Abstract
We analyse the problem of assigning sign choices to O-planes in orientifolds of type II string theory. We show that there exists a sequence of invariant p-gerbes with \(p\ge -1\), which give rise to sign choices and are related by coboundary maps. We prove that the sign choice homomorphisms stabilise with the dimension of the orientifold and we derive topological constraints on the possible sign configurations. Concrete calculations for spherical and toroidal orientifolds are carried out, and in particular we exhibit a four-dimensional orientifold where not every sign choice is geometrically attainable. We elucidate how the K-theory groups associated with invariant p-gerbes for \(p=-1,0,1\) interact with the coboundary maps. This allows us to interpret a notion of K-theory due to Gao and Hori as a special case of twisted \(KR\)-theory, which consequently implies the homotopy invariance and Fredholm module description of their construction.
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Notes
This seems to be at odds with the result of [7] who used \(C^*\)-algebra methods to show that any sign choice could arise, whereas we have found constraints. This raises the possibility that the correspondence between continuous trace \(C^*\)-algebras and groupoids for the Real case is not a straightforward generalisation of the complex case.
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Communicated by X. Yin
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The authors acknowledge support under the Australian Research Council’s Discovery Projects funding scheme (project numbers DP120100106, DP130102578 and DP180100383), the Consolidated Grant ST/P000363/1 from the UK Science and Technology Facilities Council, the Marsden Foundation (project number 3713803), and the Action MP1405 QSPACE from the European Cooperation in Science and Technology (COST).
We thank David Baraglia and Jonathan Rosenberg for helpful discussions.
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Hekmati, P., Murray, M.K., Szabo, R.J. et al. Sign Choices for Orientifolds. Commun. Math. Phys. 378, 1843–1873 (2020). https://doi.org/10.1007/s00220-020-03831-z
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DOI: https://doi.org/10.1007/s00220-020-03831-z