5,465 research outputs found
CMB Anisotropies Reveal Quantized Gravity
A novel primordial spectrum with a dynamical scale of quantum gravity origin
is proposed to explain the sharp fall off of the angular power spectra at low
multipoles in the COBE and WMAP observations. The spectrum is derived from
quantum fluctuations of the scalar curvature in a renormalizable model of
induced gravity. This model describes the very early universe by the conformal
field fluctuating about an inflationary background with the expansion time
constant of order of the Planck mass.Comment: 12 pages, 2 figure
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
Role of covalency in the ground state properties of perovskite ruthenates: A first principle study using local spin density approximations
We investigate the electronic structure of SrRuO3 and CaRuO3 using full
potential linearized augmented plane wave method within the local spin density
approximations. The ferromagnetic ground state in SrRuO3 could exactly be
described in these calculations and the calculated spin magnetic moment is
found to be close to the experimentally observed values. Interestingly, the
spin polarized calculations for CaRuO3 exhibit large spin moment as observed in
the experiments but the magnetic ground state has higher energy than that in
the non-magnetic solution. Various calculations for different structural
configurations indicate that Ca-O covalency plays the key role in determining
the electronic structure and thereby the magnetic ground state in this system.Comment: 8 figure
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
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
Recursion Relations in Liouville Gravity coupled to Ising Model satisfying Fusion Rules
The recursion relations of 2D quantum gravity coupled to the Ising model
discussed by the author previously are reexamined. We study the case in which
the matter sector satisfies the fusion rules and only the primary operators
inside the Kac table contribute. The theory involves unregularized divergences
in some of correlators. We obtain the recursion relations which form a closed
set among well-defined correlators on sphere, but they do not have a beautiful
structure that the bosonized theory has and also give an inconsistent result
when they include an ill-defined correlator with the divergence. We solve them
and compute the several normalization independent ratios of the well-defined
correlators, which agree with the matrix model results.Comment: Latex, 22 page
Bosonization Theory of Excitons in One-dimensional Narrow Gap Semiconductors
Excitons in one-dimensional narrow gap semiconductors of anti-crossing
quantum Hall edge states are investigated using a bosonization method. The
excitonic states are studied by mapping the problem into a non-integrable
sine-Gordon type model. We also find that many-body interactions lead to a
strong enhancement of the band gap. We have estimated when an exciton
instability may occur.Comment: 4pages, 1 figure, to appear in Phys. Rev. B Brief Report
Exploring spatial patterns of GCM projection bias via model based geostatistics.
General Circulation Models (GCMs) are numerical models developed to represent physical processes in the atmosphere, ocean, cryosphere and land surface. They constitute the most advanced tool currently available for simulating future climate scenarios as a response to increasing greenhouse gas concentrations. GCMs, possibly in conjunction with nested regional climate models (RCMs), have the potential to provide consistent estimates of regional climate change which are required in climate impact assessments. The characterization of model bias in terms of magnitude and spatial patterns is part of the process of evaluating the model performance via hindcast skill analysis, an important preliminary step in climate change impact assessments. In this paper, we discuss how Model Based Geostatistics can be applied for exploring bias patterns, key information for performing bias correction of GCM or RCM projections in future time slices. As example, we present an assessment of annual rainfall projection bias for three GCMs across the Northeast Brazil
Oscillator Strength of Metallic Carbon Nanotubes
Based on the tight binding method with hopping integral between the
nearest-neighbor atoms, an oscillator strength \int_0^{\infty} \d \omega {\rm
Re} \sigma (\omega) is discussed for armchair and metallic zigzag carbon
nanotubes. The formulae of the oscillator strength are derived for both types
of nanotubes and are compared with the result obtained by a linear chain model.
In addition, the doping dependence is investigated in the absence of Coulomb
interaction. It is shown that the oscillator strength of each carbon nanotube
shows qualitatively the same doping dependence, but the fine structure is
different due to it's own peculiar band structure. Some relations independent
of the radius of the tube are derived, and a useful formula for determining the
amount of doping is proposed.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jpn. at June 30, 200
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