Progress in Quasihydrodynamics

Hydrodynamics is the study of interacting systems at late times and large distances. Applying this framework to a generic system requires that the only degrees of freedom that remain relevant at these scales are those associated with conservation of the “hydrodynamic charges” such as energy, momentum or particle number.

Spurred by discoveries in high energy physics (in particular gauge-gravity dualities), there has been much recent work in understanding and obtaining the formal structure of hydrodynamic constitutive relations. For example, it is now understood how to obtain dissipative constitutive relations from a variational principle via the “Schwinger-Keldysh” formalism. Moreover, this programme has led to the development of hydrodynamic descriptions for some rather exotic states of matter (such as strange metals, Weyl semi-metals etc.).

A sister theory to hydrodynamics is quasihydrodynamics. This represents a modification of hydrodynamics where energy, momentum and particle number are no longer conserved, but decay very slowly. Quasihydrodynamics is much less well understood, but is necessary if hydrodynamics is to be a good description of certain exotic states of matter.

In this poster I will review the progress that has been made into understanding the structure of quasihydrodynamics. I will summarise recent work and indicate where open questions remain.