  The collision of two massless, gravitationally interacting, point-like
massless particles, boosted to the speed of light, colliding with an impact
parameter b is being investigated. The collision takes place in four space-time
flat dimensional background. A perturbative scheme is employed and the
corrections to the energy momentum tensor and to the metric are computed and
closed form formulas are provided. This includes the back-reaction on the
metric after the collision. Including such corrections suggests that the
tracelessness of the initial stress tensors of the colliding particles is
preserved during and after the collision. The necessity for introducing an
impact parameter in the perturbative treatment is highlighted and the breaking
of the underlying perturbative approach at b = 0 is motivated. In addition, the
energy radiated in the form of gravitational bremsstrahlung radiation is
discussed while an example from gravitational-waves collision is being studied.
