2005 Volume 60 Issue 11 Pages 850-859
Topological string was initially introduced as a "toy model" of string theory, but the author and his collaborators discovered that it can be directly applied to problems in superstring theory, which is a unified theory of elementary particles including gravity. We will discuss how topological string theory is used to address important questions in elementary particle physics such as quantum states of black holes and strongly coupled problems in four-dimensional gauge theories.