9,128 research outputs found
Quantum Gravity and Black Hole Dynamics in 1+1 Dimensions
We study the quantum theory of 1+1 dimensional dilaton gravity, which is an
interesting toy model of the black hole dynamics. The functional measures are
explicitly evaluated and the physical state conditions corresponding to the
Hamiltonian and the momentum constraints are derived. It is pointed out that
the constraints form the Virasoro algebra without central charge. In ADM
formalism the measures are very ambiguous, but in our formalism they are
explicitly defined. Then the new features which are not seen in ADM formalism
come out. A singularity appears at \df^2 =\kappa (>0) , where and is the number of matter fields. Behind the singularity
the quantum mechanical region \kappa > \df^2 >0 extends, where the sign of
the kinetic term in the Hamiltonian constraint changes. If , the
singularity disappears. We discuss the quantum dynamics of black hole and then
give a suggestion for the resolution of the information loss paradox. We also
argue the quantization of the spherically symmetric gravitational system in 3+1
dimensions. In appendix the differences between the other quantum dilaton
gravities and ours are clarified and our status is stressed.Comment: phyztex, UT-Komaba 92-14. A few misleading sentences are corrected
and some references are adde
On the dynamics of vortex modes within magnetic islands
Recent work investigating the interaction of magnetic islands with
micro-turbulence has uncovered the striking observation of large scale vortex
modes forming within the island structure [W.A. Hornsby {\it et al.}, Phys.
Plasmas {\bf 17} 092301 (2010)]. These electrostatic vortices are found to be
the size of the island and are oscillatory. It is this oscillatory behaviour
and the presence of turbulence that leads us to believe that the dynamics are
related to the Geodesic Acoustic Mode (GAM), and it is this link that is
investigated in this paper.
Here we derive an equation for the GAM in the MHD limit, in the presence of a
magnetic island modified three-dimensional axisymmetric geometry. The
eigenvalues and eigenfunctions are calculated numerically and then utilised to
analyse the dynamics of oscillatory large-scale electrostatic potential
structures seen in both linear and non-linear gyro-kinetic simulations
Vertex Operators in 4D Quantum Gravity Formulated as CFT
We study vertex operators in 4D conformal field theory derived from quantized
gravity, whose dynamics is governed by the Wess-Zumino action by Riegert and
the Weyl action. Conformal symmetry is equal to diffeomorphism symmetry in the
ultraviolet limit, which mixes positive-metric and negative-metric modes of the
gravitational field and thus these modes cannot be treated separately in
physical operators. In this paper, we construct gravitational vertex operators
such as the Ricci scalar, defined as space-time volume integrals of them are
invariant under conformal transformations. Short distance singularities of
these operator products are computed and it is shown that their coefficients
have physically correct sign. Furthermore, we show that conformal algebra holds
even in the system perturbed by the cosmological constant vertex operator as in
the case of the Liouville theory shown by Curtright and Thorn.Comment: 26 pages, rewrote review part concisely, added explanation
Making a Universe
For understanding the origin of anisotropies in the cosmic microwave
background, rules to construct a quantized universe is proposed based on the
dynamical triangulation method of the simplicial quantum gravity. A
-dimensional universe having the topology is created numerically in
terms of a simplicial manifold with -simplices as the building blocks. The
space coordinates of a universe are identified on the boundary surface , and the time coordinate is defined along the direction perpendicular
to . Numerical simulations are made mainly for 2-dimensional
universes, and analyzed to examine appropriateness of the construction rules by
comparing to analytic results of the matrix model and the Liouville theory.
Furthermore, a simulation in 4-dimension is made, and the result suggests an
ability to analyze the observations on anisotropies by comparing to the scalar
curvature correlation of a -surface formed as the last scattering
surface in the universe.Comment: 27pages,18figures,using jpsj.st
Teleportation and entanglement distillation in the presence of correlation among bipartite mixed states
The teleportation channel associated with an arbitrary bipartite state
denotes the map that represents the change suffered by a teleported state when
the bipartite state is used instead of the ideal maximally entangled state for
teleportation. This work presents and proves an explicit expression of the
teleportation channel for the teleportation using Weyl's projective unitary
representation of the space of 2n-tuples of numbers from Z/dZ for integers d>1,
n>0, which has been known for n=1. This formula allows any correlation among
the n bipartite mixed states, and an application shows the existence of
reliable schemes for distillation of entanglement from a sequence of mixed
states with correlation.Comment: 12 pages, 1 figur
A Tuned and Scalable Fast Multipole Method as a Preeminent Algorithm for Exascale Systems
Among the algorithms that are likely to play a major role in future exascale
computing, the fast multipole method (FMM) appears as a rising star. Our
previous recent work showed scaling of an FMM on GPU clusters, with problem
sizes in the order of billions of unknowns. That work led to an extremely
parallel FMM, scaling to thousands of GPUs or tens of thousands of CPUs. This
paper reports on a a campaign of performance tuning and scalability studies
using multi-core CPUs, on the Kraken supercomputer. All kernels in the FMM were
parallelized using OpenMP, and a test using 10^7 particles randomly distributed
in a cube showed 78% efficiency on 8 threads. Tuning of the
particle-to-particle kernel using SIMD instructions resulted in 4x speed-up of
the overall algorithm on single-core tests with 10^3 - 10^7 particles. Parallel
scalability was studied in both strong and weak scaling. The strong scaling
test used 10^8 particles and resulted in 93% parallel efficiency on 2048
processes for the non-SIMD code and 54% for the SIMD-optimized code (which was
still 2x faster). The weak scaling test used 10^6 particles per process, and
resulted in 72% efficiency on 32,768 processes, with the largest calculation
taking about 40 seconds to evaluate more than 32 billion unknowns. This work
builds up evidence for our view that FMM is poised to play a leading role in
exascale computing, and we end the paper with a discussion of the features that
make it a particularly favorable algorithm for the emerging heterogeneous and
massively parallel architectural landscape
Space-Time and Matter in IIB Matrix Model - gauge symmetry and diffeomorphism -
We pursue the study of the type IIB matrix model as a constructive definition
of superstring. In this paper, we justify the interpretation of space-time as
distribution of eigenvalues of the matrices by showing that some low energy
excitations indeed propagate in it. In particular, we show that if the
distribution consists of small clusters of size , low energy theory acquires
local SU(n) gauge symmetry and a plaquette action for the associated gauge
boson is induced, in addition to a gauge invariant kinetic term for a massless
fermion in the adjoint representation of the SU(n). We finally argue a possible
identification of the diffeomorphism symmetry with permutation group acting on
the set of eigenvalues, and show that the general covariance is realized in the
low energy effective theory even though we do not have a manifest general
covariance in the IIB matrix model action.Comment: 25 page
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