Fluid Mechanics of Strings
We consider conserved currents in an interacting network of one-dimensional objects (or strings). Singular currents localized on a single string are considered in general, and a formal procedure for coarse-graining over many strings is developed. This procedure is applied to strings described by the Nambu-Goto action such as cosmic strings. In addition to conserved currents corresponding to the energy-momentum tensor, we obtain conserved currents corresponding to an antisymmetric tensor hF µ� i = hx ′µ u x � − u x µ x ′� i, where u x µ and x ′µ are the velocity and tangent vectors of strings. Under the assumption of local equilibrium we derive a complete set of hydrodynamic equations for strings.