New integrable hierarchies gauge generated from constrained KP

Exploiting the residual gauge freedom in the formulation of constrained KP hierarchy a number of new integrable systems are derived including hierarchies of Kundu-Eckhaus equation and higher order nonlinear extensions of Yajima-Oikawa and Melnikov hierarchy. In the multicomponent case such gauge freedom generates novel multicomponent as well as vector generalisations of the above systems, while the constrained modified KP hierarchy is found to yield another set of equations like derivative NLS, Gerdjikov-Ivanov equation and chen-Lee-Liu equation depending on the gauge choice.