A one-parameter integrable deformation of the Dirac--sinh-Gordon system

Abstract: We establish the integrability of a one-parameter family of coupled Dirac--scalar field theories in $(1+1)$ dimensions that interpolates between the known Dirac--sinh-Gordon and Dirac--sine-Gordon systems. The deformation is controlled by a phase parameter that modifies the Yukawa coupling and simultaneously rescales the scalar backreaction. For all values of the parameter, we construct an explicit zero-curvature representation based on an $sl(2,\mathbb{C})$-valued Lax pair and show that the deformation preserves integrability. We further prove that the family is physically non-trivial, in the sense that distinct parameter values are not related by admissible field redefinitions. In addition, we derive the continuity relation for the fermion bilinear, show that the spatial bilinear constraint follows from the zero-curvature equations, and construct the first conserved densities of the hierarchy. At the two endpoints, the family reduces to the standard integrable Dirac--sinh-Gordon model and, after analytic continuation, to the Dirac--sine-Gordon system which is dual to the massive Thirring model.