Abstract :
We present consistently ordered calculations of the structure functions F2 (x, Q2) and FL (x, Q2) in different expansion schemes. After discussing the standard expansion in powers of αS(Q2) we consider a leading-order expansion in ln(1x) and finally an expansion which is leading order in both ln(1x) and αS(Q2), and which is the only really correct expansion scheme. Ordering the calculation in a renormalization-scheme-consistent manner, there is no factorization scheme dependence, and the calculational method naturally includes to the “physical anomalous dimensions” of Catani. However, it imposes stronger constraints than just the use of these effective anomalous dimensions. A relationship between the small-x forms of the inputs F2(x,QI2) and FL (x, QI2) is predicted. Analysis of a wide range of data for F2 (x, Q2) is performed, and a very good global fit obtained, particularly for data at small x. The fit allows a prediction for FL (x, Q2) to be produced, which is smaller than those produced by the usual NLO-in-αS(Q2) fits to F2(x, Q2) and different in shape.
