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wwwwxx.F
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subroutine wwwwxx(wm1,wp1,wm2,wp2,gwwa,gwwz , vertex)
c
c This subroutine computes an amplitude of the four-point W-/W+ coupling.
c
c input:
c complex wm1(0:3) : first flow-out W- wm1
c complex wp1(0:3) : first flow-out W+ wp1
c complex wm2(0:3) : second flow-out W- wm2
c complex wp2(0:3) : second flow-out W+ wp2
c *** WK: The vertex factor (HELAS) was gwwa**2+gwwz**2
c *** For WHIZARD, this is replaced by gwwa, so this parameter is
c *** understood as the 4W coupling. gwwz is ignored.
c real gwwa : coupling constant of W and A gwwa
c real gwwz : coupling constant of W and Z gwwz
c real zmass : mass of Z
c real zwidth : width of Z
c
c output:
c complex vertex : amplitude gamma(wm1,wp1,wm2,wp2)
c
implicit none
double complex wm1(6),wp1(6),wm2(6),wp2(6),vertex
double complex dv1(0:3),dv2(0:3),dv3(0:3),dv4(0:3),dvertx
double complex v12,v13,v14,v23,v24,v34
double precision pwm1(0:3),pwp1(0:3),pwm2(0:3),pwp2(0:3)
double precision gwwa,gwwz
double precision rZero, rOne, rTwo
parameter( rZero = 0.0d0, rOne = 1.0d0, rTwo = 2.0d0 )
#ifdef HELAS_CHECK
double precision pm
double precision epsi
parameter( epsi = 2.0d-5 )
integer stdo
parameter( stdo = 6 )
#endif
c
pwm1(0) = dble( wm1(5))
pwm1(1) = dble( wm1(6))
pwm1(2) = dimag(wm1(6))
pwm1(3) = dimag(wm1(5))
pwp1(0) = dble( wp1(5))
pwp1(1) = dble( wp1(6))
pwp1(2) = dimag(wp1(6))
pwp1(3) = dimag(wp1(5))
pwm2(0) = dble( wm2(5))
pwm2(1) = dble( wm2(6))
pwm2(2) = dimag(wm2(6))
pwm2(3) = dimag(wm2(5))
pwp2(0) = dble( wp2(5))
pwp2(1) = dble( wp2(6))
pwp2(2) = dimag(wp2(6))
pwp2(3) = dimag(wp2(5))
#ifdef HELAS_CHECK
if ( abs(wm1(1))+abs(wm1(2))
& +abs(wm1(3))+abs(wm1(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : wm1 in wwwwxx is zero vector'
endif
if ( abs(wm1(5))+abs(wm1(5)).eq.rZero ) then
write(stdo,*)
& ' helas-error : wm1 in wwwwxx has zero momentum'
endif
if ( abs(wp1(1))+abs(wp1(2))
& +abs(wp1(3))+abs(wp1(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : wp1 in wwwwxx is zero vector'
endif
if ( abs(wp1(5))+abs(wp1(5)).eq.rZero ) then
write(stdo,*)
& ' helas-error : wp1 in wwwwxx has zero momentum'
endif
if ( abs(wm2(1))+abs(wm2(2))
& +abs(wm2(3))+abs(wm2(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : wm2 in wwwwxx is zero vector'
endif
if ( abs(wm2(5))+abs(wm2(5)).eq.rZero ) then
write(stdo,*)
& ' helas-error : wm2 in wwwwxx has zero momentum'
endif
if ( abs(wp2(1))+abs(wp2(2))
& +abs(wp2(3))+abs(wp2(4)).eq.rZero ) then
write(stdo,*) ' helas-warn : wp2 in wwwwxx is zero vector'
endif
if ( abs(wp2(5))+abs(wp2(5)).eq.rZero ) then
write(stdo,*)
& ' helas-error : wp2 in wwwwxx has zero momentum'
endif
pm = max( abs(pwm1(0)),abs(pwp1(0)),abs(pwm2(0)),abs(pwp2(0)),
& abs(pwm1(1)),abs(pwp1(1)),abs(pwm2(1)),abs(pwp2(1)),
& abs(pwm1(2)),abs(pwp1(2)),abs(pwm2(2)),abs(pwp2(2)),
& abs(pwm1(3)),abs(pwp1(3)),abs(pwm2(3)),abs(pwp2(3)) )
if ( abs(wm1(5)+wp1(5)+wm2(5)+wp2(5))
& +abs(wm1(6)+wp1(6)+wm2(6)+wp2(6)).ge.pm*epsi ) then
write(stdo,*)
& ' helas-error : wm1,wp1,wm2,wp2 in wwwwxx'
write(stdo,*)
& ' : have not balanced momenta'
endif
if ( gwwa.eq.rZero ) then
write(stdo,*) ' helas-error : gwwa in wwwwxx is zero coupling'
endif
if ( gwwz.eq.rZero ) then
write(stdo,*)
& ' helas-error : gwwz in wwwwxx is zero coupling'
endif
if ( gwwa.lt.rZero .or. gwwa.ge.gwwz ) then
write(stdo,*)
& ' helas-warn : gwwa/gwwz in wwwwxx are non-standard couplings'
write(stdo,*)
& ' : gwwa = ',gwwa,' gwwz = ',gwwz
endif
#endif
dv1(0) = dcmplx(wm1(1))
dv1(1) = dcmplx(wm1(2))
dv1(2) = dcmplx(wm1(3))
dv1(3) = dcmplx(wm1(4))
dv2(0) = dcmplx(wp1(1))
dv2(1) = dcmplx(wp1(2))
dv2(2) = dcmplx(wp1(3))
dv2(3) = dcmplx(wp1(4))
dv3(0) = dcmplx(wm2(1))
dv3(1) = dcmplx(wm2(2))
dv3(2) = dcmplx(wm2(3))
dv3(3) = dcmplx(wm2(4))
dv4(0) = dcmplx(wp2(1))
dv4(1) = dcmplx(wp2(2))
dv4(2) = dcmplx(wp2(3))
dv4(3) = dcmplx(wp2(4))
v12 = dv1(0)*dv2(0)-dv1(1)*dv2(1)-dv1(2)*dv2(2)-dv1(3)*dv2(3)
v13 = dv1(0)*dv3(0)-dv1(1)*dv3(1)-dv1(2)*dv3(2)-dv1(3)*dv3(3)
v14 = dv1(0)*dv4(0)-dv1(1)*dv4(1)-dv1(2)*dv4(2)-dv1(3)*dv4(3)
v23 = dv2(0)*dv3(0)-dv2(1)*dv3(1)-dv2(2)*dv3(2)-dv2(3)*dv3(3)
v24 = dv2(0)*dv4(0)-dv2(1)*dv4(1)-dv2(2)*dv4(2)-dv2(3)*dv4(3)
v34 = dv3(0)*dv4(0)-dv3(1)*dv4(1)-dv3(2)*dv4(2)-dv3(3)*dv4(3)
c *** WK: This is replaced:
c dvertx = (v12*v34 + v14*v23 - rTwo*v13*v24)*(gwwa**2+gwwz**2)
dvertx = (v12*v34 + v14*v23 - rTwo*v13*v24)*gwwa
vertex = -dcmplx( dvertx )
c
return
end

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