Gerasimov-Drell-Hearn and Burkhardt-Cottingham Sum Rules for Proton, Neutron and Deuteron

A description of the generalized Gerasimov-Drell-Hearn sum rules for proton, neutron and deuteron is suggested. The proton consideration confirms the earlier conjecture, that the structure function $g_T$ features a smooth $Q^2-$dependence, while the structure function $g_2$ is changing rapidly, due to the elastic contribution to the Burkhardt-Cottingham sum rule. The neutron case features the close connection to the Bjorken sum rule. The deuteron case reveals the crucial role of photodesintegration channel, resulting in the strong nuclear correction at very low $Q^2$. The new approximate sum rules for this channel reflecting the delicate interplay between nucleon and nuclear structure are suggested.