QFT around fixed classical backgrounds is a theoretical framework used in quantum field theory to study the behavior of quantum fields in the presence of a fixed classical background. This allows for the description of quantum phenomena in a classical setting, making it useful for applications in cosmology, condensed matter physics, and high energy physics.
In traditional QFT, the background is treated as a fixed, non-dynamical entity. However, in QFT around fixed classical backgrounds, the background is considered to be a dynamical field that interacts with the quantum fields. This allows for a more complete description of quantum phenomena in a classical setting.
Some common examples of classical backgrounds in QFT include gravitational fields, electromagnetic fields, and scalar fields. These backgrounds can be either uniform, such as a constant electric field, or non-uniform, such as a black hole spacetime.
Using QFT around fixed classical backgrounds allows for a more accurate description of quantum phenomena in a classical setting. It also allows for the study of the backreaction of quantum fields on the classical background, which can have important implications in cosmology and other fields of physics.
Current research in QFT around fixed classical backgrounds includes studying the effects of quantum fields on the evolution of the early universe, the behavior of quantum fields in the presence of singularities, and the application of this framework to condensed matter systems, such as superconductors.