Group of invariance of the relativistic four-interval

It is shown that the relativistic four-interval is invariant not only under transformations of the Lorentz group O(1, 3) and the Poincare group P, but also under transformations of the wider group K = PxO(1, 3), which has not yet been described. The symmetry of this group can be realized physically in the description of the kinematics of a radiating or decaying object. The representations of the group K determine the state both of the object itself and of the particles emitted by it, and, in principle, permit the introducion of both external (spin, baryon number) and internal (isospin, hypercharge) variables