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HELAS/iovgox.f
 
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      subroutine iovgox(fi,fo,vc,gc , vertex)
 
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c
 
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c This subroutine computes an amplitude of the fermion-fermion-vector
 
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c coupling in the case when they are all color octets.
 
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c
 
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c input:
 
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c       complex fi(6)          : flow-in  fermion                   |fi>
 
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c       complex fo(6)          : flow-out fermion                   <fo|
 
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c       complex vc(6)          : input    vector                      v
 
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c       complex gc(2)          : coupling constants                  gvf
 
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c
 
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c output:
 
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c       complex vertex         : amplitude                     <fo|v|fi>
 
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c     
 
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      implicit none
 
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      double complex fi(6),fo(6),gc(2),vc(6),vertex
 
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      double precision rZero, rOne
 
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      parameter( rZero = 0.0d0 )
 
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      double complex cImag, cZero
 
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      parameter( cImag = ( 0.0d0, 1.0d0 ), cZero = ( 0.0d0, 0.0d0 ) )
 
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      vertex =  gc(1)*( (fo(3)*fi(1)+fo(4)*fi(2))*vc(1)
 
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     &                 +(fo(3)*fi(2)+fo(4)*fi(1))*vc(2)
 
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     &                 -(fo(3)*fi(2)-fo(4)*fi(1))*vc(3)*cImag
 
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     &                 +(fo(3)*fi(1)-fo(4)*fi(2))*vc(4)        )
 
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      if ( gc(2).ne.cZero ) then
 
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         vertex = vertex
 
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     &          + gc(2)*( (fo(1)*fi(3)+fo(2)*fi(4))*vc(1)
 
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     &                   -(fo(1)*fi(4)+fo(2)*fi(3))*vc(2)
 
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     &                   +(fo(1)*fi(4)-fo(2)*fi(3))*vc(3)*cImag
 
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     &                   -(fo(1)*fi(3)-fo(2)*fi(4))*vc(4)        )
 
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      end if
 
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c
 
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      return
 
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      end