Chan–Paton factor

Chan–Paton factors are mathematical tools used in string theory and related areas of theoretical physics to label the degrees of freedom associated with open strings. They play a crucial role in ensuring that open strings are correctly incorporated into string theory, particularly in models that include D-branes (which are certain objects in string theory on which open strings can end). In more technical terms, Chan–Paton factors are associated with the endpoints of open strings and provide a way to include gauge symmetry in the theory.