Nucleon Spin Sum Rules and Spin Polarizabilities at low Q^2

We report on recently published experimental studies on spin sum rules, namely the generalized Gerasimov-Drell-Hearn, Bjorken, Burkhardt-Cottingham, Schwinger, and generalized spin polarizability sum rules. The data were taken at Jefferson Lab in Halls A and B by experiments E97-110 and EG4, respectively. They covered the very low Q^2 domain, down to Q^2≃0.02 GeV^2, where Chiral Effective Field Theory (χEFT) predictions should be valid. While some of the obervables agree with the state-of-the-art χEFT predictions, others are in tensions, including the Longitudinal-Transverse interference polarizability δ_ LT^n(Q^2) for which χEFT prediction was expected to be robust. This suggests that χEFT does not yet consistently describes nucleon spin observables, even in the very low Q^2 domain covered by the experiments.