Undular diffusion in nonlinear sigma models

Abstract

We discuss general features of charge transport in non-relativistic classical field theories invariant under non-abelian unitary Lie groups by examining the full structure of two-point dynamical correlation functions in grand-canonical ensembles at finite charge densities (polarized ensembles). Upon explicit breaking of non-abelian symmetry, two distinct transport laws characterized by dynamical exponent $z=2$ arise. While in the unbroken symmetry sector the Cartan fields exhibit normal diffusion, the transversal sectors governed by the nonlinear analogues of Goldstone modes disclose an unconventional law of diffusion characterized by a complex diffusion constant and undulating patterns in the spatiotemporal correlation profiles. In the limit of strong polarization, one retrieves the imaginary-time diffusion for uncoupled linear Goldstone modes, whereas for weak polarizations the imaginary component of the diffusion constant becomes small. In models of higher rank symmetry, we prove absence of dynamical correlations among distinct transversal sectors.

Presentation made less technical, 4.5 pages, 2 figures

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Cited by in corpus (5)

• Superdiffusion in spin chains
• Superuniversality of superdiffusion
• Hydrodynamics in lattice models with continuous non-Abelian symmetries
• Absence of Normal Fluctuations in an Integrable Magnet
• Hydrodynamic projections and the emergence of linearised Euler equations in one-dimensional isolated systems