! $Id: xa2hgp.f90,v 1.1 2002/03/06 17:12:12 gsalam Exp $ ! Automatically generated from f77 file, with addition of "d0" ! From avogt@nikhef.nl Thu Feb 7 15:34:35 2002 ! Date: Wed, 6 Feb 2002 18:23:05 +0100 (MET) ! From: Andreas Vogt ! To: G. Salam ! Cc: A. Vogt ! Subject: the subroutine ! ! ! ..File: xa2hgp.f ! ! ! ..Calculation of the alpha_s^2 heavy-quark singlet operator matrix ! element (OME) a^2_Hg(x) in the MS(bar) scheme for mu_f = m_H via ! a compact parametrization involving only logarithms. ! The coupling constant is normalized as a_s = alpha_s/(4*pi). ! ! ..This quantity, presented in Appendix B of M. Buza, Y. Matiounine, ! J. Smith and W.L. van Neerven, Eur. Phys. J. C1 (1998) 301 (BSMN), ! is required for the N_f matching of the NNLO parton densities. ! ! ..The distributions (in the mathematical sense) are given as in eq. ! (B.26) of Floratos, Kounnas, Lacaze: Nucl. Phys. B192 (1981) 417. ! The name-endings A, B, and C of the functions below correspond to ! the kernel superscripts [2], [3], and [1] in that equation. ! ! ..The relative accuracy of the OME, as well as of its convolutions ! with gluon distributions, amounts to a few thousandth. ! ! ..Reference: not yet known ! hep-ph/yymmnnn ! ..The user should also cite the original calculation by BSMN. ! ! ! ===================================================================== ! ! ! ..This is the regular piece. ! FUNCTION A2HGA (Y) IMPLICIT REAL*8 (A-Z) ! DL = LOG (Y) DL1 = LOG (1.-Y) ! A2HGA = - 24.89d0 / Y - 187.8d0 + 249.6d0 * Y - 146.8d0 * DL**2 * DL1 & & - 1.556d0 * DL**3 - 3.292d0 * DL**2 - 93.68d0 * DL & & - 1.111d0 * DL1**3 - 0.400d0 * DL1**2 - 2.770d0 * DL1 ! RETURN END ! ! --------------------------------------------------------------------- ! ! ! ..This is the 'local' piece, which has no counterpart in W. van ! Neerven's program, as it does not exist in the exact expressions. ! FUNCTION A2HGC (Y) IMPLICIT REAL*8 (A-Z) ! A2HGC = - 0.006d0 ! RETURN END