Quantum field theory (QFT) provides a framework for describing and quantizing fields, including electromagnetic, strong nuclear, and weak nuclear forces, as well as matter particles. In QFT, various quantities can be measured or computed to describe the behavior and properties of particles and fields. Here are some of the key quantities in QFT:
Particle Number: QFT allows us to determine the number of particles in a given state. The number of particles can be measured using detectors or inferred from scattering experiments.
Energy and Momentum: QFT enables the calculation of energy and momentum distributions of particles and fields. These quantities can be measured in experiments, such as particle collisions or interactions.
Cross Sections: Cross sections describe the likelihood of particle interactions or scattering events. QFT allows the calculation and prediction of cross sections, which can be compared with experimental measurements to test the theory.
Decay Rates: Quantum field theory allows the computation of decay rates for unstable particles. These rates describe the probability of a particle decaying into specific final states and can be compared with experimental observations.
Scattering Amplitudes: Scattering amplitudes describe the probability amplitudes for particles to scatter or interact. They can be computed using perturbative methods in QFT and compared with experimental data.
Correlation Functions: Correlation functions in QFT provide information about the correlations between observables in a quantum system. They can be used to study the behavior of fields and particles and extract information about their properties.
Vacuum Expectation Values: In QFT, vacuum expectation values represent the average values of fields in the vacuum state. These values can provide insights into the ground state properties and the presence of particle-antiparticle pairs.
Symmetry Breaking and Order Parameters: Quantum field theory allows the study of symmetry breaking and the associated order parameters. These quantities are important for understanding phase transitions and the emergence of different phases of matter.
It's worth noting that the specific quantities measurable in QFT depend on the particular field theory under consideration and the experimental techniques available. QFT provides a powerful theoretical framework for calculating and predicting these quantities, which can then be compared with experimental measurements to test and refine the theory.