737 research outputs found

### Relativistic Effects on the Appearance of a Clothed Black Hole

For an accretion disk around a black hole, the strong relativistic effects
affect every aspect of the radiation from the disk, including its spectrum,
light-curve, and image. This work investigates in detail how the images of a
thin disk around a black hole will be distorted, and what the observer will see
from different viewing angles and in different energy bands.Comment: 4 pages, 5 figures. Based on the poster presented at the Sixth
Pacific Rim Conference on Stellar Astrophysics (Xi'an, China, July 11-17,
2002). Color versions of figures are given separatel

### Complementarity Endures: No Firewall for an Infalling Observer

We argue that the complementarity picture, as interpreted as a reference
frame change represented in quantum gravitational Hilbert space, does not
suffer from the "firewall paradox" recently discussed by Almheiri, Marolf,
Polchinski, and Sully. A quantum state described by a distant observer evolves
unitarily, with the evolution law well approximated by semi-classical field
equations in the region away from the (stretched) horizon. And yet, a classical
infalling observer does not see a violation of the equivalence principle, and
thus a firewall, at the horizon. The resolution of the paradox lies in careful
considerations on how a (semi-)classical world arises in unitary quantum
mechanics describing the whole universe/multiverse.Comment: 11 pages, 1 figure; clarifications and minor revisions; v3: a small
calculation added for clarification; v4: some corrections, conclusion
unchange

### Quantum Cosmology for the General Bianchi Type II, VI(Class A) and VII(Class A) vacuum geometries

The canonical quantization of the most general minisuperspace actions --i.e.
with all six scale factor as well as the lapse function and the shift vector
present-- describing the vacuum type II, VI and VII geometries, is considered.
The reduction to the corresponding physical degrees of freedom is achieved
through the usage of the linear constraints as well as the quantum version of
the entire set of classical integrals of motion.Comment: 23 pages, LaTeX2e, No figure

### A note on wavemap-tensor cosmologies

We examine theories of gravity which include finitely many coupled scalar
fields with arbitrary couplings to the curvature (wavemaps). We show that the
most general scalar-tensor $\sigma$-model action is conformally equivalent to
general relativity with a minimally coupled wavemap with a particular target
metric. Inflation on the source manifold is then shown to occur in a novel way
due to the combined effect of arbitrary curvature couplings and wavemap
self-interactions. A new interpretation of the conformal equivalence theorem
proved for such `wavemap-tensor' theories through brane-bulk dynamics is also
discussed.Comment: 8 pages, LaTeX, to appear in the Proceedings of the 2nd Hellenic
Cosmology Workshop, National Observatory of Athens, April 21-22, 2001,
(Kluwer 2001

### Large entropy production inside black holes: a simple model

Particles dropped into a rotating black hole can collide near the inner
horizon with enormous energies. The entropy produced by these collisions can be
several times larger than the increase in the horizon entropy due to the
addition of the particles. In this paper entropy is produced by releasing large
numbers of neutrons near the outer horizon of a rotating black hole such that
they collide near the inner horizon at energies similar to those achieved at
the Relativistic Heavy Ion Collider. The increase in horizon entropy is
approximately 80 per dropped neutron pair, while the entropy produced in the
collisions is 160 per neutron pair. The collision entropy is produced inside
the horizon, so this excess entropy production does not violate Bousso's bound
limiting the entropy that can go through the black hole's horizon. The
generalized laws of black hole thermodynamics are obeyed. No individual
observer inside the black hole sees a violation of the second law of
thermodynamicsComment: 10 page

### Black Hole Emission in String Theory and the String Phase of Black Holes

String theory properly describes black-hole evaporation. The quantum string
emission by Black Holes is computed. The black-hole temperature is the Hawking
temperature in the semiclassical quantum field theory (QFT) regime and becomes
the intrinsic string temperature, T_s, in the quantum (last stage) string
regime. The QFT-Hawking temperature T_H is upper bounded by the string
temperature T_S. The black hole emission spectrum is an incomplete gamma
function of (T_H - T_S). For T_H << T_S, it yields the QFT-Hawking emission.
For T_H \to T_S, it shows highly massive string states dominate the emission
and undergo a typical string phase transition to a microscopic `minimal' black
hole of mass M_{\min} or radius r_{\min} (inversely proportional to T_S) and
string temperature T_S. The string back reaction effect (selfconsistent black
hole solution of the semiclassical Einstein equations) is computed. Both, the
QFT and string black hole regimes are well defined and bounded.The string
`minimal' black hole has a life time tau_{min} simeq (k_B c)/(G hbar [T_S]^3).
The semiclassical QFT black hole (of mass M and temperature T_H) and the string
black hole (of mass M_{min} and temperature T_S) are mapped one into another by
a `Dual' transform which links classical/QFT and quantum string regimes.Comment: LaTex, 22 pages, Lectures delivered at the Chalonge School, Nato ASI:
Phase Transitions in the Early Universe: Theory and Observations. To appear
in the Proceedings, Editors H. J. de Vega, I. Khalatnikov, N. Sanchez.
(Kluwer Pub

### The information paradox: conflicts and resolutions

Many relativists have been long convinced that black hole evaporation leads
to information loss or remnants. String theorists have however not been too
worried about the issue, largely due to a belief that the Hawking argument for
information loss is flawed in its details. A recently derived inequality shows
that the Hawking argument for black holes with horizon can in fact be made
rigorous. What happens instead is that in string theory black hole microstates
have no horizons. Thus the evolution of radiation quanta with E ~ kT is
modified by order unity at the horizon, and we resolve the information paradox.
We discuss how it is still possible for E >> kT objects to see an approximate
black hole like geometry. We also note some possible implications of this
physics for the early Universe.Comment: 26 pages, 8 figures, Latex; (Expanded version of) proceedings for
Lepton-Photon 201

### Quantum Back Reaction to asymptotically AdS Black Holes

We analyze the effects of the back reaction due to a conformal field theory
(CFT) on a black hole spacetime with negative cosmological constant. We study
the geometry numerically obtained by taking into account the energy momentum
tensor of CFT approximated by a radiation fluid. We find a sequence of
configurations without a horizon in thermal equilibrium (CFT stars), followed
by a sequence of configurations with a horizon. We discuss the thermodynamic
properties of the system and how back reaction effects alter the space-time
structure. We also provide an interpretation of the above sequence of solutions
in terms of the AdS/CFT correspondence. The dual five-dimensional description
is given by the Karch-Randall model, in which a sequence of five-dimensional
floating black holes followed by a sequence of brane localized black holes
correspond to the above solutions.Comment: 13 pages, 10 figure

### The foundations of statistical mechanics from entanglement: Individual states vs. averages

We consider an alternative approach to the foundations of statistical
mechanics, in which subjective randomness, ensemble-averaging or time-averaging
are not required. Instead, the universe (i.e. the system together with a
sufficiently large environment) is in a quantum pure state subject to a global
constraint, and thermalisation results from entanglement between system and
environment. We formulate and prove a "General Canonical Principle", which
states that the system will be thermalised for almost all pure states of the
universe, and provide rigorous quantitative bounds using Levy's Lemma.Comment: 12 pages, v3 title changed, v2 minor change

### Hermitian Yang-Mills instantons on resolutions of Calabi-Yau cones

We study the construction of Hermitian Yang-Mills instantons over resolutions
of Calabi-Yau cones of arbitrary dimension. In particular, in d complex
dimensions, we present an infinite family, parametrised by an integer k and a
continuous modulus, of SU(d) instantons. A detailed study of their properties,
including the computation of the instanton numbers is provided. We also explain
how they can be used in the construction of heterotic non-Kahler
compactifications.Comment: 20 pages, 1 figure; typos corrected, section 3.1 expande

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