601 research outputs found
Strong Magnetic Limit of String Theory
We show that there exists a certain limit in type I and type II superstring
theory in the presence of a suitable configuration of magnetic U(1) fields
where all string excitations get an infinite mass, except for the neutral
massless sector and for the boson and fermion string states lying on the
leading Regge trajectory. For a supersymmetric configuration of magnetic fields
in internal directions, the resulting theory after the limit is a 3+1 Lorentz
invariant supersymmetric theory. Supersymmetry can be broken by introducing
extra components of the magnetic field or else by finite temperature. In both
cases we compute the one-loop partition function for the type I string model
after taking the limit, which turns out to be different from the Yang-Mills
result that arises by a direct limit. In the case of finite
temperature, no Hagedorn transition appears, in consistency with the reduction
of the string spectrum. In type II superstring theory, the analogous limit is
constructed by starting with a configuration of Melvin twists in two or more
complex planes. The resulting theory contains gravitation plus an infinite
number of states of the leading Regge trajectory.Comment: 10 pages. Minor correction
The string spectrum on the horizon of a non-extremal black hole
We investigate the conformal string -model corresponding to a
general five-dimensional non-extremal black hole solution. In the horizon
region the theory reduces to an exactly solvable conformal field theory. We
determine the modular invariant spectrum of physical string states, which
expresses the Rindler momentum operator in terms of three charges and string
oscillators. For black holes with winding and Kaluza-Klein charges, we find
that states made with only right-moving excitations have ADM mass equal to the
black hole ADM mass, and thus they can be used as sources of the gravitational
field. A discussion on statistical entropy is included.Comment: 17 pages, harvmac (minor corrections
Wormhole phase in the RST model
We show that the RST model describing the exactly soluble black hole model
can have a dynamical wormhole solution along with an appropriate boundary
condition. The necessary exotic matter which is usually negative energy density
is remarkably produced by the quantization of the infalling matter fields. Then
the asymptotic geometry in the past is two-dimensional anti-de Sitter(AdS),
which implies the exotic matter is negative. As time goes on, the wormhole
eventually evolves into the black hole and its Hawking radiation appears. The
throat of the static RST wormhole is lower-bounded but in the presence of
infalling matter it collapses to a black hole.Comment: v1. REVTeX3, 12 pages and 1 figure; v2. JHEP3, 10 pages and 1 figure,
version published in JHE
Fundamental Strings as Black Bodies
We show that the decay spectrum of massive excitations in perturbative string
theories is thermal when averaged over the (many) initial degenerate states. We
first compute the inclusive photon spectrum for open strings at the tree level
showing that a black body spectrum with the Hagedorn temperature emerges in the
averaging. A similar calculation for a massive closed string state with winding
and Kaluza-Klein charges shows that the emitted graviton spectrum is thermal
with a "grey-body" factor, which approaches one near extremality. These results
uncover a simple physical meaning of the Hagedorn temperature and provide an
explicit microscopic derivation of the black body spectrum from a unitary
matrix.Comment: some changes in the Discussion section and in the reference list. 11
pages, Late
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
Consequence of Hawking radiation from 2d dilaton black holes
We investigate the CGHS model through numerical calculation. The behavior of
the mass function, which we introduced in our previous work as a ``local
mass'', is examined. We found that the mass function takes negative values,
which means that the amount of Hawking radiation becomes greater than the
initial mass of the black hole as in the case of the RST model.Comment: 17pages, 5 figures (three of them are attached, the other 2 figures
are available on request. Some mistakes including typographic errors have
been correcte
Entropy in the RST Model
The RST Model is given boundary term and Z-field so that it is well-posed and
local. The Euclidean method is described for general theory and used to
calculate the RST intrinsic entropy. The evolution of this entropy for the
shockwave solutions is found and obeys a second law.Comment: 10 pages, minor revisions, published version in Late
A Quantum Bousso Bound
The Bousso bound requires that one quarter the area of a closed codimension
two spacelike surface exceeds the entropy flux across a certain lightsheet
terminating on the surface. The bound can be violated by quantum effects such
as Hawking radiation. It is proposed that at the quantum level the bound be
modified by adding to the area the quantum entanglement entropy across the
surface. The validity of this quantum Bousso bound is proven in a
two-dimensional large N dilaton gravity theory.Comment: 17 page
T-duality in M-theory and supermembranes
The (q_1,q_2) SL(2,Z) string bound states of type IIB superstring theory
admit two inequivalent (T-dual) representations in eleven dimensions in terms
of a fundamental 2-brane. In both cases, the spectrum of membrane oscillations
can be determined exactly in the limit , where is the
type IIA string coupling. We find that the BPS mass formulas agree, and
reproduce the BPS mass spectrum of the string bound state. In the
non-BPS sector, the respective mass formulas apply in different corners of the
moduli space. The axiomatic requirement of T-duality in M-theory permits to
derive a discrete mass spectrum in a (thin torus) region where standard
supermembrane theory undergoes instabilities.Comment: harvmac, 9 page
Conformal Field Theory for the Superstring in a Ramond-Ramond Plane Wave Background
A quantizable worldsheet action is constructed for the superstring in a
supersymmetric plane wave background with Ramond-Ramond flux. The action is
manifestly invariant under all isometries of the background and is an exact
worldsheet conformal field theory.Comment: 13 pages harvma
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