Ramond sector

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In superstring theory, the fermionic field on the closed string may be either periodic or anti-periodic for going around the string. States in the Neveu-Schwarz sector admit one option, while those in the Ramond sector admit the other.

Note that for a fermionic field, the periodicity depends on the coordinates by which the worldsheet is described. In the w-frame, in which the worldsheet of a single string state is described as a long cylinder, states in the Neveu-Schwarz sector are anti-periodic and states in the Ramond sector are periodic. In the z-frame, in which the worldsheet of a single string state is described as an infinite plane, the opposite is correct.

The Neveu-Schwarz sector and Ramond sector are also defined in the open string, according to the boundary conditions of the fermionic field at the edges of the open string.