  General Yang-Mills symmetry and Yang-Mills gravity in inertial frames
presents a possible avenue for understanding dark energy phenomenon in terms of
the extremely small baryon charges of protons and neutrons. General gauge
transformations involve vector gauge functions and Hamilton's characteristic
phase functions rather than scalar gauge functions and usual phase functions.
One has fourth-order gauge field equations, which lead to a static linear
potential between two point baryonic charges. Together with gravitational
force, the model predicts that in the early universe, when the gravitational
force was dominant, not only was the expansion occurring at a decreasing rate,
the rate of change of the deceleration was decreasing due to a $1/r^2$
dependence. In the present universe, when the baryonic force is dominant, the
cosmic acceleration should be approximately constant and has a maximum value
$a_{max}\approx 10^{-13} m/s^2$, as measured in an inertial frame. We hope that
these properties of the late-time cosmic acceleration can be tested in the
future.
