In this type of potential, the four-vector probability current simply equals two times the four- momentum.
In this type of potential, the four-vector probability current simply equals two times the four- momentum. In natural units, the normalization factor for the relativistic solutions of this type of potential equals the square root of energy plus mass. This potential is characterized by a doubly- degenerate continuous energy spectrum ranging from zero to positive infinity. The Hamiltonian for this potential was written as alpha dotted with the momentum plus beta times the mass by Paul Dirac. This potential's solutions can be written as a sum of two plane waves traveling in opposite directions, but since that solution is not normalizable, a Fourier transform can be introduced to write the solution as a wave packet. This system is conceptually equivalent to a particle-in-a-box with an infinite box length. For 10 points, name this quantum system consisting of a particle in a region with zero potential energy.
In this type of potential, the four-vector probability current simply equals two times the four- momentum.
free particle [or zero potential before the word ―zero‖ in the giveaway is read, accept answers expressing that ―there is  no potential‖;  prompt on ―spin 1/2  particle‖ or ―fermion‖ or ―spin plus Â½ particle‖ or ―spin minus Â½ particle‖]