Fermionic back-reaction on kink and topological charge pumping in the $sl(2)$ affine Toda coupled to matter

Abstract

We explore the Faddeev-Jackiw (F-J) symplectic Hamiltonian reduction of the $sl(2)$ affine Toda model coupled to matter (ATM), which includes new parametrizations for a scalar field and a Grassmannian fermionic field. The structure of constraints and symplectic potentials primarily dictates the strong-weak dual coupling sectors of the theory, ensuring the equivalence between the Noether and topological currents. The analytical calculations encompass the fermion-kink classical solution, the excited fermion bound states localized on the kink, and the scattering states, all of which account for the fermion back-reaction on the soliton. The total energy, which includes the classical fermion-soliton interaction energy, the bound-state fermion energy, and the fermion vacuum polarization energy (VPE), is determined by the topological charge of the kink. This system satisfies first-order differential equations and a chiral current conservation equation. Our results demonstrate that the excited fermion bound states and scattering states significantly alter the properties of the kink. Notably, they give rise to a pumping mechanism for the topological charge of the in-gap kink due to fermionic back-reaction, as well as the appearance of kink states in the continuum (KIC).