@article {Piazzalunga2014,
	title = {M-theory interpretation of the real topological string},
	journal = {Journal of High Energy Physics},
	volume = {2014},
	number = {8},
	year = {2014},
	month = {Aug},
	pages = {54},
	abstract = {<p>We describe the type IIA physical realization of the unoriented topological string introduced by Walcher, describe its M-theory lift, and show that it allows to compute the open and unoriented topological amplitude in terms of one-loop diagram of BPS M2-brane states. This confirms and allows to generalize the conjectured BPS integer expansion of the topological amplitude. The M-theory lift of the orientifold is freely acting on the M-theory circle, so that integer multiplicities are a weighted version of the (equivariant subsector of the) original closed oriented Gopakumar-Vafa invariants. The M-theory lift also provides new perspective on the topological tadpole cancellation conditions. We finally comment on the M-theory version of other unoriented topological strings, and clarify certain misidentifications in earlier discussions in the literature.</p>},
	issn = {1029-8479},
	doi = {10.1007/JHEP08(2014)054},
	url = {https://doi.org/10.1007/JHEP08(2014)054},
	author = {Nicol{\`o} Piazzalunga and Uranga, Angel M.}
}
