2016/07/19 by Cheng-Yang Lee, Lee, Cheng-Yang
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Theory (hep-th) #Quantum, superfluid, helium dynamics #hep-th
paper · pdf · doi:10.48550/arxiv.1607.05370
References added. Typos and claims are corrected. 4 pages, no figures
openalex publication_date 2016/07/19 · arxiv created 2016/09/07 · arxiv updated 2016/09/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
It is a well-known fact that helicity is a Lorentz-invariant for massless but not for massive particles. Nevertheless, a satisfactory proof of this fact and a detailed analysis on the relative orientation between spin and the momentum are not readily available. One such analysis was presented by Wigner where a formula for the angle between the spin and the momentum is derived for massive particle states undergoing two successive boosts in orthogonal directions. In this note, using the Wigner rotation, an alternative derivation is provided.