Solution to the cosmological constant problem from dark energy of the quark vacuum

We solve the cosmological constant puzzle by attributing its origin to gravitational self-energy of quark vacuum quantum fluctuations and to Mach-Einstein's principle of the relativity of all inertia. The Dirac sea of negative energy quarks and its fluctuations, which should be subjected to the expansion of the universe, is actually frozen because of quark-antiquark pair creation from the QCD confinement energy, which is well described by a string potential. When the members of a pair separate beyond a critical distance, the string breaks and a new pair is created, so that the density remains constant under adiabatic expansion, as required for a Lorentz invariant vacuum. We argue that the energy scale at which the vacuum no longer follows the expansion is therefore given by the effective mass of quarks in the neutral pion. This yields a predicted value of the reduced cosmological constant $\Omega_\Lambda h^2({\rm pred})=0.31152 \pm 0.00006$, which is 100 times more precise while in excellent agreement with its observational value recently determined by the 2018 {\it Planck} mission reanalysis, $\Omega_\Lambda h^2({\rm obs})=0.3153\pm 0.0065$