16 research outputs found
Estimation of Land Surface Albedo from GCOM-C/SGLI Surface Reflectance
XXIV ISPRS Congress “Imaging today, foreseeing tomorrow, ” Commission III2021 edition, 5–9 July 2021This paper examines algorithms for estimating terrestrial albedo from the products of the Global Change Observation Mission – Climate (GCOM-C)/Second-generation Global Imager (SGLI), which was launched in December 2017 by the Japan Aerospace Exploration Agency. We selected two algorithms: one based on a bidirectional reflectance distribution function (BRDF) model and one based on multi-regression models. The former determines kernel-driven BRDF model parameters from multiple sets of reflectance and estimates the land surface albedo from those parameters. The latter estimates the land surface albedo from a single set of reflectance with multi-regression models. The multi-regression models are derived for an arbitrary geometry from datasets of simulated albedo and multi-angular reflectance. In experiments using in situ multi-temporal data for barren land, deciduous broadleaf forests, and paddy fields, the albedos estimated by the BRDF-based and multi-regression-based algorithms achieve reasonable root-mean-square errors. However, the latter algorithm requires information about the land cover of the pixel of interest, and the variance of its estimated albedo is sensitive to the observation geometry. We therefore conclude that the BRDF-based algorithm is more robust and can be applied to SGLI operational albedo products for various applications, including climate-change research
Open Semiclassical Strings and Long Defect Operators in AdS/dCFT Correspondence
We consider defect composite operators in a defect superconformal field
theory obtained by inserting an AdS_4 x S^2-brane in the AdS_5 x S^5
background. The one-loop dilatation operator for the scalar sector is
represented by an integrable open spin chain. We give a description to
construct coherent states for the open spin chain. Then, by evaluating the
expectation value of the Hamiltonian with the coherent states in a long
operator limit, a Landau-Lifshitz type of sigma model action is obtained. This
action is also derived from the string action and hence we find a complete
agreement in both SYM and string sides. We see that an SO(3)_H pulsating string
solution is included in the action and its energy completely agrees with the
result calculated in a different method. In addition, we argue that our
procedure would be applicable to other AdS-brane cases.Comment: 22 pages, 1 figure, LaTeX, minor corrections and references added.
v3) some new results added. shortened and accepted version in PR
Electron Cloud Instability in SuperKEKB Low Energy Ring
Abstract We study the issue of coherent instabilities due to electron clouds by numerical simulations for SuperKEKB. We first calculate electron cloud density by simulating the motions of the electrons emitted from the chamber wall. By introducing an ante-chamber we can reduce the number of eletrcons emitted from the chamber wall. We evaluate the relation of the electron density and the efficiency of the ante-chember. Next we study a perturbation to the beam motion (bunch by bunch wake field) and the growth rate of the coupled bunch instability. From those studies we estimate the effective value of quantum efficiency safe for avoiding coherent instabilities. Finally the threshold of the electron cloud density for the stability is estimated for SuperKEKB by single bunch numerical simulations
Integrability and Higher Loops in AdS/dCFT Correspondence
We further study the correspondence between open semiclassical strings and
long defect operators which is discussed in our previous work [hep-th/0410139].
We give an interpretation of the spontaneous symmetry breaking of SO(6)->
SO(3)_H x SO(3)_V from the viewpoint of the Riemann surface by following the
argument of Minahan. Then we use the concrete form of the resolvent for a
single cut solution and compute the anomalous dimension of operators dual to an
open pulsating string at three-loop level. In the string side we obtain the
energy of the open pulsating string solution by semiclassical analysis. Both
results agree at two-loop level but we find a three-loop discrepancy.Comment: v1: 11 pages, 2 figures; v2: minor corrections, references added,
published versio
Dominance of a single topological sector in gauge theory on non-commutative geometry
We demonstrate a striking effect of non-commutative (NC) geometry on
topological properties of gauge theory by Monte Carlo simulations. We study 2d
U(1) NC gauge theory for various boundary conditions using a new finite-matrix
formulation proposed recently. We find that a single topological sector
dictated by the boundary condition dominates in the continuum limit. This is in
sharp contrast to the results in commutative space-time based on lattice gauge
theory, where all topological sectors appear with certain weights in the
continuum limit. We discuss possible implications of this effect in the context
of string theory compactifications and in field theory contexts.Comment: 16 pages, 27 figures, typos correcte
Probability distribution of the index in gauge theory on 2d non-commutative geometry
We investigate the effects of non-commutative geometry on the topological
aspects of gauge theory using a non-perturbative formulation based on the
twisted reduced model. The configuration space is decomposed into topological
sectors labeled by the index nu of the overlap Dirac operator satisfying the
Ginsparg-Wilson relation. We study the probability distribution of nu by Monte
Carlo simulation of the U(1) gauge theory on 2d non-commutative space with
periodic boundary conditions. In general the distribution is asymmetric under
nu -> -nu, reflecting the parity violation due to non-commutative geometry. In
the continuum and infinite-volume limits, however, the distribution turns out
to be dominated by the topologically trivial sector. This conclusion is
consistent with the instanton calculus in the continuum theory. However, it is
in striking contrast to the known results in the commutative case obtained from
lattice simulation, where the distribution is Gaussian in a finite volume, but
the width diverges in the infinite-volume limit. We also calculate the average
action in each topological sector, and provide deeper understanding of the
observed phenomenon.Comment: 16 pages,10 figures, version appeared in JHE
A non-perturbative study of 4d U(1) non-commutative gauge theory -- the fate of one-loop instability
Recent perturbative studies show that in 4d non-commutative spaces, the
trivial (classically stable) vacuum of gauge theories becomes unstable at the
quantum level, unless one introduces sufficiently many fermionic degrees of
freedom. This is due to a negative IR-singular term in the one-loop effective
potential, which appears as a result of the UV/IR mixing. We study such a
system non-perturbatively in the case of pure U(1) gauge theory in four
dimensions, where two directions are non-commutative. Monte Carlo simulations
are performed after mapping the regularized theory onto a U(N) lattice gauge
theory in d=2. At intermediate coupling strength, we find a phase in which open
Wilson lines acquire non-zero vacuum expectation values, which implies the
spontaneous breakdown of translational invariance. In this phase, various
physical quantities obey clear scaling behaviors in the continuum limit with a
fixed non-commutativity parameter , which provides evidence for a
possible continuum theory. The extent of the dynamically generated space in the
non-commutative directions becomes finite in the above limit, and its
dependence on is evaluated explicitly. We also study the dispersion
relation. In the weak coupling symmetric phase, it involves a negative
IR-singular term, which is responsible for the observed phase transition. In
the broken phase, it reveals the existence of the Nambu-Goldstone mode
associated with the spontaneous symmetry breaking.Comment: 29 pages, 23 figures, references adde
The index of the overlap Dirac operator on a discretized 2d non-commutative torus
The index, which is given in terms of the number of zero modes of the Dirac
operator with definite chirality, plays a central role in various topological
aspects of gauge theories. We investigate its properties in non-commutative
geometry. As a simple example, we consider the U(1) gauge theory on a
discretized 2d non-commutative torus, in which general classical solutions are
known. For such backgrounds we calculate the index of the overlap Dirac
operator satisfying the Ginsparg-Wilson relation. When the action is small, the
topological charge defined by a naive discretization takes approximately
integer values, and it agrees with the index as suggested by the index theorem.
Under the same condition, the value of the index turns out to be a multiple of
N, the size of the 2d lattice. By interpolating the classical solutions, we
construct explicit configurations, for which the index is of order 1, but the
action becomes of order N. Our results suggest that the probability of
obtaining a non-zero index vanishes in the continuum limit, unlike the
corresponding results in the commutative space.Comment: 22 pages, 8 figures, LaTeX, JHEP3.cls. v3:figures 1 and 2 improved
(all the solutions included),version published in JHE
Finite-matrix formulation of gauge theories on a non-commutative torus with twisted boundary conditions
We present a novel finite-matrix formulation of gauge theories on a
non-commutative torus. Unlike the previous formulation based on a map from a
square matrix to a field on a discretized torus with periodic boundary
conditions, our formulation is based on the algebraic characterization of the
configuration space. This enables us to describe the twisted boundary
conditions in terms of finite matrices and hence to realize the Morita
equivalence at a fully regularized level. Matter fields in the fundamental
representation turn out to be represented by rectangular matrices for twisted
boundary conditions analogously to the matrix spherical harmonics on the fuzzy
sphere with the monopole background. The corresponding Ginsparg-Wilson Dirac
operator defines an index, which can be used to classify gauge field
configurations into topological sectors. We also perform Monte Carlo
calculations for the index as a consistency check. Our formulation is expected
to be useful for applications of non-commutative geometry to various problems
related to topological aspects of field theories and string theories.Comment: 25 pages, 2 figures v2: 2 figures added, version published in JHE
P oS(LATTICE 2007)049 Simulation Results for U 1 Gauge Theory on Non-Commutative Spaces
We present numerical results for U 1 gauge theory in 2d and 4d spaces involving a non-commutative plane. Simulations are feasible thanks to a mapping of the non-commutative plane onto a twisted matrix model. In d 2 it was a long-standing issue if Wilson loops are (partially) invariant under area-preserving diffeomorphisms. We show that non-perturbatively this invari-ance breaks, including the subgroup SL 2 R . In both cases, d 2 and d 4, we extrapolate our results to the continuum and innite volume by means of a Double Scaling Limit. In d 4 this limit leads to a phase with broken translation symmetry, which is not affected by the perturbatively known IR instability. Therefore the photon may survive in a non-commutative world. The XXV International Symposium on Lattice Field Theor