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subroutine sssxxx(s1,s2,s3,gc , vertex)
c
c This subroutine computes an amplitude of the three-scalar coupling.
c
c input:
c complex s1(3) : first scalar s1
c complex s2(3) : second scalar s2
c complex s3(3) : third scalar s3
c complex gc : coupling constant ghhh
c
c output:
c complex vertex : amplitude gamma(s1,s2,s3)
c
implicit none
double complex s1(3),s2(3),s3(3),gc,vertex
#ifdef HELAS_CHECK
double precision p0,p1,p2,p3,q0,q1,q2,q3,r0,r1,r2,r3,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
p0 = dble( s1(2))
p1 = dble( s1(3))
p2 = dimag(s1(3))
p3 = dimag(s1(2))
q0 = dble( s2(2))
q1 = dble( s2(3))
q2 = dimag(s2(3))
q3 = dimag(s2(2))
r0 = dble( s3(2))
r1 = dble( s3(3))
r2 = dimag(s3(3))
r3 = dimag(s3(2))
if ( s1(1).eq.cZero ) then
write(stdo,*) ' helas-warn : s1 in sssxxx is zero scalar'
endif
if ( abs(s1(2))+abs(s1(3)).eq.rZero ) then
write(stdo,*)
& ' helas-error : s1 in sssxxx has zero momentum'
endif
if ( s2(1).eq.cZero ) then
write(stdo,*) ' helas-warn : s2 in sssxxx is zero scalar'
endif
if ( abs(s2(2))+abs(s2(3)).eq.rZero ) then
write(stdo,*)
& ' helas-error : s2 in sssxxx has zero momentum'
endif
if ( s3(1).eq.cZero ) then
write(stdo,*) ' helas-warn : s3 in sssxxx is zero scalar'
endif
if ( abs(s3(2))+abs(s3(3)).eq.rZero ) then
write(stdo,*)
& ' helas-error : s3 in sssxxx has zero momentum'
endif
pm = max( abs(p0),abs(q0),abs(r0),abs(p1),abs(q1),abs(r1),
& abs(p2),abs(q2),abs(r2),abs(p3),abs(q3),abs(r3) )
if ( abs(s1(2)+s2(2)+s3(2))+abs(s1(3)+s2(3)+s3(3))
& .ge.pm*epsi ) then
write(stdo,*)
& ' helas-error : s1,s2,s3 in sssxxx'
write(stdo,*)
& ' : have not balanced momenta'
endif
if ( gc.eq.cZero ) then
write(stdo,*)
& ' helas-error : gc in sssxxx is zero coupling'
endif
#endif
vertex = gc*s1(1)*s2(1)*s3(1)
c
return
end
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