Odd-integer three-form flux quanta in Calabi–Yau orientifolds

Determine whether three-form flux quantization in type IIB Calabi–Yau orientifolds permits odd integer flux quanta in the absence of exotic O3-planes, thereby establishing if restrictions analogous to those known in toroidal orientifolds apply in this setting.

Background

In toroidal orientifolds, odd integer quanta in certain cycles require exotic O3-planes, imposing nontrivial constraints on allowed fluxes. The authors note that in Calabi–Yau orientifolds the corresponding situation is not settled.

Their constructions allow both odd and even flux quanta but acknowledge that definitive quantization conditions in Calabi–Yau orientifolds remain to be established.