45,577 research outputs found
Entanglement entropy with localized and extended interface defects
The quantum Ising chain of length, L, which is separated into two parts by
localized or extended defects is considered at the critical point where scaling
of the interface magnetization is non-universal. We measure the entanglement
entropy between the two halves of the system in equilibrium, as well as after a
quench, when the interaction at the interface is changed for time t>0. For the
localized defect the increase of the entropy with log(L) or with log(t)
involves the same effective central charge, which is a continuous function of
the strength of the defect. On the contrary for the extended defect the
equilibrium entropy is saturated, but the non-equilibrium entropy has a
logarithmic time-dependence the prefactor of which depends on the strength of
the defect.Comment: 9 pages, 6 figure
Probabilistic Bag-Of-Hyperlinks Model for Entity Linking
Many fundamental problems in natural language processing rely on determining
what entities appear in a given text. Commonly referenced as entity linking,
this step is a fundamental component of many NLP tasks such as text
understanding, automatic summarization, semantic search or machine translation.
Name ambiguity, word polysemy, context dependencies and a heavy-tailed
distribution of entities contribute to the complexity of this problem.
We here propose a probabilistic approach that makes use of an effective
graphical model to perform collective entity disambiguation. Input mentions
(i.e.,~linkable token spans) are disambiguated jointly across an entire
document by combining a document-level prior of entity co-occurrences with
local information captured from mentions and their surrounding context. The
model is based on simple sufficient statistics extracted from data, thus
relying on few parameters to be learned.
Our method does not require extensive feature engineering, nor an expensive
training procedure. We use loopy belief propagation to perform approximate
inference. The low complexity of our model makes this step sufficiently fast
for real-time usage. We demonstrate the accuracy of our approach on a wide
range of benchmark datasets, showing that it matches, and in many cases
outperforms, existing state-of-the-art methods
Qualitative observation of reversible phase change in astrochemical ethanethiol ices using infrared spectroscopy
Here we report the first evidence for a reversible phase change in an ethanethiol ice prepared under astrochemical conditions. InfraRed (IR) spectroscopy was used to monitor the morphology of the ice using the Ssingle bondH stretching vibration, a characteristic vibration of thiol molecules. The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10 K and 130 K with subsequent loss of molecules in every phase change. Such an effect is dependent upon the original thickness of the ice. Further work on quantitative analysis is to be carried out in due course whereas here we are reporting the first results obtained
Constraining the initial temperature and shear viscosity in a hybrid hydrodynamic model of =200 GeV Au+Au collisions using pion spectra, elliptic flow, and femtoscopic radii
A new framework for evaluating hydrodynamic models of relativistic heavy ion
collisions has been developed. This framework, a Comprehesive Heavy Ion Model
Evaluation and Reporting Algorithm (CHIMERA) has been implemented by augmenting
UVH 2+1D viscous hydrodynamic model with eccentricity fluctuations,
pre-equilibrium flow, and the Ultra-relativistic Quantum Molecular Dynamic
(UrQMD) hadronic cascade. A range of initial temperatures and shear viscosity
to entropy ratios were evaluated for four initial profiles, and
scaling with and without pre-equilibrium flow. The model results
were compared to pion spectra, elliptic flow, and femtoscopic radii from 200
GeV Au+Au collisions for the 0--20% centrality range.Two sets of initial
density profiles, scaling with pre-equilibrium flow and
scaling without were shown to provide a consistent description of all three
measurements.Comment: 21 pages, 32 figures, version 3 includes additional text for
clarification, division of figures into more manageable units, and placement
of chi-squared values in tables for ease of viewin
Homological algebra for osp(1/2n)
We discuss several topics of homological algebra for the Lie superalgebra
osp(1|2n). First we focus on Bott-Kostant cohomology, which yields classical
results although the cohomology is not given by the kernel of the Kostant
quabla operator. Based on this cohomology we can derive strong
Bernstein-Gelfand-Gelfand resolutions for finite dimensional osp(1|2n)-modules.
Then we state the Bott-Borel-Weil theorem which follows immediately from the
Bott-Kostant cohomology by using the Peter-Weyl theorem for osp(1|2n). Finally
we calculate the projective dimension of irreducible and Verma modules in the
category O
Comparing Cosmic Microwave Background Datasets
To extract reliable cosmic parameters from cosmic microwave background
datasets, it is essential to show that the data are not contaminated by
residual non-cosmological signals. We describe general statistical approaches
to this problem, with an emphasis on the case in which there are two datasets
that can be checked for consistency. A first visual step is the Wiener filter
mapping from one set of data onto the pixel basis of another. For more
quantitative analyses we develop and apply both Bayesian and frequentist
techniques. We define the ``contamination parameter'' and advocate the
calculation of its probability distribution as a means of examining the
consistency of two datasets. The closely related ``probability enhancement
factor'' is shown to be a useful statistic for comparison; it is significantly
better than a number of chi-squared quantities we consider. Our methods can be
used: internally (between different subsets of a dataset) or externally
(between different experiments); for observing regions that completely overlap,
partially overlap or overlap not at all; and for observing strategies that
differ greatly.
We apply the methods to check the consistency (internal and external) of the
MSAM92, MSAM94 and Saskatoon Ring datasets. From comparing the two MSAM
datasets, we find that the most probable level of contamination is 12%, with no
contamination only 1.05 times less probable, and 100% contamination strongly
ruled out at over 2 X 10^5 times less probable. From comparing the 1992 MSAM
flight with the Saskatoon data we find the most probable level of contamination
to be 50%, with no contamination only 1.6 times less probable and 100%
contamination 13 times less probable. [Truncated]Comment: LaTeX, 16 pages which include 16 figures, submitted to Phys. Rev.
Implementing Unitarity in Perturbation Theory
Unitarity cannot be perserved order by order in ordinary perturbation theory
because the constraint UU^\dagger=\1 is nonlinear. However, the corresponding
constraint for , being , is linear so it can be
maintained in every order in a perturbative expansion of . The perturbative
expansion of may be considered as a non-abelian generalization of the
linked-cluster expansion in probability theory and in statistical mechanics,
and possesses similar advantages resulting from separating the short-range
correlations from long-range effects. This point is illustrated in two QCD
examples, in which delicate cancellations encountered in summing Feynman
diagrams of are avoided when they are calculated via the perturbative expansion
of . Applications to other problems are briefly discussed.Comment: to appear in Phys. Rev.
Effect of gauge boson mass on chiral symmetry breaking in QED
In three-dimensional quantum electrodynamics (QED) with massive gauge
boson, we investigate the Dyson-Schwinger equation for the fermion self-energy
in the Landau gauge and find that chiral symmetry breaking (CSB) occurs when
the gauge boson mass is smaller than a finite critical value
but is suppressed when . We further show that the critical
value does not qualitatively change after considering higher order
corrections from the wave function renormalization and vertex function. Based
on the relation between CSB and the gauge boson mass , we give a field
theoretical description of the competing antiferromagnetic and superconducting
orders and, in particular, the coexistence of these two orders in high
temperature superconductors. When the gauge boson mass is generated via
instanton effect in a compact QED of massless fermions, our result shows
that CSB coexists with instanton effect in a wide region of , which can be
used to study the confinement-deconfinement phase transition.Comment: 34 pagess, 2 figure
Veneziano Ghost Versus Isospin Breaking
It is argued that an account for the Veneziano ghost pole, appearing in
resolving the U(1) problem, is necessary for understanding an isospin violation
in the system. By virtue of a perturbative expansion
around the ( ) symmetric Veneziano solution, we
find that the ghost considerably suppresses isospin breaking gluon and s-quark
matrix elements. We speculate further on a few cases where the proposed
mechanism can play an essential role. We discuss the isospin violation in
meson-nucleon couplings and its relevance to the problem of charge asymmetric
nuclear forces and possible breaking of the Bjorken sum rule. It is shown that
the ghost pole could yield the isospin violation of order 2 \% for the couplings and 20 \% for the
Bjorken sum rule.Comment: 16 pages , Preprint TAUP-2127-9
H_c_3 for a thin-film superconductor with a ferromagnetic dot
We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large
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