Direct solution of renormalization group equations of QCD in x-space: NLO implementations at leading twist

Abstract

We illustrate the implementation of a method based on the use of recursion relations in (Bjorken) x-space for the solution of the evolution equations of QCD for all the leading twist distributions. The algorithm has the advantage of being very fast. The implementation that we release is written in C and is performed to next-to-leading order in α s . Program summary Title of program: evolution.c Catalogue identifier: ADUB Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADUB Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: Athlon 1800 plus Operating system under which the program has been tested: Linux Programming language used: C Peripherals used: Laser printer No. of bytes in distributed program, including test data, etc.: 4559 No. of lines in distributed program, including test data, etc.: 1048 Distribution format: gzip file Nature of physical problem: The program provided here solves the DGLAP evolution equations to next-to-leading order α s , for unpolarized, longitudinally polarized and transversely polarized parton distributions. Method of solution: We use a recursive method based on an expansion of the solution in powers of log( α s ( Q)/ α s ( Q 0)). Typical running time: About 1 minute and 30 seconds for the unpolarized and longitudinally polarized cases and 1 minute for the transversely polarized case.