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Dynamical NNLO parton distributions

Utilizing recent DIS measurements (σ_r, F_{2,3,L}) and data on hadronic dilepton production we determine at NNLO (3-loop) of QCD the dynamical parton distributions of the nucleon generated radiatively from valencelike positive input distributions at an optimally chosen low resolution scale (Q_0^2 < 1 GeV^2). These are compared with `standard&#39; NNLO distributions generated from positive input distributions at some fixed and higher resolution scale (Q_0^2 > 1 GeV^2). Although the NNLO corrections imply in both approaches an improved value of χ^2, typically χ^2_{NNLO} \simeq 0.9 χ^2_{NLO}, present DIS data are still not sufficiently accurate to distinguish between NLO results and the minute NNLO effects of a few percent, despite of the fact that the dynamical NNLO uncertainties are somewhat smaller than the NLO ones and both are, as expected, smaller than those of their `standard&#39; counterparts. The dynamical predictions for F_L(x,Q^2) become perturbatively stable already at Q^2 = 2-3 GeV^2 where precision measurements could even delineate NNLO effects in the very small-x region. This is in contrast to the common `standard&#39; approach but NNLO/NLO differences are here less distinguishable due to the much larger 1σuncertainty bands. Within the dynamical approach we obtain α_s(M_Z^2)=0.1124 \pm 0.0020, whereas the somewhat less constrained `standard&#39; fit gives α_s(M_Z^2)=0.1158 \pm 0.0035.