Paul Balduf#paperOfTheDay for Tuesday: "Effective chiral Lagrangians for nucleon-pion interactions and nuclear forces" from 1991. This is one of the foundational papers of chiral effective field theory.
In principle, the interactions of nucleons (i.e. protons, neutrons), like any other interaction on small scales, is governed by the standard model of #particle physics, in particular #quantum chromodynamics. However, it is highly impractical to do calculations this way because below a certain energy (around 1GeV), the QCD force is so strong that it creates bound states, which one can not easily handle in perturbative #quantumFieldTheory . The way out is to use an effective field theory: The resulting objects, however they may arise, of course follow the usual laws of quantum mechanics, and they have certain symmetries governing their possible interactions. One takes these objects -- in the present case nucleons and pions -- as "elementary particles", writes down an ansatz for a Lagrangian, and works with this as usual.
In order to do perturbation theory, one needs a way to determine which terms are important and which are small corrections, and how the various terms scale under e.g. a change in energy. This "power counting" is more tricky in chiral effective theory than usual, because one has multiple mass scales and their ratios, but one possible way to do it is described in the paper.
https://www.sciencedirect.com/science/article/abs/pii/055032139190231L
In principle, the interactions of nucleons (i.e. protons, neutrons), like any other interaction on small scales, is governed by the standard model of #particle physics, in particular #quantum chromodynamics. However, it is highly impractical to do calculations this way because below a certain energy (around 1GeV), the QCD force is so strong that it creates bound states, which one can not easily handle in perturbative #quantumFieldTheory . The way out is to use an effective field theory: The resulting objects, however they may arise, of course follow the usual laws of quantum mechanics, and they have certain symmetries governing their possible interactions. One takes these objects -- in the present case nucleons and pions -- as "elementary particles", writes down an ansatz for a Lagrangian, and works with this as usual.
In order to do perturbation theory, one needs a way to determine which terms are important and which are small corrections, and how the various terms scale under e.g. a change in energy. This "power counting" is more tricky in chiral effective theory than usual, because one has multiple mass scales and their ratios, but one possible way to do it is described in the paper.
https://www.sciencedirect.com/science/article/abs/pii/055032139190231L