RParität

R-parität, also known as R-parity, is a multiplicative quantum number used in supersymmetric theories. It is defined as P_R = (-1)^{3(B-L) + 2s}, where B is baryon number, L is lepton number, and s is spin. The concept was introduced by Farrar and Fayet in 1978 to suppress rapid proton decay in supersymmetric models and to distinguish Standard Model particles from their superpartners.

In models with R-parity conservation, Standard Model particles have R-parity +1 while their superpartners have R-parity -1. This conservation implies that superpartners must be produced in pairs and that the lightest supersymmetric particle (LSP) is stable, since it cannot decay into only Standard Model particles without violating R-parity. If the LSP is neutral and weakly interacting, it provides a natural dark matter candidate and leads to characteristic missing-energy signatures in collider experiments.

R-parity can also be violated, giving rise to R-parity-violating (RPV) models. In such theories, lepton- or baryon-number-violating terms may appear in the superpotential, for example LLE, LQD, or UDD operators. Depending on the strength and structure of the couplings, the LSP may decay into Standard Model particles, reducing missing-energy signals and producing distinctive collider signatures. Proton decay constraints typically require that both baryon- and lepton-number-violating operators are not simultaneously large or that some suppression mechanism is in place.

R-parity thus plays a central role in the phenomenology of supersymmetric theories, influencing collider searches, dark matter implications, and the possible signatures of supersymmetry in experiments.