  We solve the equations of motion of the tachyon and the discrete states in
the background of Witten's semiclassical black hole and in the exact 2D
dilaton-graviton background of Dijkgraaf et al. We find the exact solutions for
weak fields, leading to conclusions in disagreement with previous studies of
tachyons in the black hole. Demanding that a state in the black hole be well
behaved at the horizon implies that it must tend asymptotically to a
combination of a Seiberg and an anti-Seiberg c=1 state. For such a state to be
well behaved asymptotically, it must satisfy the condition that neither its
Seiberg nor its anti-Seiberg Liouville momentum is positive. Thus, although the
free-field BRST cohomologies of the underlying SL(2,R)/U(1) theory is the same
as that of a c=1 theory, the black hole spectrum is drastically truncated:
THERE ARE NO W_INFINITY STATES, AND ONLY TACHYONS WITH X-MOMENTA | P_TACH | <=
| M_TACH | ARE ALLOWED. In the Minkowski case only the static tachyon is
allowed. The black hole is stable to the back reaction of these remaining
tachyons, so they are good perturbations of the black hole, or ``hair''.
However, this leaves only 3 tachyonic hairs in the black hole and 7 in the
exact solution! Such sparse hair is clearly irrelevant to the maintenance of
coherence during black hole evaporation.

High Energy Physics - Theory;General Relativity and Quantum Cosmology