The Kundu equation is a general form of integrable system that is gauge-equivalent to the mixed nonlinear Schrödinger equation. It was proposed by Anjan Kundu. as with arbitrary function and the subscripts denoting partial derivatives. Equation is shown to be reducible for the choice of to an integrable class of mixed nonlinear Schrödinger equation with cubic–quintic nonlinearity,given in a representative form Here are independent parameters, while Equation, more specifically equation is known as the Kundu equation.
A generalization of nonlinear Schroedinger equation with additional quintic nonlinerity and a nonlinear dispersive term was proposed in in the form which may be obtained from the Kundu Equation, when restricted to. The same equation, limited further to the particular case was introduced later as Eckhaus equation, following which equation is presently known as the Kundu-Ekchaus equation. The Kundu-Ekchaus equation can be reduced to the nonlinear Schroedinger equation through a nonlinear transformation of the field and known therefore to be gauge equivalent integrable systems, since they are equivalent under the gauge transformation.
Properties and Applications
The Kundu-Ekchaus equation is associated with a Lax pair, higher conserved quantity, exact soliton solution, rogue wave solution etc. Over the years various aspects of this equation, its generalizations and link with other equations have been studied. In particular, relationship of Kundu-Ekchaus equation with the Johnson's hydrodynamic equation near criticality is established, its discretizations, reduction via Lie symmetry, complex structure via Bernoulli subequation, bright and dark soliton solutions via Bäcklund transformation and Darboux transformation with the associated rogue wave solutions, are studied.
RKL equation
A multi-component generalisation of the Kundu-Ekchaus equation, known as Radhakrishnan, Kundu and Laskshmanan equation was proposed in nolinear optics for fiber optics communication through soliton pulses in a birefringent non-Kerr medium and analysed subsequently for its exact soliton solution and other aspects in a series of papers
Quantum Aspect
Though the Kundu-Ekchaus equation is gauge equivalent to the nonlinear Schroedinger equation, they differ with respect to their Hamiltonian structures and field commutation relations. The Hamiltonian operator of the Kundu-Ekchaus equation quantum field model given by and defined through the bosonic field operatorcommutation relation, is more complicated than the well-known bosonic Hamiltonian of the quantum nonlinear Schroedinger equation. Here indicates normal ordering in bosonic operators. This model corresponds to a double -function interacting Bose gas and is difficult to solve directly.
one-dimensional Anyon gas
However under a nonlinear transformation of the field the model can be transformed to i.e. in the same form as the quantum model of nonlinear Schroedinger equation, though it differs from the NLSE in its contents, since now the fields involved are no longer bosonic operators but exhibit anyon like properties etc. where for though at the coinciding points the bosonic commutation relation still holds. In analogy with the Lieb Limiger model of function bose gas, the quantum Kundu-Ekchaus model in the N-particle sector therefore corresponds to a one-dimensional anyon gas interacting via a function interaction. This model of interacting anyon gas was proposed and exactly solved by the Bethe ansatz in and this basic anyon model is studied further for investigating various aspects of the 1D anyon gas as well as extended in different directions
