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**"standard perturbation theory" - what exactly is meant?**

hi,

could someone please help me out with the question in the title, in the following context:

standard perturbation theorycan be viewed as a special case of the

semiclassical method, where one quantises fluctuations around trivial

classical solutions, whereas in soliton or instanton physics, one does the

same thing around non-trivial, non-perturbative classical solutions.

the quantization around trivial classical solutions can be done via the minkowskian path integral, while instanton solutions arise in the euclidean formalism (using a semiclassical approximation, in the sense of stationary phase approximation and steepest descent).

however, i'm not sure what the author (Rajamaran) means with

*standard perturbation theory*and the assertion that instanton solutions are non-perturbative classical solutions.

Thanks a lot.

(i hope my question makes sense, i'm quite new at qm)