THRESHOLD EFFECTS IN THREE-BODY KINEMATICS

J. Fiol$^\ast$, R. O. Barrachina$^\ast$ and V. D. Rodr\'{\i}guez$^\sharp$

$^\ast$Centro At\'omico Bariloche and Instituto Balseiro, 8400 S. C. de
Bariloche, R\'{\i}o Negro, Argentina 
$^\sharp$Departamento de F\'{\i}sica, Universidad de Buenos Aires, FCEyN, 
1428 Buenos Aires, Argentina

We show how the single-particles' double differential cross sections (DDCS)
in breakup collisions  are  intertwined  by  the dynamical constraints.  In
particular, we study the  corresponding  relations among threshold and cusp
structures and identify some of  their  general  properties  by  means of a
final-state  interaction theory.  Finally, we  show  how  these  structures
change with the relative mass ratios of  the  three  particles in the final
state.