will discuss how this paradigm can be generalized to novel fixed points in more complex active systems. In particular, I will consider two examples: (i) active systems exhibiting autochemotaxis, where self-propelled particles move coherently while emitting an attractive chemical field, and (ii) active systems in which both activity and inertia play a crucial role. In the latter case, I will show how spin-hydrodynamic techniques provide a powerful framework to characterize the resulting phases and their collective dynamics.
