Figure 2. Initial position of the CM when the velocity of the CM
v
and the Spin
S
cm
=
S
direction form an angle α. It is perpendicular to the vectors
v
and
*
u
0
×
*
r
0
, of distance to the center O −CM = (v/2) sin α, in natural units, and is independent of the initial position and velocity of the CC.
In general, the separation between both centers CC and CM, is in the interval |
r
−
q
| ∈ [1/2 −(v/2) sin α, 1/2 + (v/2) sin α] in natural units, so that this separation is not a constant of the motion.In general, the initial position of the CM for the laboratory observer
q
0
, given in (18), is contained in the zitterbewegung plane (with d = 0 = b), is independent of the initial position of the CC,
*
r
0
, and is depicted in the figure 2. The distance to the center is (v/2) sin α. If
v
is perpendicular to the zitterbewegung plane,
v
·
*
r
0
=
v
·
*
u
0
= 0, and the CM is at the center of the circle and becomes equidistant of the trajectory of the CC. If
v
, has a different orientation, the separation between both centers CC and CM, |
r
−
q
|, is not a constant of the motion. It is in the range |
r
−
q
| ∈ [
R
0
−(v/2) sin α,
R
0
+(v/2) sin α] in natural units.We must remark that the CC
r
0
is the Poincaré transformed of the point
*
r
0
, but
q
0
is NOT the Poincaré transformed of the CM
*
q
0
in
*
O
. It is the CM of the particle in the laboratory frame O, at the same time
t
0
than
r
0
, while
*
r
0
and
*
q
0
are considered simultaneous at the frame
*
O
. Simultaneous events in one frame are not simultaneous in another. The point
q
0
represents the location of the CM of the particle simultaneous with
r
0
, for the laboratory observer.

8. Poincaré invariant interaction boundary conditions


9. Poincaré interaction examples

We will now represent different interactions with different initial boundary conditions: