Functional Renormalization Group flows as diffusive Hamilton-Jacobi-type equations

Abstract: In this work, we suggest to identify the Functional Renormalization Group flow equations of two-point functions as Hamilton-Jacobi(-Bellman)-type partial differential equations. This reformulation and reinterpretation goes beyond recent developments that treat Renormalization Group flow equations as conservation laws in field space and also allows to systematically understand and handle the nonconservative contributions in flow equations numerically. We demonstrate this novel approach by first applying it to a simple fermion-boson system in zero spacetime dimensions - which itself presents as an interesting playground for method development. Afterwards, we show, how the gained insights can be transferred to more realistic systems: One is the bosonic $\mathbb{Z}_2$-symmetric model in three Euclidean dimensions within a truncation that involves the field-dependent effective potential and field-dependent wave-function renormalization. The other example is the $(1 + 1)$-dimensional Gross-Neveu model within a truncation that involves a field-dependent potential and a field-dependent fermion mass/Yukawa coupling at nonzero temperature, chemical potential, and finite fermion number.