  This article consists of two parts. The main objectives of Part 1 are to
postulate a new principle of representation invariance (PRI), and to refine the
unified field model of four interactions, derived using the principle of
interaction dynamics (PID). Intuitively, PID takes the variation of the action
functional under energy-momentum conservation constraint, and PRI requires that
physical laws be independent of representations of the gauge groups. One
important outcome of this field model is a natural duality between the
interacting fields and the adjoint bosonic fields. This duality predicts two
Higgs particles of similar mass with one due to weak interaction and the other
due to strong interaction. The field model can be naturally decoupled to study
individual interactions, leading to 1) modified Einstein equations, giving rise
to a unified theory for dark matter and dark energy, 2) three levels of strong
interaction potentials for quark, nucleon/hadron, and atom respectively, and 3)
two weak interaction potentials. These potential/force formulas offer a clear
mechanism for both quark confinement and asymptotic freedom. The main
objectives of Part 2 are 1) to propose a sub-leptons and sub-quark model, which
we call weakton model, and 2) to derive a mechanism for all sub-atomic decays
and bremsstrahlung. The weakton model postulates that all matter particles and
mediators are made up of massless weaktons. The weakton model offers a perfect
explanation for all sub-atomic decays and all generation/annihilation precesses
of matter-antimatter. In particular, the precise constituents of particles
involved in all decays both before and after the reaction can now be precisely
derived. In addition, the bremsstrahlung phenomena can be understood using the
weakton model. Also, the weakton model offers an explanation to the baryon
asymmetry problem.
