Anharmonic oscillator is considered using an unusual, logarithmic form of the anharmonicity. The model is shown connected with the more conventional power-law anharmonicity [Formula: see text] in the limit [Formula: see text]. An efficient and user-friendly method of the solution of the model is found in the large-N expansion technique.
Magnetic impurities at quantum critical points: Large-
N
expansion and connections to symmetry-protected topological states