Topological conformal field theory with a rational W potential and the dispersionless KP hierarchy

We present a new class of topological conformal field theories (TCFT) characterized by a rational $W$ potential, which includes the minimal models of A and D types as its subclasses. An explicit form of the $W$ potential is found by solving the underlying dispersionless KP hierarchy in a particular small phase space. We discuss also the dispersionless KP hierarchy in large phase spaces by reformulating the hierarchy, and show that the $W$ potential takes a universal form, which does not depend on a specific form of the solution in a large space.