In the type 0B string theory, we discuss the role of tachyon($T$) and fixed scalars($\nu,\lambda$). The issue is to explain the difference between tachyon and fixed scalars in the D$5_{ \pm}$-D$1_{ \pm}$ black hole background. For this purpose, we perform the semiclassical calculation. Here one finds a mixing between ($\nu, \lambda, T$) and the other fields. Using the decoupling procedure, one finds the linearized equation for the tachyon. From the potential analysis, it turns out that $\nu$ plays a role of test field well, while the tachyon induces an instability of Minkowski space vacuum. But the roles of $\nu$ and $T$ are the same in the near-horizon geometry. Finally we discuss the stability problem.
Categories: hep-th