In theoretical physics orientifold is a generalization of the notion of orbifold, proposed by Augusto Sagnotti in 1987. The novelty is that in the case of string theory the non-trivial element(s) of the orbifold group includes the reversal of the orientation of the string. Orientifolding therefore produces unoriented strings—strings that carry no "arrow" and whose two opposite orientations are equivalent. Type I string theory is the simplest example of such a theory and can be obtained by orientifolding type IIB string theory.
In mathematical terms, given a smooth manifold , two discrete, freely acting, groups and and the worldsheet parity operator (such that ) an orientifold is expressed as the quotient space . If is empty, then the quotient space is an orbifold. If is not empty, then it is an orientifold.
In theoretical physics orientifold is a generalization of the notion of orbifold, proposed by Augusto Sagnotti in 1987. The novelty is that in the case...
Augusto Sagnotti in 1988, the type I string theory can be obtained as an orientifold of type IIB string theory, with 32 half-D9-branes added in the vacuum...
theory with the coupling 1/g. This equivalence is known as S-duality. Orientifold of type IIB string theory leads to type I string theory. The mathematical...
important contributions to string theory (most notably the discovery of the orientifold, which connects type I string theory to type IIB string theory). Giovanni...
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