56 research outputs found
Spacetime Geometry as Statistic Ensemble of Strings
Jacobson theorem (Ref. \cite{jacobson}) shows that Einstein gravity may be
understood as a thermodynamical equation of state; a microscopic realization of
this result is however lacking. In this paper, we propose that this may be
achieved by assuming the spacetime geometry as a macroscopic system, whose
thermodynamical behavior is described by a statistical ensemble, whose
microscopic components are low-dimensional geometries. We show that this
picture is consistent with string theory by proposing a particular model for
the microscopic geometry, where the spacetime metric plays the role of an
ordinary thermodynamical potential in a special ensemble. In this scenario,
Einstein equation is indeed recovered as an equation of state, and the black
hole thermodynamics is reproduced in a thermodynamic limit (large length
scales). The model presented here is background-independent and, in particular,
it provides an alternative formulation of string theory.Comment: 14 pages, no figure
Emergent spacetime, and a model for unitary gravitational collapse in AdS
We propose a CFT unitary description of the gravitational collapse. The
starting point is the model of a black hole in AdS proposed by Maldacena in
arXiv: 0106112 [hep-th]. We show that by proposing a two-copies version of the
AdS/CFT conjecture, the process of formation of black holes so as other
spacetimes with horizons may be described as an unitary process in the dual
field theory. In doing this, we construct a well defined framework to describe
general spacetimes as entangled states, in terms of the spectrum of states on
the exact Anti-de-Sitter background. As application, we show how the
description of the Hawking-Page transition results simplified in this formalism
and some novel aspects may be observed. Finally, a simplified analysis based on
weakly coupled bulk fields is discussed.Comment: 19 pages, 1 figur
Area Operators in Holographic Quantum Gravity
We argue that the holographic formula relating entanglement entropy and the
area of a minimal surface is the key to define the area of surfaces in the
(emergent) spacetime from the dual theory on the boundary. So we promote the
entropy/area relation to operators to define the "area" observable in a
holographic formulation of quantum gravity, then we find a suitable geometric
representation for the states, and show that the Ryu-Takayanagi proposal is
recovered in the approximation of semi-classical gravity. Finally, we discuss
this picture in the example of a AdS-Black hole.Comment: Essay written for the Gravity Research Foundation 2014 Awards for
Essays on Gravitation. Minor corrections. Figure and reference adde
Lorentz Symmetry Breaking and Planar Effects from Non-Linear Electrodynamics
We propose a modification of standard linear electrodynamics in four
dimensions, where effective non-trivial interactions of the electromagnetic
field with itself and with matter fields induce Lorentz violating Chern-Simons
terms. This yields two consequences: it provides a more realistic and general
scenario for the breakdown of Lorentz symmetry in electromagnetism and it may
explain the effective behavior of the electromagnetic field in certain planar
phenomena (for instance, Hall effect). A number of proposals for non-linear
electrodynamics is discussed along the paper. Important physical implications
of the breaking of Lorentz symmetry, such as optical birefringence and the
possibility of having conductance in the vacuum are commented on
Einstein-Cartan formulation of Chern-Simons Lorentz-violating Gravity
We consider a modification of the standard Einstein theory in four
dimensions, alternative to R. Jackiw and S.-Y. Pi, Phys. Rev. D 68, 104012
(2003), since it is based on the first-order (Einstein-Cartan) approach to
General Relativity, whose gauge structure is manifest. This is done by
introducing an additional topological term in the action which becomes a
Lorentz-violating term by virtue of the dependence of the coupling on the
space-time point. We obtain a condition on the solutions of the Einstein
equations, such that they persist in the deformed theory, and show that the
solutions remarkably correspond to the classical solutions of a collection of
independent 2+1-d (topological) Chern-Simons gravities. Finally, we study the
relation with the standard second-order approach and argue that they both
coincide to leading order in the modulus of the Lorentz-violating vector field.Comment: Final versio
Which quantum states are dual to classical spacetimes?
It is commonly accepted that states in a conformal field theory correspond to
classical spacetimes with Anti-de-Sitter asymptotics. In this work we give a
prescription for the CFT states with a dual classical spacetime and, using
basic holographic rules, show that they are holographically connected to
coherent states in the large-N limit, or by considering linearized
perturbations. We also point out implications in the spacetime emergence
mechanism, for instance, the (entangled) state dual to the black hole should be
properly described as a quantum superposition of products of these states. This
also complements the quantum interpretation of the Hawking-Page transition.Comment: 14 pages, 8 figure
String entanglement and D-branes as pure states
We study the entanglement of closed strings degrees of freedom in order to investigate the microscopic structure and statistics of objects as D-branes. By considering the macroscopic pure state limit, whenever the entanglement entropy goes to zero (in such a way that the macroscopic properties of the state are preserved), we show that boundary states may be recovered in this limit and, furthermore, the description through closed string (perturbative) degrees of freedom collapses. We also show how the thermal properties of branes and closed strings could be described by this model, and it requires that dissipative effects be taken into account. Extensions of the macroscopic pure state analysis to more general systems at finite temperature are finally emphasized.Instituto de FĂsica La Plat
Wormhole solutions to Horava gravity
We present wormhole solutions to Horava non-relativistic gravity theory in
vacuum. We show that, if the parameter is set to one, transversable
wormholes connecting two asymptotically de Sitter or anti-de Sitter regions
exist. In the case of arbitrary , the asymptotic regions have a more
complicated metric with constant curvature. We also show that, when the
detailed balance condition is violated softly, tranversable and asymptotically
Minkowski, de Sitter or anti-de Sitter wormholes exist.Comment: 17 pages, 1 figure. Replaced by revised version. Includes an appendix
with the proof of the matching condition. References added. Accepted for
publication in Phys.Rev.
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