Seminars

The Theory Club seminar series

If you are interested, please contact ada.altieri@u-paris.fr to be added to the mailing list 


 09/07/24 -  Giulia Pisegna

 Emergent polar order in non-polar mixtures with non-reciprocal interactions

Phenomenological rules that govern the collective behaviour of complex physical systems are powerful tools because they can make concrete predictions about their universality class based on generic considerations, such as symmetries, conservation laws, and dimensionality. While in most cases such considerations are manifestly ingrained in the constituents, novel phenomenology can emerge when composite units associated with emergent symmetries dominate the behaviour of the system. I will present the study of a generic class of active matter systems with non-reciprocal interactions where we demonstrate the existence of true long-range polar order in two dimensions and above, both at the linear level and by including all relevant nonlinearities in the Renormalization Group sense. We achieve this by uncovering a mapping of our scalar active mixture theory to the Toner-Tu theory of dry polar active matter by employing a suitably defined polar order parameter. I will then show that the complete effective field theory of fluctuations -- which includes all the soft modes and the relevant nonlinear terms -- belongs to the (Burgers-) Kardar-Parisi-Zhang universality class. This classification allows us to prove the stability of the emergent polar long-range order in scalar non-reciprocal mixtures in two dimensions, and hence a conclusive violation of the Mermin-Wagner theorem. Finally, I will briefly show how to extend this dry system to a wet case, where hydrodynamic interactions are taken into consideration in the presence of a momentum-conserving fluid. The mapping to a polar active fluid is again crucial to uncover a fluid mediated linear instability for traveling waves.

18/06/24 -  Aparna Baskaran 

From molecules to moduli : Data driven approaches to controlling active nematics

This talk will describe recent attempts at building quantitative theories of active nematics guided by experimental data.  Two examples will be considered - a confined 3D flow aligned fluid and a 2D bulk fluid. Further, some ongoing work on optimal control theory for control of active flows will be discussed.

17/06/24 -  Anna Poggialini

Novel Approaches in Network Analysis and Dynamical Systems Modeling

In this talk, I will provide an overview of my recent research. The first part focuses on the main line of my thesis project, exploring network theory issues using the formalism of statistical mechanics. 

The recent Laplacian renormalization group [1] has introduced a new perspective on treating networks within this framework, opening up several research avenues. Notably, we developed a community detection method that resolves information aggregation in networks at various resolutions [2]. We also investigated nodes that act as bottlenecks for temporal diffusion, proposing an alternative centrality measure. This measure connects with the fluctuation dissipation theorem, analogized with the Laplacian formalism. 

Additionally, we identified new methods for detecting spectral dimensions, which under certain conditions, are related to the specific heat of graphs. 

The second part briefly covers part of my research on dynamical systems. The project I would like to share aims to describe the dynamical effects of feed-forward and cyclic coupling structures in a modified Wilson-Cowan model.

[1] Villegas, P., Gili, T., Caldarelli, G. et al. Laplacian renormalization group for heterogeneous networks. Nat. Phys. 19, 445–450 (2023)

[2] arXiv:2301.04514

Full List of speakers ( from September 2023 )