Definition of "orientifolds" [orientifolds]

• Plural form of orientifold. (noun)

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• "For example, one of the simplest ways around the old “no go” arguments for de Sitter space is to take into account the positive term in the moduli potential that arises in supercritical dimensionality (combined with other ingredients such as orientifolds and RR fluxes)."
• "There was a no-go theorem (Maldacena-Nunez) showing that starting with higher dimensional theory, one cannot obtain deSitter vacua without invoking elements unique to string theory (e.g orientifolds)."
• "F-theoretical flux vacua i.e. type IIB vacua with non-trivial axion-dilaton fields, orientifolds, and D-branes."