Renormalisation, dynamics, and hyperbolic symmetry

ended

The objective of this proposal is to develop effective methods for the analysis of classical continuous spin systems, with focus on their stochastic dynamics and on spin systems with hyperbolic symmetry. The latter are related to reinforced random walks and to random operators. In particular, I propose to develop mathematical methods for renormalisation group analysis of such systems. Renormalisation is a central concept in theoretical physics, explaining a vast range of phenomena heuristically. While its rigorous implementation is difficult, when a renormalisation group approach to a problem is available, it provides very detailed control and also explains universality. Both, in stochastic dynamics of large scale systems and in random matrix theory, great progress has been achieved recently. In stochastic dynamics, this applies in particular to the problem of existence of solutions to SPDEs and their regularity (ultraviolet problem). This proposal focuses on the complementary regime of long time asymptotics (infrared problem), where important results have been obtained via exact solutions but robust methods remain scarce. In random matrix theory, very general classes of random matrices have been understood, yet those with finite dimensional structure like the Anderson model remain out of reach. Spin systems with hyperbolic symmetry and supersymmetry arise in the descriptions of such random matrices, and their simplified versions are prototypes for the understanding of the original models. They also describe linearly reinforced random walks which are of independent interest, and allow for some of the quantum phenomena to be reinterpreted probabilistically. I will build on methods that I developed in previous work, including renormalisation group analysis for static systems, the development of a renormalisation group approach to Glauber dynamics, the study of spin systems with hyperbolic symmetry and supersymmetry, and my experience in random matrix theory.