Relativistic interactions for the meson-two-nucleon system in the clothed-particle unitary representation

The method of unitary clothing transformations put forward in relativistic quantum field theory (QFT) by Greenberg and Schweber and developed by Shirokov is applied to construct a new family of interactions in the meson-two-nucleon system. Along with a brief exposition of its basic elements we show a specific transition from the initial "bare" one-meson and one-nucleon operators and states to their physical "clothed" counterparts. We emphasize that the clothing transformations in question do not alter the original total Hamiltonian, but provides a conceptually more transparent representation of the same Hamiltonian in terms of a new set of operators for particles with physical properties and their relativistic interactions. The Hermitian and energy-independent interaction operators for the processes π N → π N, NN → NN and NN ↔ π NN are derived starting from the Yukawa-type couplings between fermions (nucleons and antinucleons) and bosons (π-, η-, ρ-, ω- mesons, etc.). These types of interaction have a distinctive off-energy-shell structure which is naturally generated by the unitary transformation that removes from the Hamiltonian the (three-leg) π NN vertex coupling.