Berlin 2015 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 26: Focus Session: Percolation and turbulent transition

DY 26.1: Invited Talk

Wednesday, March 18, 2015, 09:30–10:00, BH-N 243

Elusiveness of experimental evidence for directed percolation critical behavior — •Hugues Chaté — CEA-Saclay, Service de Physique de l’Etat Condensé, CNRS UMR 3680, Gif-sur-Yvette, France

The directed percolation universality class contains all generic continuous phase transitions into an absorbing state. It should in principle be observed in situations where an ‘active’ state is in an effectively-stochastic local competition with an ‘absorbing’ state from which no fluctuation allows to escape.

Such situations a priori abound: fires, epidemics, various invasion and front propagation processes, etc. In 1986, Pomeau even made the bold claim that the statistical, large-scale, properties of subcritical transitions to turbulence in shear flows, such as the plane Couette flow, should fall into the directed percolation class.

Hundreds of models have been shown to exhibit the universal critical behavior of directed percolation, which is also well understood at the field-theoretical level. Yet, comprehensive, unambiguous experimental evidence for it remains scarce.

In this talk, I will present this situation in more detail and discuss the reasons why experimental evidence for directed percolation scaling remains so elusive. I will describe the only fully-convincing case found by Takeuchi et al. in 2007. I will conclude with a cautious but optimistic viewpoint for the case of shear flows: almost thirty years after Pomeau’s conjecture, we may finally be near obtaining confirmation that his seminal insight was well-founded.