**algebraic quantum field theory** (perturbative, on curved spacetimes, homotopical)

**quantum mechanical system**, **quantum probability**

**interacting field quantization**

In scattering theory the *Møller operator* intertwines the observables of the free theory with those of the interacting theory.

The quantum states $\vert \psi(t)\rangle_I$ in the interaction picture of quantum mechanics are by definition (this equation) related to the asymptotic free states $\vert\psi\rangle$ by

$\vert \psi(t)\rangle_I
\;=\;
\exp\left({\tfrac{- t}{i \hbar} H_{free}}\right)
\exp\left({\tfrac{t}{i \hbar} H_{free} + \tfrac{t}{i \hbar} V} \right)
\vert \psi \rangle$

and conversely

$\vert \psi \rangle
\;=\;
\underbrace{
\exp\left({\tfrac{- t}{i \hbar} H_{free} + \tfrac{t}{i \hbar} V} \right)
\exp\left({\tfrac{+ t}{i \hbar} H_{free}}\right)
}
\vert \psi(t)\rangle_I$

the suitable limit for $t \to \mp \infty$ of the operator under the brace is called the *Møller operator*

$\Omega{\pm}
\;\coloneqq\;
\underset{t \to \mp \infty}{\lim}
\exp\left({\tfrac{- t}{i \hbar} H_{free} + \tfrac{t}{i \hbar} V} \right)
\exp\left({\tfrac{+ t}{i \hbar} H_{free}}\right)$

(e.g. BEM 01)

In perturbative quantum field theory the maps that intertwine the Wick algebra of quantum observables of the free field theory with the interacting field algebra are, on regular polynomial observables. the derivatives of the Bogoliubov formula of the given S-matrix $\mathcal{S}$ for the given interaction $S_{int}$ with respect to source fields:

$\mathcal{R}(-)
\;\coloneqq\;
\mathcal{S}(S_{int})^{-1}
\star_H
(\mathcal{S}(S_{int}) \star_F (-))$

(Here $\star_H$ denotes the star product induced by the Wightman propagator, hence the Wick algebra-product, while $\star_F$ denotes the star product induced by the Feynman propagator, hence the time-ordered product. The inverse $(-)^{-1}$ is taken with respect to $\star_H$.)

This $\mathcal{R}(-)$ is referred to as the *quantum Møller operator* in (Hawkins-Rejzner 16, below def. 5.1). (But notice that in many previous articles in perturbative AQFT, by the same authors and by others, the very same operator is referred to just as the “intertwining operator”, or similar.)

Discussion in quantum mechanics:

- A. Baute, I. Egusquiza, J. Muga,
*Møller operators and Lippmann-Schwinger equations for step-like potentials*(arXiv:quant-ph/0104043)

Discussion in relativistic perturbative quantum field theory in the rigorous formulation of causal perturbation theory/perturbative AQFT:

- Eli Hawkins, Kasia Rejzner,
*The Star Product in Interacting Quantum Field Theory*(arXiv:1612.09157)

Last revised on October 8, 2019 at 09:47:45. See the history of this page for a list of all contributions to it.