asimov42 said:could someone explain why a real, 'observable' particle is said to be 'off-shell' in an external field?
Off shell just means that the standard asymptotic (or free field) relation $p^2=m^2$ (in units where $c=1$), which defines the on shell condition, is not satisfied.asimov42 said:Or is the use of 'off shell' in this case simply to indicate that the field may influence the energy of the particle?
An 'off-shell' particle is a term used in particle physics to describe a particle that does not satisfy the equations of motion for a free particle. This means that the particle is not moving in a way that is consistent with its mass and energy.
An external field can cause an 'off-shell' particle to deviate from its expected behavior. This can be due to interactions with other particles or the presence of a strong electromagnetic or gravitational field.
Studying 'off-shell' particles can provide valuable insights into the underlying physics of particle interactions. It can also help us better understand the effects of external fields on particle behavior and potentially lead to new discoveries.
Scientists use sophisticated detectors, such as particle accelerators, to study 'off-shell' particles. These detectors can measure the properties of particles, such as their mass and energy, and track their movements in an external field.
Understanding 'off-shell' particles is crucial for many areas of modern technology, such as medical imaging and nuclear energy. It also has implications for fundamental physics research, including the search for new particles and the development of new theories to explain the behavior of matter and energy.