Smallest scale of practial perturbative expantion?

• MTd2
In summary, effective field theory and perturbative QCD are used to study particle interactions in the energy ranges below and above 1GeV, respectively. In the "man's land" region, other methods such as Green's function Monte Carlo may also be employed.
MTd2
Gold Member
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?

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.

1. What is the smallest scale of practical perturbative expansion?

The smallest scale of practical perturbative expansion refers to the limit at which perturbative methods can still accurately describe physical phenomena. This scale is typically determined by the strength of the interactions between particles, with weaker interactions allowing for a larger range of applicability for perturbative techniques.

2. How is the smallest scale of practical perturbative expansion calculated?

The smallest scale of practical perturbative expansion is calculated using a combination of theoretical calculations and experimental data. Theoretical calculations involve solving equations that describe the behavior of particles at different energy scales, while experimental data provides confirmation of these theoretical predictions.

3. Why is the smallest scale of practical perturbative expansion important?

The smallest scale of practical perturbative expansion is important because it allows scientists to make accurate predictions about the behavior of particles at different energy scales. This information is crucial for understanding the fundamental laws of nature and for developing new technologies.

4. What are the limitations of the smallest scale of practical perturbative expansion?

The limitations of the smallest scale of practical perturbative expansion include the assumption that interactions between particles are weak, which may not always be the case at high energy scales. Additionally, perturbative methods may break down in extreme conditions, such as near black holes or in the early universe.

5. How does the smallest scale of practical perturbative expansion relate to the Standard Model of particle physics?

The smallest scale of practical perturbative expansion is a key concept in the Standard Model of particle physics, as it helps to define the range of applicability for the theory. The Standard Model is successful in describing particles and their interactions at energy scales below the smallest scale of practical perturbative expansion, but it is believed that new physics will be necessary to describe phenomena at higher energy scales.