Soft collinear effective theory (SCET) is a framework used in theoretical physics to describe the behavior of particles that are moving at high energies and close to the speed of light. It combines the principles of quantum field theory and special relativity to provide a systematic and accurate description of the interactions between these particles.
SCET is useful in particle physics because it allows for a more precise and efficient calculation of the behavior of high-energy particles. By separating the collinear and soft components of the particles' momenta, SCET simplifies the calculations and reduces the number of Feynman diagrams that need to be considered.
SCET differs from traditional effective field theories in that it specifically focuses on the behavior of particles at high energies and near the speed of light. It also incorporates the principles of special relativity, which is not always the case in other effective field theories.
The key concepts in SCET include the factorization theorem, which separates the hard, collinear, and soft components of the particles' momenta, and the power counting scheme, which determines the relative importance of different terms in the calculations. Other important concepts include Wilson lines, soft-collinear mode, and matching calculations.
SCET has a wide range of applications in particle physics, including the study of high-energy particle collisions at accelerators, such as the Large Hadron Collider, and the calculation of scattering amplitudes in quantum chromodynamics (QCD). It is also used to study the properties of particles, such as the Higgs boson, and to search for new physics beyond the Standard Model.