## Is QED a gauge theory?

QED is generally regarded as the first, and simplest, physical gauge theory. The set of possible gauge transformations of the entire configuration of a given gauge theory also forms a group, the gauge group of the theory.

**What do you mean by gauge transformation?**

A gauge transformation can be broadly defined as any formal, systematic transformation of the potentials that leaves the fields invariant (although in quantum theory it can be perhaps a bit more subtle than that because of the additional degree of freedom represented by the quantum phase).

### What is gauge invariant?

The term gauge invariance refers to the property that a whole class of scalar and vector potentials, related by so-called gauge transformations, describe the same electric and magnetic fields.

**What is gauge transformation in electromagnetic theory?**

(3.91) and is an arbitrary function, leaves the and. fields unaffected. Such a transformation is known as a gauge transformation. It is evident that a gauge transformation would leave the Heisenberg equation of motion (3.88) unchanged, but would modify the time-dependent wave equation (3.89).

## Which is the best description of gauge fixing?

In the physics of gauge theories, gauge fixing (also called choosing a gauge) denotes a mathematical procedure for coping with redundant degrees of freedom in field variables. By definition, a gauge theory represents each physically distinct configuration of the system as an equivalence class of detailed local field configurations.

**How is gauge fixing used in quantum field theory?**

Judicious gauge fixing can simplify calculations immensely, but becomes progressively harder as the physical model becomes more realistic; its application to quantum field theory is fraught with complications related to renormalization, especially when the computation is continued to higher orders.

### Is the Coulomb gauge used in quantum electrodynamics?

Because of this, the Coulomb gauge is not used in covariant perturbation theory, which has become standard for the treatment of relativistic quantum field theories such as quantum electrodynamics (QED). Lorentz covariant gauges such as the Lorenz gauge are usually used in these theories.

**Are there any non Abelian theories of gauge fixing?**

Gauge fixing in non-abelian gauge theories, such as Yangâ€“Mills theory and general relativity, is a rather more complicated topic; for details see Gribov ambiguity, Faddeevâ€“Popov ghost, and frame bundle . Gauge fixing of a twisted cylinder.