2,106 research outputs found
A solution to the anisotropy problem in bouncing cosmologies
Bouncing cosmologies are often proposed as alternatives to standard inflation
for the explanation of the homogeneity and flatness of the universe. In such
scenarios, the present cosmological expansion is preceded by a contraction
phase. However, during the contraction, in general the anisotropy of the
universe grows and eventually leads to a chaotic mixmaster behavior. This would
either be hard to reconcile with observations or even lead to a singularity
instead of the bounce. In order to preserve a smooth and isotropic bounce, the
source for the contraction must have a super-stiff equation of state with
. In this letter we propose a new mechanism to solve the anisotropy
problem for any low-energy value of by arguing that high energy physics
leads to a modification of the equation of state, with the introduction of
non-linear terms. In such a scenario, the anisotropy is strongly suppressed
during the high energy phase, allowing for a graceful isotropic bounce, even
when the low-energy value of is smaller than unity.Comment: 9 pages, accepted for publication in JCA
Scalar fluctuations in dilatonic brane-worlds
We derive and solve the full set of scalar perturbation equations for a class
of five-dimensional brane--world solutions, with a dilaton scalar field coupled
to the bulk cosmological constant and to a 3-brane. The spectrum contains one
localized massless scalar mode, to be interpreted as an effective dilaton on
the brane, inducing long--range scalar interactions. Two massive scalar modes
yield corrections to Newton's law at short distances, which persist even in the
limit of vanishing dilaton (namely, in the standard Randall--Sundrum
configuration).Comment: 10 pages. Talk presented by V. Bozza at COSMO-01 conference,
Rovaniemi, 200
Assisting pre-big bang phenomenology through short-lived axions
We present the results of a detailed study of how isocurvature axion
fluctuations are converted into adiabatic metric perturbations through axion
decay, and discuss the constraints on the parameters of pre-big bang cosmology
needed for consistency with present CMB-anisotropy data. The large-scale
normalization of temperature fluctuations has a non-trivial dependence both on
the mass and on the initial value of the axion. In the simplest, minimal models
of pre-big bang inflation, consistency with the COBE normalization requires a
slightly tilted (blue) spectrum, while a strictly scale-invariant spectrum
requires mild modifications of the minimal backgrounds at large curvature
and/or string coupling.Comment: 14 pages, latex, 1 figure included using epsfig. A few typos
corrected, two references added, the figure slightly improved. To appear in
Phys. Lett.
Constraints on pre-big bang parameter space from CMBR anisotropies
The so-called curvaton mechanism --a way to convert isocurvature
perturbations into adiabatic ones-- is investigated both analytically and
numerically in a pre-big bang scenario where the role of the curvaton is played
by a sufficiently massive Kalb--Ramond axion of superstring theory. When
combined with observations of CMBR anisotropies at large and moderate angular
scales, the present analysis allows us to constrain quite considerably the
parameter space of the model: in particular, the initial displacement of the
axion from the minimum of its potential and the rate of evolution of the
compactification volume during pre-big bang inflation. The combination of
theoretical and experimental constraints favours a slightly blue spectrum of
scalar perturbations, and/or a value of the string scale in the vicinity of the
SUSY-GUT scale.Comment: 63 pages in Latex style with 14 figures include
Properties of Planetary Caustics in Gravitational Microlensing
Although some of the properties of the caustics in planetary microlensing
have been known, our understanding of them is mostly from scattered information
based on numerical approaches. In this paper, we conduct a comprehensive and
analytic analysis of the properties of the planetary caustics, which are one of
the two sets of caustics in planetary microlensing, those located away from the
central star. Under the perturbative approximation, we derive analytic
expressions for the location, size, and shape of the planetary caustic as a
function of the star-planet separation and the planet/star mass ratio. Based on
these expressions combined with those for the central caustic, which is the
other set of caustics located close to the central star, we compare the
similarities and differences between the planetary and central caustics. We
also present the expressions for the size ratio between the two types of
caustics and for the condition of the merging of the two types of caustics.
These analytic expressions will be useful in understanding the dependence of
the planetary lensing behavior on the planet parameters and thus in
interpreting the planetary lensing signalsComment: total 6 pages, including 6 figures, ApJ, submitte
Analysis of Microlensing Light Curves Induced by Multiple-Planet Systems
To maximize the number of planet detections by increasing efficiency, current
microlensing follow-up observation experiments are focusing on
high-magnification events to search for planet-induced perturbations near the
peak of lensing light curves. It was known that by monitoring
high-magnification events, it is possible to detect multiplicity signatures of
planetary systems. However, it was believed that the interpretation of the
signals and the characterization of the detected multiple-planet systems would
be difficult due to the complexity of the magnification pattern in the central
region combined with the large number of lensing parameters required to model
multiple-planet systems. In this paper, we demonstrate that in many cases the
central planetary perturbations induced by multiple planets can be well
approximated by the superposition of the single planetary perturbations where
the individual planet-primary pairs act as independent binary lens systems
(binary superposition). The validity of the binary-superposition approximation
implies that the analysis of perturbations induced by multiple planets can be
greatly simplified because the anomalies produced by the individual planet
components can be investigated separately by using relatively much simpler
single-planetary analysis, and thus enables better characterization of these
systems.Comment: Manuscript with high-resolution figures are available at
http://astroph.chungbuk.ac.kr/~cheongho/preprint.htm
Analytic Kerr black hole lensing for equatorial observers in the strong deflection limit
In this paper we present an analytical treatment of gravitational lensing by
Kerr black holes in the limit of very large deflection angles, restricting to
observers in the equatorial plane. We accomplish our objective starting from
the Schwarzschild black hole and adding corrections up to second order in the
black hole spin. This is sufficient to provide a full description of all
caustics and the inversion of lens mapping for sources near them. On the basis
of these formulae we argue that relativistic images of Low Mass X-ray Binaries
around Sgr A* are very likely to be seen by future X-ray interferometry
missions.Comment: 19 pages, 9 figures, published on Phys. Rev.
KINERJA PT. BANK ACEH KANTOR PUSAT OPERASIONAL
PT. Bank Aceh adalah bank milik Pemerintah Aceh yaitu lembaga keuangan daerah untuk membantu dan mendorong pertumbuhan ekonomi Aceh. Penelitian ini bertujuan mengetahui budaya organisasi, kompetensi, dan kepemimpinan terhadap kinerja karyawan dan dampaknya kinerja PT. Bank Aceh.Penelitian ini dilakukan pada PT. Bank Aceh Kantor Pusat Operasional Banda Aceh dengan 135 orang karyawan sebagai responden, alat ukur yang digunakan adalah kuesioner dengan pilihan rank 5 skala likert, data diuji dengan validitas dan reliabilitas, dianalisis dengan analisis Structural Equation Modeling.Hasil penelitian menunjukkan bahwa semua variabel yang diteliti valid dan reliabel, identifikasi variabel budaya organisasi, variabel kompetensi dan variabel kepemimpinan pada nilai rata-rata skore setuju, variabel intervening kinerja karyawan dan variabel kinerja PT. Bank Aceh juga dipersepsikan pada skor setuju. Dari hasil uji measurement model melalui loading factor budaya organisasi, variabel kompetensi dan variabel kepemimpinan telah memenuhi kriteria.Uji hipotesis didapati adanya pengaruh variabel independen budaya organisasi dengan variabel kinerja PT. Bank Aceh. Hipotesis lainnya ditolak karena pengaruhnya independen tidak signifikan terhadap kinerja PT. Bank Aceh.Disimpulkan bahwa terdapat pengaruh langsung antara budaya organisasi terhadap kinerja PT. Bank Aceh, disarankan manajemen PT.Bank Aceh harus mengefektifkan kompetensi dan kepemimpinan
Strong Gravitational Lensing by Sgr A*
In recent years, there has been increasing recognition of the potential of
the galactic center as a probe of general relativity in the strong field. There
is almost certainly a black hole at Sgr A* in the galactic center, and this
would allow us the opportunity to probe dynamics near the exterior of the black
hole. In the last decade, there has been research into extreme gravitational
lensing in the galactic center. Unlike in most applications of gravitational
lensing, where the bending angle is of the order of several arc seconds, very
large bending angles are possible for light that closely approaches a black
hole. Photons may even loop multiple times around a black hole before reaching
the observer. There have been many proposals to use light's close approach to
the black hole as a probe of the black hole metric. Of particular interest is
the property of light lensed by the S stars orbiting in the galactic center.
This paper will review some of the attempts made to study extreme lensing as
well as extend the analysis of lensing by S stars. In particular, we are
interested in the effect of a Reissner-Nordstrom like 1/r^2 term in the metric
and how this would affect the properties of relativistic images.Comment: 13 pages, 9 figures. Submitted as invited review article for the GR19
issue of CQ
- âŠ