72 research outputs found
Optical excitations in a one-dimensional Mott insulator
The density-matrix renormalization-group (DMRG) method is used to investigate
optical excitations in the Mott insulating phase of a one-dimensional extended
Hubbard model. The linear optical conductivity is calculated using the
dynamical DMRG method and the nature of the lowest optically excited states is
investigated using a symmetrized DMRG approach. The numerical calculations
agree perfectly with field-theoretical predictions for a small Mott gap and
analytical results for a large Mott gap obtained with a strong-coupling
analysis. Is is shown that four types of optical excitations exist in this Mott
insulator: pairs of unbound charge excitations, excitons, excitonic strings,
and charge-density-wave (CDW) droplets. Each type of excitations dominates the
low-energy optical spectrum in some region of the interaction parameter space
and corresponds to distinct spectral features: a continuum starting at the Mott
gap (unbound charge excitations), a single peak or several isolated peaks below
the Mott gap (excitons and excitonic strings, respectively), and a continuum
below the Mott gap (CDW droplets).Comment: 12 pages (REVTEX 4), 12 figures (in 14 eps files), 1 tabl
Complete solutions to the metric of spherically collapsing dust in an expanding spacetime with a cosmological constant
We present semi-analytical solutions to the background equations describing
the Lema\^itre-Tolman-Bondi (LTB) metric as well as the homogeneous Friedmann
equations, in the presence of dust, curvature and a cosmological constant
Lambda. For none of the presented solutions any numerical integration has to be
performed. All presented solutions are given for expanding and collapsing
phases, preserving continuity in time and radius. Hence, these solutions
describe the complete space time of a collapsing spherical object in an
expanding universe. In the appendix we present for completeness a solution of
the Friedmann equations in the additional presence of radiation, only valid for
the Robertson-Walker metric.Comment: 23 pages, one figure. Numerical module for evaluation of the
solutions released at
http://web.physik.rwth-aachen.de/download/valkenburg/ColLambda/ Matches
published version, published under Open Access. Note change of titl
Brane World Effective Action at Low Energies and AdS/CFT Correspondence
A low energy iteration scheme to study nonlinear gravity in the brane world
is developed. As a result, we obtain the brane world effective action at low
energies. The relation between the geometrical approach and the approach using
the AdS/CFT correspondence is also clarified. In particular, we find
generalized dark radiation as homogeneous solutions in our iteration scheme.
Moreover, the precise correspondence between the bulk geometry and the brane
effective action is established, which gives a holographic view of the brane
world.Comment: Revtex4, 12 pages, references added. Version accepted for publicaton
in Phys. Rev.
Open data from the third observing run of LIGO, Virgo, KAGRA, and GEO
The global network of gravitational-wave observatories now includes five detectors, namely LIGO Hanford, LIGO Livingston, Virgo, KAGRA, and GEO 600. These detectors collected data during their third observing run, O3, composed of three phases: O3a starting in 2019 April and lasting six months, O3b starting in 2019 November and lasting five months, and O3GK starting in 2020 April and lasting two weeks. In this paper we describe these data and various other science products that can be freely accessed through the Gravitational Wave Open Science Center at https://gwosc.org. The main data set, consisting of the gravitational-wave strain time series that contains the astrophysical signals, is released together with supporting data useful for their analysis and documentation, tutorials, as well as analysis software packages
Computational Characterization of Micro- to Macroscopic Mechanical Behavior and Damage of Polymers Containing Second-Phase Particles
An NMR study of the interaction of purine and pyrimidine derivatives with acridine orange
The Continuous π-Calculus: A Process Algebra for Biochemical Modelling
Abstract. We introduce the continuous π-calculus, a process algebra for modelling behaviour and variation in molecular systems. Key features of the language are: its expressive succinctness; support for diverse interaction between agents via a flexible network of molecular affinities; and operational semantics for a continuous space of processes. This compositional semantics also gives a modular way to generate conventional differential equations for system behaviour over time. We illustrate these features with a model of an existing biological system, a simple oscillatory pathway in cyanobacteria. We then discuss future research directions, in particular routes to applying the calculus in the study of evolutionary properties of biochemical pathways.
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