Generic power laws in higher-dimensional lattice models with multidirectional hopping

Abstract: We show that lattice models in $d>1$ dimensions with mass-conserving and multidirectional hopping dynamics exhibit power-law correlations for generic parameter values, even {\it far} from phase transition point (if any). The key idea for generating the algebraic decay is the notion of {\it multidirectional} hopping, which means that several chunks of masses, or several particles, can hop out simultaneously from a lattice site in multiple directions, consequently breaking detailed balance. Notably, the systems are described by continuous-time Markov jump processes, are diffusive, {\it lattice-rotation symmetric}, spatially homogeneous and thus have {\it no} net mass current. Using hydrodynamic and exact microscopic theory, we show that, in dimensions $d > 1$, the steady-state static density-density and ``activity''-density correlations in the thermodynamic limit decay {\it universally} as $\sim 1/r^{(d+2)}$ at large distance $r=|{\bf r}|$; the strength of the power law is exactly calculated for several models and expressed in terms of the bulk-diffusion coefficient and mobility tensor. In particular, our theory explains why center-of-mass-conserving dynamics, used to model disordered {\it hyperuniform} state of matter, should result in generic long-ranged correlations in the systems.