804 research outputs found
Quantum Black Hole Evaporation
We investigate a recently proposed model for a full quantum description of
two-dimensional black hole evaporation, in which a reflecting boundary
condition is imposed in the strong coupling region. It is shown that in this
model each initial state is mapped to a well-defined asymptotic out-state,
provided one performs a certain projection in the gravitational zero mode
sector. We find that for an incoming localized energy pulse, the corresponding
out-going state contains approximately thermal radiation, in accordance with
semi-classical predictions. In addition, our model allows for certain acausal
strong coupling effects near the singularity, that give rise to corrections to
the Hawking spectrum and restore the coherence of the out-state. To an
asymptotic observer these corrections appear to originate from behind the
receding apparent horizon and start to influence the out-going state long
before the black hole has emitted most of its mass. Finally, by putting the
system in a finite box, we are able to derive some algebraic properties of the
scattering matrix and prove that the final state contains all initial
information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file),
Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor
corrections, one reference added
U-Duality of Born-Infeld on the Noncommutative Two-Torus
We discuss Born-Infeld on the noncommutative two-torus as a description of compactified string theory. We show that the resulting theory, including the fluctuations, is manifestly invariant under the T-duality group SO(2,2;Z). The BPS mass even has a full SL(3,Z)xSL(2,Z) U-duality symmetry. The direct identification of the noncommutative parameter \theta with the B-field modulus however seems to be problematic at finite volume
A Farey Tail for Attractor Black Holes
The microstates of 4d BPS black holes in IIA string theory compactified on a
Calabi-Yau manifold are counted by a (generalized) elliptic genus of a (0,4)
conformal field theory. By exploiting a spectral flow that relates states with
different charges, and using the Rademacher formula, we find that the elliptic
genus has an exact asymptotic expansion in terms of semi-classical
saddle-points of the dual supergravity theory. This generalizes the known
"Black Hole Farey Tail" of [1] to the case of attractor black holes.Comment: 36 pages, 3 figures, note adde
Black Hole Horizons and Complementarity
We investigate the effect of gravitational back-reaction on the black hole
evaporation process. The standard derivation of Hawking radiation is
re-examined and extended by including gravitational interactions between the
infalling matter and the outgoing radiation. We find that these interactions
lead to substantial effects. In particular, as seen by an outside observer,
they lead to a fast growing uncertainty in the position of the infalling matter
as it approaches the horizon. We argue that this result supports the idea of
black hole complementarity, which states that, in the description of the black
hole system appropriate to outside observers, the region behind the horizon
does not establish itself as a classical region of space-time. We also give a
new formulation of this complementarity principle, which does not make any
specific reference to the location of the black hole horizon.Comment: Some minor modifications in text and the title chang
Wall Crossing, Discrete Attractor Flow and Borcherds Algebra
The appearance of a generalized (or Borcherds-) Kac-Moody algebra in the
spectrum of BPS dyons in N=4, d=4 string theory is elucidated. From the
low-energy supergravity analysis, we identify its root lattice as the lattice
of the T-duality invariants of the dyonic charges, the symmetry group of the
root system as the extended S-duality group PGL(2,Z) of the theory, and the
walls of Weyl chambers as the walls of marginal stability for the relevant
two-centered solutions. This leads to an interpretation for the Weyl group as
the group of wall-crossing, or the group of discrete attractor flows.
Furthermore we propose an equivalence between a "second-quantized multiplicity"
of a charge- and moduli-dependent highest weight vector and the dyon
degeneracy, and show that the wall-crossing formula following from our proposal
agrees with the wall-crossing formula obtained from the supergravity analysis.
This can be thought of as providing a microscopic derivation of the
wall-crossing formula of this theory.Comment: This is a contribution to the Special Issue on Kac-Moody Algebras and
Applications, published in SIGMA (Symmetry, Integrability and Geometry:
Methods and Applications) at http://www.emis.de/journals/SIGMA
Some Unique Constants Associated with Extremal Black Holes
In recent papers we had developed a unified picture of black hole entropy and
curvature which was shown to lead to Hawking radiation. It was shown that for
any black hole mass, holography implies a phase space of just one quantum
associated with the interior of the black hole. Here we study extremal rotating
and charged black holes and obtain unique values for ratios of angular momentum
to entropy, charge to entropy, etc. It turns out that these ratios can be
expressed in terms of fundamental constants in nature, having analogies with
other physical systems, like in condensed matter physics.Comment: "Accepted for publication in Astrophysics & Space Science" 4 pages,
10 equation
Assessment of roll-out potential of CITYLAB solutions to other CITYLAB living labs
This report analyses to what extent the seven CITYLAB implementations may be successfully transferred from their original implementation city to other CITYLAB cities. CITYLAB supports seven Living Labs where innovative urban freight measures are implemented, analysed and rolled out. The focus of this report is to clarify ‘if’ and ‘how’ the seven implementations can be transferred and scaled to the other CITYLAB cities. The CITYLAB cities will learn, from this report, which implementations may be transferred to their own context. Furthermore, they will gain understanding in possibilities to improve the conditions for better chances of a successful transfer of CITYLAB implementations. The transferability methodology adopted in TIDE has been taken as the basis for the CITYLAB methodology as it is the most developed and most relevant to CITYLAB. An appropriate adjustment of the TIDE methodology was necessary as, on the one hand, TIDE examined the transferability of measures in general, while CITYLAB analyses the transferability of applied measures to specific cities. On the other hand, TIDE analysed innovative urban transport and mobility concepts whereas CITYLAB is dealing with the implementation of innovative logistics solutions. The seven consecutive steps of the CITYLAB transferability analysis are: STEP 1: Implementation statement/objectives and scoping STEP 2: Clarification of the impacts of the implementation STEP 3: Identification of upscaling/downscaling needs of implementations STEP 4: Identification of success factors of implementations STEP 5: Identification of the level of importance of success factors STEP 6: Assessment of success factors in the context of adopter city STEP 7: Conclusions on the transferability of implementations The summarized results of the CITYLAB transferability analysis are shown in the chart overview. The ranking shows for each implementation in which CITYLAB city the chance for successful transfer is the best
Gauge Invariant Formulations of Lineal Gravity
It is shown that the currently studied ``string-inspired'' model for gravity
on a line can be formulated as a gauge invariant theory based on the Poincar\'e
group with central extension -- a formulation that complements and simplifies
H.~Verlinde's construction based on the unextended Poincar\'e group.Comment: 11 p
Topological Dilatonic Supergravity Theories
We present a central extension of the super-Poincar\'e algebra in two
dimensions. Besides the usual Poincar\'e generators and the
supersymmetry generators we have Grassmann generators, a bosonic
internal symmetry generator and a central charge. We then build up the
topological gauge theory associated to this algebra. We can solve the classical
field equations for the fields which do not belong to the supergravity
multiplet and to a Lagrange multiplier multiplet. The resulting topological
supergravity theory turns out to be non-local in the fermionic sector.Comment: 11 pages, plain TeX, IFUSP-P/112
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