Moduli space of unstable D-branes on a circle of critical radius

Abstract

We study the moduli space of the boundary conformal field theories describing an unstable D-brane of type-II string theory compactified on a circle of critical radius. This moduli space has two branches-a three dimensional branch S³/Z₂ and a two dimensional branch described by a square torus T². These two branches are joined along a circle. We compare this with the moduli space of classical solutions of tachyon effective field theory compactified on a circle of critical radius. This moduli space has a very similar structure to that of the boundary conformal field theory with the only difference that the S³ of the S³/Z₂ component becomes a deformed S³. This provides one more indication that the tachyon effective field theory captures qualitatively the dynamics of the tachyon on an unstable D-brane.