Smallest scale of practial perturbative expantion?

[MTd2]

It seems that Chiral perturbation theory is valid between 100MeV and 1GeV, perturbative qcd, above ~5GeV. So, is there any method that works in good approximation bellow 100MeV, besides lattice methods? What about the interval between 1GeV and 5Gev?

I read at ressonaances blog http://resonaances.blogspot.com/2011/11/lhcb-has-evidence-of-new-physics-maybe.html , that the region right above 1GeV is now man`s land, which might explain the bigger than expected charm CP violation. What method is usually used around these values?

 

[LightHero]

In the energy range between 100MeV and 1GeV, effective field theory (EFT) is often used. This is an approach that allows one to take into account the effects of interactions between particles without having to calculate the full quantum field theory. This is done by introducing "effective" interactions which describe the behavior of the system in a certain energy regime. These effective interactions can then be used to calculate various observables such as cross sections, decay rates, and other particle properties. In this way, EFT can provide a good approximation of the behavior of the system in the regime below 1GeV. In the energy range between 1GeV and 5GeV, perturbative QCD (pQCD) is used. This is an approach that uses Feynman diagrams to calculate the interaction between particles. This allows for a more accurate calculation of cross sections, decay rates, and other particle properties. pQCD also allows for the inclusion of higher order corrections which can improve the accuracy of the calculations.The region right above 1GeV is known as the "man's land", as it is not well understood and few theoretical methods have been established to calculate properties of particles in this energy range. However, there are some approaches that have been developed, such as the Green's function Monte Carlo method, which can be used to calculate cross sections and other particle properties with good accuracy.