3 research outputs found
Unitarity Meets Channel-Duality for Rolling / Decaying D-Branes
Investigations for decay of unstable D-brane and rolling of accelerated
D-brane dynamics have revealed that various proposed prescriptions give
different result for spectral amplitudes and observables. Here, we study them
with particular attention to unitarity and open-closed channel duality. From
"ab initio" derivation in the open string channel, both in Euclidean and
Lorentzian worldsheet approaches, we find heretofore overlooked contribution to
the spectral amplitudes and obervables. The contribution is fortuitously absent
for decay of unstable D-brane, but is present for rolling of accelerated
D-brane. We finally show that the contribution is imperative for ensuring
unitarity and optical theorem at each order in string loop expansion.Comment: Latex, 28 pages, 2 figures (colored
D-Brane Propagation in Two-Dimensional Black Hole Geometries
We study propagation of D0-brane in two-dimensional Lorentzian black hole
backgrounds by the method of boundary conformal field theory of SL(2,R)/U(1)
supercoset at level k. Typically, such backgrounds arise as near-horizon
geometries of k coincident non-extremal NS5-branes, where 1/k measures
curvature of the backgrounds in string unit and hence size of string worldsheet
effects. At classical level, string worldsheet effects are suppressed and
D0-brane propagation in the Lorentzian black hole geometry is simply given by
the Wick rotation of D1-brane contour in the Euclidean black hole geometry.
Taking account of string worldsheet effects, boundary state of the Lorentzian
D0-brane is formally constructible via Wick rotation from that of the Euclidean
D1-brane. However, the construction is subject to ambiguities in boundary
conditions. We propose exact boundary states describing the D0-brane, and
clarify physical interpretations of various boundary states constructed from
different boundary conditions. As it falls into the black hole, the D0-brane
radiates off to the horizon and to the infinity. From the boundary states
constructed, we compute physical observables of such radiative process. We find
that part of the radiation to infinity is in effective thermal distribution at
the Hawking temperature. We also find that part of the radiation to horizon is
in the Hagedorn distribution, dominated by massive, highly non-relativistic
closed string states, much like the tachyon matter. Remarkably, such
distribution emerges only after string worldsheet effects are taken exactly
into account. From these results, we observe that nature of the radiation
distribution changes dramatically across the conifold geometry k=1 (k=3 for the
bosonic case), exposing the `string - black hole transition' therein.Comment: 51 pages, 5 figures, v2: referece added, note added replying the
comment made in hep-th/060206
On the origin of thermal string gas
We investigate decaying D-branes as the origin of the thermal string gas of
string gas cosmology. We consider initial configurations of low-dimensional
branes and argue that they can time evolve to thermal string gas. We find that
there is a range in the weak string coupling and fast brane decay time regimes,
where the initial configuration could drive the evolution of the dilaton to
values, where exactly three spacelike directions grow large.Comment: 16 pages, 4 figures, v2: references adde