Review of JLab and Mainz experimental results for spin-independent generalized nucleon polarizabilities

The nucleon polarizabilities are fundamental properties that characterize the system's response to an external electromagnetic (EM) field. They describe how easily the charge and magnetization distributions inside the system are distorted by the EM field, such as during the Compton scattering with a real photon. When the polarizabilities are generalized to finite momentum transfer by replacing the incoming real photon of the Compton scattering process with a space-like virtual photon, they map out the deformation of the quark densities in a proton subject to an EM field. They shed light to the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds quarks and gluons together. Recent experimental measurements at Jefferson Lab have provided high precision data, that offer guidance, but at the same time present significant challenges to the nuclear theory. Future experimental programs are currently ongoing, and they will advance further the study of the generalized polarizabilities, both in terms of the kinematic range as well as on the level of the experimental precision.