Polarized structure functions

The spin structure function g₁(x, Q²) and the related longitudinally polarized parton densities are discussed in LO and NLO QCD for different factorization schemes within the common 'standard' scenario of polarized parton distributing functions (pdfs) with a flavour-symmetric light sea (antiquark) distribution δ and a completely SU(3)_f broken 'valence' scenario with totally flavour–asymmetric light sea densities (δū ≠ δ ≠ δ). The latter flavour-broken light sea densities are modelled with the help of a Pauli-blocking ansatz which complies with predictions of the chiral quark–soliton model and expectations based on the statistical parton model as well as with the corresponding, well established, flavour-broken unpolarized sea ( > ū). Various parametrizations of polarized pdfs and results of recent analyses are discussed and compared, with particular emphasis on their implications at small x and for the polarized gluon distributions δg(x, Q²). Further (future) direct measurements of δū and δ are discussed and suggested, such as polarized semi–inclusive DIS production processes of charged hadrons, polarized Drell–Yan (γ*) dilepton production processes for future longitudinally polarized and collision experiments, and the production of weak vector bosons (W^±, Z⁰) via singly and doubly longitudinally polarized pp and pn collisions.