We study BPS bound states of D0 and D2 branes on a single D6 brane wrapping a Calabi-Yau 3-fold . When has no compact 4-cyles, the BPS bound states are organized into a free field Fock space, whose generators correspond to BPS states of spinning M2 branes in M-theory compactified down to 5 dimensions by a Calabi-Yau 3-fold . The generating function of the D-brane bound states is expressed as a reduction of the square of the topological string partition function, in all chambers of the Kähler moduli space.
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Mina Aganagic, Hirosi Ooguri, Cumrun Vafa, Masahito Yamazaki, Wall Crossing and M-Theory. Publ. Res. Inst. Math. Sci. 47 (2011), no. 2, pp. 569–584