Abstract. This paper is an introduction to Homological Mirror Symmetry, derived categories, and topological D-branes aimed mainly at a mathematical audience. In the paper we explain the physicists' viewpoint of the Mirror Phenomenon, its relation to derived categories, and the reason why it is necessary to enlarge the Fukaya category with coisotropic A-branes; we discuss how to extend the definition of Floer homology to such objects and describe mirror symmetry for flat tori. The paper consists of four lectures which were given at the Institute for Pure and Applied Mathematics (Los Angeles), March 2003, as part of a program on Symplectic Geometry and Physics.
Mirror Symmetry From a Physical ViewpointThe goal of the first lecture is to explain the physicists' viewpoint of the Mirror Phenomenon and its interpretation in mathematical terms proposed by Maxim Kontsevich in his 1994 talk at the International Congress of Mathematicians [25]. Another approach to Mirror Symmetry was proposed by A. Strominger, S-T. Yau, and E. Zaslow [41], but we will not discuss it here.From the physical point of view, Mirror Symmetry is a relation on the set of 2d conformal field theories with N = 2 supersymmetry. A 2d conformal field theory is a rather complicated algebraic object whose definition will be sketched in a moment. Thus Mirror Symmetry originates in the realm of algebra. Geometry will appear later, when we specialize to a particular class of N = 2 superconformal field theories related to Calabi-Yau manifolds.Let us start with 2d conformal field theory. The data needed to specify a 2d CFT consist of an infinite-dimensional vector space V (the space of states), three special elements in V (the vacuum vector |vac , and two more elements L andL ), and a linear map Y from V to the space of "formal fractional power series in z,z with coefficients in End(V ) " ( Y is called the state-operator correspondence). The precise definition of what a "formal fractional power series" means can be found in [19]; to keep things simple, one can pretend that Y takes values in the space of Laurent series in z,z with coefficients in End(V ), although such a definition is not sufficient for applications to Mirror Symmetry. These data must satisfy a number of axioms whose precise form can be found in [19]. Roughly speaking, they are (i) Y (|vac ) = id V .