Spin in quantum physics: general theory and application on ‘The Proton Spin Crisis’

The theoretical framework for small scale phenomena is quantum physics, where the word “quantum” refers to the smallest possible package of a physical quantity. Especially, in this thesis, we consider the spin of elementary particles, a kind of “intrinsic” angular momentum. This property is peculiar to quantum theories and we first discuss how it is connected to non- relativistic low energy processes. In this approach the spin is not automatically contained in the theory. It is rather experimental evidence, such as the Stern-Gerlach experiment, which shows that spin must be introduced to fully explain all observations. We also look at the connection to spin in relativistic high energy theories. This requires a knowledge of the Poincar√© group, as this group determines the structure of space-time to a large extent.

We also discuss the article by E. Wigner from 1939, where he classified the little group connected to the inhomogeneous Lorentz group, and all its fundamental representations. This allowed Wigner to classify fundamental particles according to their masses and spins. Spin is revealed to result from the symmetries of space-time.

Author: Turk, Christian

Source: Luleå University of Technology

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