Blushift of tachyon in the charged 2D black hole

We study the propagation of string fields (metric G_{\mu\nu}, Mawxell gauge potential A_{\mu}, dilaton \Phi, and tachyon T) in a two-dimensional (2D) charged black hole. It is shown that the tachyon is a propagating field both inside and outside the black hole. This becomes infinitely blueshifted at the inner horizon. We confirm that the inner horizon is unstable, whereas the outer horizon is stable