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Motivated by recent mathematical developements in non-commutative
Donaldson-Thomas theory, we construct a new statistical mechanical model
of crystal melting to count BPS branes wrapping an arbitrary toric
Calabi-Yau 3-fold. We also discuss the wall crossing phenomena, which
are crucial for the proper understanding of the relation between the
crystal melting and the topological string theory. (Joint work with H.
Ooguri, arXiv:0811.2801 and
arXiv:0902.3996.)
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