“…no violation of the CP-symmetry has ever been seen in any experiment involving only the strong interaction. As there is no known reason in QCD for it to necessarily be conserved, this is a “fine tuning” problem known as the strong CP problem.”
“The strong CP problem is sometimes regarded as an unsolved problem in physics, and has been referred to as “the most underrated puzzle in all of physics.” There are several proposed solutions to solve the strong CP problem. The most well-known is Peccei–Quinn theory, involving new pseudoscalar particles called axions.”from Wikipedia, Strong CP Problem, retrieved 5 December 2022
Currently the big bang cosmology advocates have a singularity whereby continuity, symmetry and harmony remain undefined. An alternative model of the universe which is affectionately known as “The Quiet Expansion” has as its backbone continuity-symmetry-harmony and fine-tuning is built into the thrust of the theory. It is a thrust for perfection knowing full well there are geometries of imperfection, also known as quantum fluctuations that create tensions, uniqueness, and unpredictability.
“The strong CP problem is solved automatically if one of the quarks is massless. In that case one can perform a set of chiral transformations on all the massive quark fields to get rid of their complex mass phases and then perform another chiral transformation on the massless quark field to eliminate the residual θ-term without also introducing a complex mass term for that field. This then gets rid of all CP violating terms in the theory.”from Wikipedia, Strong CP Problem, retrieved 5 December 2022
This is a first draft as of December 5, 2022. – Bruce E. Camber
References & Resources:
A survey of spherically symmetric spacetimes (PDF), Alan R. Parry, Analysis and Mathematical Physics volume 4, pages333–375 (2014) https://link.springer.com/article/10.1007/s13324-014-0085-x