In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact...

In quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated...

Møller–Plesset perturbation theory (MP) is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...

cosmological perturbation theory is the theory by which the evolution of structure is understood in the Big Bang model. Cosmological perturbation theory may be...

Chiral perturbation theory (ChPT) is an effective field theory constructed with a Lagrangian consistent with the (approximate) chiral symmetry of quantum...

represented by a Feynman diagram according to perturbation theory in quantum mechanics. Quantum field theory emerged from the work of generations of theoretical...

without derivatives. This means that one can manage this theory only by perturbation theory with small nonlinearities.[citation needed] Note that the...

In mathematics, a singular perturbation problem is a problem containing a small parameter that cannot be approximated by setting the parameter value to...

straightforwardly defined using the techniques of perturbation theory, but it is not known in general how to define string theory nonperturbatively. It is also not clear...

In mathematics, variational perturbation theory (VPT) is a mathematical method to convert divergent power series in a small expansion parameter, say s...