pygdir.f

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C*********************************************************************
 
C...PYGDIR
C...Evaluates the direct contribution, i.e. the C^gamma term,
C...as needed in MSbar parametrizations.
C...Adapted from SaSgam library, authors G.A. Schuler and T. Sjostrand.
 
      SUBROUTINE pygdir(X,Q2,P2,Q02,XPGA)
 
C...Double precision and integer declarations.
      IMPLICIT DOUBLE PRECISION(a-h, o-z)
      IMPLICIT INTEGER(i-n)
      INTEGER pyk,pychge,pycomp
C...Local array and data.
      dimension xpga(-6:6)
      DATA pmc/1.3d0/, pmb/4.6d0/, aem2pi/0.0011614d0/
 
C...Reset output.
      DO 100 kfl=-6,6
        xpga(kfl)=0d0
  100 CONTINUE
 
C...Evaluate common x-dependent expression.
      xtmp = (x**2+(1d0-x)**2) * (-log(x)) - 1d0
      cgam = 3d0*aem2pi*x * (xtmp*(1d0+p2/(p2+q02)) + 6d0*x*(1d0-x))
 
C...d, u, s part by simple charge factor.
      xpga(1)=(1d0/9d0)*cgam
      xpga(2)=(4d0/9d0)*cgam
      xpga(3)=(1d0/9d0)*cgam
 
C...Also fill for antiquarks.
      DO 110 kf=1,5
        xpga(-kf)=xpga(kf)
  110 CONTINUE
 
      RETURN
      END