1,802 research outputs found
B\"acklund transformations in 2D dilaton gravity
We give a B\"acklund transformation connecting a generic 2D dilaton gravity
theory to a generally covariant free field theory. This transformation provides
an explicit canonical transformation relating both theories.Comment: LaTeX file, 7 page
Virasoro Orbits, AdS_3 Quantum Gravity and Entropy
We analyse the canonical structure of AdS_3 gravity in terms of the coadjoint
orbits of the Virasoro group. There is one subset of orbits, associated to BTZ
black hole solutions, that can be described by a pair of chiral free fields
with a background charge. There is also a second subset of orbits, associated
to point-particle solutions, that are described by two pairs of chiral free
fields obeying a constraint. All these orbits admit K\"ahler quantization and
generate a Hilbert space which, despite of having ,
does not provide the right degeneracy to account for the Bekenstein-Hawking
entropy due to the breakdown of modular invariance. Therefore, additional
degrees of freedom, reestablishing modular invariance, are necessarily required
to properly account for the black hole entropy.Comment: LaTex file, 12 pages. New references adde
A Note on Einstein Gravity on AdS and Boundary Conformal Field Theory
We find a simple relation between the first subleading terms in the
asymptotic expansion of the metric field in AdS, obeying the Brown-Henneaux
boundary conditions, and the stress tensor of the underlying Liouville theory
on the boundary. We can also provide an more explicit relation between the bulk
metric and the boundary conformal field theory when it is described in terms of
a free field with a background charge.Comment: LateX file, 10 page
Short distances, black holes, and TeV gravity
The Hawking effect can be rederived in terms of two-point functions and in
such a way that it makes it possible to estimate, within the conventional
semiclassical theory, the contribution of ultrashort distances at to the
Planckian spectrum. Thermality is preserved for black holes with . However, deviations from the Planckian spectrum can be found for mini black
holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: 4 pages. Contribution to the MG11 Meeting (Berlin, July 2006
Acceleration radiation, transition probabilities, and trans-Planckian physics
An important question in the derivation of the acceleration radiation, which
also arises in Hawking's derivation of black hole radiance, is the need to
invoke trans-Planckian physics for the quantum field that originates the
created quanta. We point out that this issue can be further clarified by
reconsidering the analysis in terms of particle detectors, transition
probabilities, and local two-point functions. By writing down separate
expressions for the spontaneous- and induced-transition probabilities of a
uniformly accelerated detector, we show that the bulk of the effect comes from
the natural (non trans-Planckian) scale of the problem, which largely
diminishes the importance of the trans-Planckian sector. This is so, at least,
when trans-Planckian physics is defined in a Lorentz invariant way. This
analysis also suggests how to define and estimate the role of trans-Planckian
physics in the Hawking effect itself.Comment: 19 page
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