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subroutine vvtaxx(ga,gb,tc,g,xm, vertex)
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c This subroutine computes the portion of the amplitude of the four-point
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c coupling of 2 massless color octet gauge bosons
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C with an effective color octect antisymmetric tensor.
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c complex ga(6) : first vector (gluon)
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c complex gb(6) : second vector (gluon)
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c complex tc(18) : tensor current
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c real g : coupling constant
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c complex vertex : amplitude
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c dimension of the current set to arbitrary length
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include "dimension.inc"
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double complex ga(DIM),gb(DIM),tc(DIM)
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double precision xm,xw,g
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double precision sqrTwo
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parameter( sqrTwo=1.41421356237309514547462185873882845044d0 )
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double complex dvertx, vertex
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dvertx = ! + tc( 1)*( ga(1)*gb(1) - ga(1)*gb(1) ) Always zero
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& - tc( 2)*( ga(1)*gb(2) - ga(2)*gb(1) )
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& - tc( 3)*( ga(1)*gb(3) - ga(3)*gb(1) )
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& - tc( 4)*( ga(1)*gb(4) - ga(4)*gb(1) )
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& - tc( 5)*( ga(2)*gb(1) - ga(1)*gb(2) )
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& ! + tc( 6)*( ga(2)*gb(2) - ga(2)*gb(2) ) Always zero
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& + tc( 7)*( ga(2)*gb(3) - ga(3)*gb(2) )
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& + tc( 8)*( ga(2)*gb(4) - ga(4)*gb(2) )
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& - tc( 9)*( ga(3)*gb(1) - ga(1)*gb(3) )
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& + tc(10)*( ga(3)*gb(2) - ga(2)*gb(3) )
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& ! + tc(11)*( ga(3)*gb(3) - ga(3)*gb(3) ) Always zero
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& + tc(12)*( ga(3)*gb(4) - ga(4)*gb(3) )
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& - tc(13)*( ga(4)*gb(1) - ga(1)*gb(4) )
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& + tc(14)*( ga(4)*gb(2) - ga(2)*gb(4) )
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& + tc(15)*( ga(4)*gb(3) - ga(3)*gb(4) )
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& ! + tc(16)*( ga(4)*gb(4) - ga(4)*gb(4) ) Always zero
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vertex = g * dvertx /sqrTwo