1,395 research outputs found
Computing Black Hole entropy in Loop Quantum Gravity from a Conformal Field Theory perspective
Motivated by the analogy proposed by Witten between Chern-Simons and
Conformal Field Theories, we explore an alternative way of computing the
entropy of a black hole starting from the isolated horizon framework in Loop
Quantum Gravity. The consistency of the result opens a window for the interplay
between Conformal Field Theory and the description of black holes in Loop
Quantum Gravity.Comment: 9 page
Effect of the curvature and the {\beta} parameter on the nonlinear dynamics of a drift tearing magnetic island
We present numerical simulation studies of 2D reduced MHD equations
investigating the impact of the electronic \beta parameter and of curvature
effects on the nonlinear evolution of drift tearing islands. We observe a
bifurcation phenomenon that leads to an amplification of the pressure energy,
the generation of E \times B poloidal flow and a nonlinear diamagnetic drift
that affects the rotation of the magnetic island. These dynamical modifications
arise due to quasilinear effects that generate a zonal flow at the onset point
of the bifurcation. Our simulations show that the transition point is
influenced by the \beta parameter such that the pressure gradient through a
curvature effect strongly stabilizes the transition. Regarding the modified
rotation of the island, a model for the frequency is derived in order to study
its origin and the effect of the \beta parameter. It appears that after the
transition, an E \times B poloidal flow as well as a nonlinear diamagnetic
drift are generated due to an amplification of the stresses by pressure
effects
Large non-Gaussian Halo Bias from Single Field Inflation
We calculate Large Scale Structure observables for non-Gaussianity arising
from non-Bunch-Davies initial states in single field inflation. These scenarios
can have substantial primordial non-Gaussianity from squeezed (but observable)
momentum configurations. They generate a term in the halo bias that may be more
strongly scale-dependent than the contribution from the local ansatz. We also
discuss theoretical considerations required to generate an observable
signature.Comment: 30 pages, 14 figures, typos corrected and minor changes to match
published version JCAP09(2012)00
Loop Quantum Gravity and the The Planck Regime of Cosmology
The very early universe provides the best arena we currently have to test
quantum gravity theories. The success of the inflationary paradigm in
accounting for the observed inhomogeneities in the cosmic microwave background
already illustrates this point to a certain extent because the paradigm is
based on quantum field theory on the curved cosmological space-times. However,
this analysis excludes the Planck era because the background space-time
satisfies Einstein's equations all the way back to the big bang singularity.
Using techniques from loop quantum gravity, the paradigm has now been extended
to a self-consistent theory from the Planck regime to the onset of inflation,
covering some 11 orders of magnitude in curvature. In addition, for a narrow
window of initial conditions, there are departures from the standard paradigm,
with novel effects, such as a modification of the consistency relation
involving the scalar and tensor power spectra and a new source for
non-Gaussianities. Thus, the genesis of the large scale structure of the
universe can be traced back to quantum gravity fluctuations \emph{in the Planck
regime}. This report provides a bird's eye view of these developments for the
general relativity community.Comment: 23 pages, 4 figures. Plenary talk at the Conference: Relativity and
Gravitation: 100 Years after Einstein in Prague. To appear in the Proceedings
to be published by Edition Open Access. Summarizes results that appeared in
journal articles [2-13
Detailed black hole state counting in loop quantum gravity
We give a complete and detailed description of the computation of black hole
entropy in loop quantum gravity by employing the most recently introduced
number-theoretic and combinatorial methods. The use of these techniques allows
us to perform a detailed analysis of the precise structure of the entropy
spectrum for small black holes, showing some relevant features that were not
discernible in previous computations. The ability to manipulate and understand
the spectrum up to the level of detail that we describe in the paper is a
crucial step towards obtaining the behavior of entropy in the asymptotic (large
horizon area) regime
Conformal Symmetry for General Black Holes
We show that the warp factor of a generic asymptotically flat black hole in
five dimensions can be adjusted such that a conformal symmetry emerges. The
construction preserves all near horizon properties of the black holes, such as
the thermodynamic potentials and the entropy. We interpret the geometry with
modified asymptotic behavior as the "bare" black hole, with the ambient flat
space removed. Our warp factor subtraction generalizes hidden conformal
symmetry and applies whether or not rotation is significant. We also find a
relation to standard AdS/CFT correspondence by embedding the black holes in six
dimensions. The asymptotic conformal symmetry guarantees a dual CFT description
of the general rotating black holes.Comment: 26 page
Electric-magnetic duality and renormalization in curved spacetimes
We point out that the duality symmetry of free electromagnetism does not hold in the quantum theory if an arbitrary classical gravitational background is present. The symmetry breaks in the process of renormalization, as also happens with conformal invariance. We show that a similar duality anomaly appears for a massless scalar field in 1 + 1 dimensions
Numerical loop quantum cosmology: an overview
A brief review of various numerical techniques used in loop quantum cosmology
and results is presented. These include the way extensive numerical simulations
shed insights on the resolution of classical singularities, resulting in the
key prediction of the bounce at the Planck scale in different models, and the
numerical methods used to analyze the properties of the quantum difference
operator and the von Neumann stability issues. Using the quantization of a
massless scalar field in an isotropic spacetime as a template, an attempt is
made to highlight the complementarity of different methods to gain
understanding of the new physics emerging from the quantum theory. Open
directions which need to be explored with more refined numerical methods are
discussed.Comment: 33 Pages, 4 figures. Invited contribution to appear in Classical and
Quantum Gravity special issue on Non-Astrophysical Numerical Relativit
Loop Quantum Cosmology: A Status Report
The goal of this article is to provide an overview of the current state of
the art in loop quantum cosmology for three sets of audiences: young
researchers interested in entering this area; the quantum gravity community in
general; and, cosmologists who wish to apply loop quantum cosmology to probe
modifications in the standard paradigm of the early universe. An effort has
been made to streamline the material so that, as described at the end of
section I, each of these communities can read only the sections they are most
interested in, without a loss of continuity.Comment: 138 pages, 15 figures. Invited Topical Review, To appear in Classical
and Quantum Gravity. Typos corrected, clarifications and references adde
"Charged" Particle's Tunneling from Rotating Black Holes
The behavior of a scalar field theory near the event horizon in a rotating
black hole background can be effectively described by a two dimensional field
theory in a gauge field background. Based on this fact, we proposal that the
quantum tunneling from rotating black hole can be treated as "charged"
particle' s tunneling process in its effectively two dimensional metric. Using
this viewpoint and considering the corresponding "gauge charge" conservation,
we calculate the non-thermal tunneling rate of Kerr black hole and Myers-Perry
black hole, and results are consistent with Parikh-Wilczek's original result
for spherically symmetric black holes. Especially for Myers-Perry black hole
which has multi-rotation parameters, our calculation fills in the gap existing
in the literature applying Parikh-Wilczek's tunneling method to various types
black holes. Our derivation further illuminates the essential role of effective
gauge symmetry in Hawking radiation from rotating black holes.Comment: 15 pages, no figure; any comments are welcome
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