The Kardar-Parisi-Zhang (KPZ) Universality of Random Growing Interfaces

The project concerns universal large-scale behavior of random growing interfaces, which are mathematical models that describe real physical processes such as propagating fire fronts, growing liquid crystals, bacterial colonies and coffee stains. These processes are typically modeled using the statistical mechanics approach, i.e. by considering large systems of interacting particles, where each particle corresponds to a molecule or an individual bacterium. Imprecision of our measurements and dependence of physical processes on many factors are typically described by random perturbations of particles. Large-scale behavior of such models is observed when one looks at the systems from a sufficiently large distance, after a sufficiently long period of time. Universality in this case refers to the fact that such growing interfaces exhibit similar large-scale behavior. Description of this universal behavior gives a better understanding of the real physical processes in nature. Recent breakthroughs in probability theory, particularly in stochastic partial differential equations and integrable probability, have provided the tools to study such mathematical models. The Kardar-Parisi-Zhang (KPZ) universality arises in non-equilibrium statistical mechanics, when studying limiting behavior of random growing interfaces. On the mathematical level, growing interfaces appear in free energies of directed random polymers, random growth models, interacting particle systems, stochastic Burgers and Hamilton-Jacobi-Bellman equations, and stochastically perturbed reaction-diffusion equations. Depending on the characteristics of models, two universal objects are conjectured to govern such interfaces: the KPZ equation and the KPZ fixed point. Recent developments in the area of stochastic PDEs allow to prove scaling limits of various discrete systems to singular stochastic PDEs. Moreover, methods of integrable probability (exactly solvable models) provided a complete characterization of the KPZ fixed point. The goal of this project is to study universal scaling limits of such random growing interfaces using these new results. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.