Gauge theories for fluids in 2 + 1 dimensions through master actions

Two actions which are functionals of different variables but describing the same dynamical system can be shown to possess the same origin by constructing a master action which generates both of them. We first present the master action which produces an action depending on the fluid variables and a gauge theory action whose equations of motion are equivalent to the incompressible fluid Euler equations in 2+1 dimensions. We then introduce the master action generating the actions which on shell provide the linearized shallow water equations. One of them is a functional of the variables of the shallow water and the other one is the Maxwell-Chern-Simons gauge theory action. The maps between gauge vector fields and fluid variables are obtained for both of the systems. We employ them to derive the corresponding gauge theory solutions of the Hopfion and the coastal Kelvin wave solutions.