Continuous spin particle

In theoretical physics, a continuous spin particle (CSP), sometimes called an infinite spin particle, is a massless particle never observed before in nature. This particle is one of Poincaré group's massless representations which, along with ordinary massless particles, was classified by Eugene Wigner in 1939.^[1] Historically, a compatible theory that could describe this elementary particle was unknown; however, 75 years after Wigner's classification, the first local action principle for bosonic continuous spin particles was introduced in 2014,^[2] and the first local action principle for fermionic continuous spin particles was suggested in 2015.^[3] It has been illustrated that this particle can interact with matter in flat spacetime.^[4][5] Supersymmetric continuous spin gauge theory has been studied in three^[6] and four^[7][8] spacetime dimensions.

In condensed matter systems, CSPs can be understood as massless generalizations of the anyon.^[9]