Relativistic quantum field theory

In theoretical physics, quantum field theory (QFT) is the theoretical framework for constructing quantum mechanical models of subatomic particles in particle physics and quasiparticles in condensed matter physics. It is a set of notions and mathematical tools that combines classical fields, special relativity, and quantum mechanics, and, when combined with the cluster decomposition principle, it may be the only way to do so, while retaining the ideas of quantum point particles and locality. QFT was historically widely believed to be truly fundamental. It is now believed, primarily due to the continued failures of quantization of general relativity, to be only a very good low-energy approximation, i.e. an effective field theory, to some more fundamental theory.

QFT treats particles as excited states of an underlying field, so these are called field quanta. In quantum field theory, quantum mechanical interactions among particles are described by interaction terms among the corresponding underlying quantum fields. These interactions are conveniently visualized by Feynman diagrams, which are a formal tool of relativistically covariant perturbation theory, serving to evaluate particle processes.

Even though QFT is an unavoidable consequence of the reconciliation of quantum mechanics with special relativity (Weinberg (1995)), historically, it emerged in the 1920s with the quantization of the electromagnetic field (the quantization being based on an analogy with the eigenmode expansion of a vibrating string with fixed endpoints).

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