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subroutine vvsxxx(v1,v2,sc,gc , vertex)
c
c This subroutine computes an amplitude of the vector-vector-scalar
c coupling.
c
c input:
c complex v1(6) : first vector v1
c complex v2(6) : second vector v2
c complex sc(3) : input scalar s
c complex gc : coupling constant gvvh
c
c output:
c complex vertex : amplitude gamma(v1,v2,s)
c
implicit none
double complex v1(6),v2(6),sc(3),gc,vertex
#ifdef HELAS_CHECK
double precision p10,p11,p12,p13,p20,p21,p22,p23,q0,q1,q2,q3,pm
double precision epsi
parameter( epsi = 4.0d-5 )
double precision rZero
parameter( rZero = 0.0d0 )
double complex cZero
parameter( cZero = ( 0.0d0, 0.0d0 ) )
integer stdo
parameter( stdo = 6 )
#endif
c
#ifdef HELAS_CHECK
p10 = dble( v1(5))
p11 = dble( v1(6))
p12 = dimag(v1(6))
p13 = dimag(v1(5))
p20 = dble( v2(5))
p21 = dble( v2(6))
p22 = dimag(v2(6))
p23 = dimag(v2(5))
q0 = dble( sc(2))
q1 = dble( sc(3))
q2 = dimag(sc(3))
q3 = dimag(sc(2))
if ( abs(v1(1))+abs(v1(2))+abs(v1(3))+abs(v1(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : v1 in vvsxxx is zero vector'
endif
if ( abs(v1(5))+abs(v1(6)).eq.rZero ) then
write(stdo,*)
& ' helas-error : v1 in vvsxxx has zero momentum'
endif
if ( abs(v2(1))+abs(v2(2))+abs(v2(3))+abs(v2(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : v2 in vvsxxx is zero vector'
endif
if ( abs(v2(5))+abs(v2(6)).eq.rZero ) then
write(stdo,*)
& ' helas-error : v2 in vvsxxx has zero momentum'
endif
if ( abs(sc(1)).eq.rZero) then
write(stdo,*) ' helas-warn : sc in vvsxxx is zero scalar'
endif
if ( abs(sc(2))+abs(sc(3)).eq.rZero ) then
write(stdo,*)
& ' helas-error : sc in vvsxxx has zero momentum'
endif
pm = max( abs(p10),abs(p20),abs(q0),abs(p11),abs(p21),abs(q1),
& abs(p12),abs(p22),abs(q2),abs(p13),abs(p23),abs(q3) )
if ( abs(v1(5)+v2(5)+sc(2))+abs(v1(6)+v2(6)+sc(3))
& .ge.pm*epsi ) then
write(stdo,*)
& ' helas-error : v1,v2,sc in vvsxxx'
write(stdo,*)
& ' : have not balanced momenta'
endif
if (gc.eq.cZero) then
write(stdo,*) ' helas-error : gc in vvsxxx is zero coupling'
endif
#endif
vertex = gc*sc(1)
& *(v1(1)*v2(1)-v1(2)*v2(2)-v1(3)*v2(3)-v1(4)*v2(4))
c
return
end
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