Within Yang-Mills gravity with translation group T (4) in flat space-time, the invariant action involving quadratic translation gauge-curvature leads to quadrupole radiations which are shown to be consistent with experiments. The radiation power turns out to be the same as that in Einstein's gravity to the second-order approximation. We also discuss an interesting physical reason for the accelerated cosmic expansion based on the long-range Lee-Yang force of U b (1) gauge field associated with the established conservation law of baryon number. We show that the Lee-Yang force can be related to a linear potential ∝ r, provided the gauge field satisfies a fourth-order differential equation. Furthermore, we consider an experimental test of the Lee-Yang force related to the accelerated cosmic expansion. The necessity of generalizing Lorentz transformations for accelerated frames of reference and accelerated Wu-Doppler effects are briefly discussed.

The S-matrix, its unitarity and the graviton self-energy at the one-loop level are discussed on the basis of quantum Yang-Mills gravity with the translational gauge symmetry in flat space-time. The unitarity and gauge invariance of the S-matrix in a class of gauge conditions is preserved by massless ghost vector particles, called 'Feynman-DeWitt-Mandelstam' (FDM) ghosts, in quantum Yang-Mills gravity. Using dimensional regularization, the graviton self-energy are explicitly calculated with a general gauge condition. The resultant divergence of graviton self-energy at the one-loop level resembles to that in quantum electrodynamics.In memory of Ching-Chiang Chen, who introduced JP to Utiyama's exciting idea about gravity based on Yang-Mills gauge symmetry during our college years. *

Based on a generalized Yang-Mills framework, gravitational and strong interactions can be unified in analogy with the unification in the electroweak theory. By gauging T(4) × [SU(3)]color in flat space-time, we have a unified model of chromo-gravity with a new tensor gauge field, which couples universally to all gluons, quarks and anti-quarks. The space-time translational gauge symmetry assures that all wave equations of quarks and gluons reduce to a Hamilton-Jacobi equation with the same ‘effective Riemann metric tensors’ in the geometric-optics (or classical) limit. The emergence of effective metric tensors in the classical limit is essential for the unified model to agree with experiments. The unified model suggests that all gravitational, strong and electroweak interactions appear to be dictated by gauge symmetries in the generalized Yang-Mills framework.