867 research outputs found
Fluctuation effects in disordered Peierls systems
We review the density of states and related quantities of quasi
one-dimensional disordered Peierls systems in which fluctuation effects of a
backscattering potential play a crucial role. The low-energy behavior of
non-interacting fermions which are subject to a static random backscattering
potential will be described by the fluctuating gap model (FGM). Recently, the
FGM has also been used to explain the pseudogap phenomenon in high-
superconductors. After an elementary introduction to the FGM in the context of
commensurate and incommensurate Peierls chains, we develop a non-perturbative
method which allows for a simultaneous calculation of the density of states
(DOS) and the inverse localization length. First, we recover all known results
in the limits of zero and infinite correlation lengths of the random potential.
Then, we attack the problem of finite correlation lengths. While a complex
order parameter, which describes incommensurate Peierls chains, leads to a
suppression of the DOS, i.e. a pseudogap, the DOS exhibits a singularity at the
Fermi energy if the order parameter is real and therefore refers to a
commensurate system. We confirm these results by calculating the DOS and the
inverse localization length for finite correlation lengths and Gaussian
statistics of the backscattering potential with unprecedented accuracy
numerically. Finally, we consider the case of classical phase fluctuations
which apply to low temperatures where amplitude fluctuations are frozen out. In
this physically important regime, which is also characterized by finite
correlation lengths, we present analytic results for the DOS, the inverse
localization length, the specific heat, and the Pauli susceptibility.Comment: 60 pages, 16 figure
Uniqueness and nonuniqueness of the stationary black holes in 5D Einstein-Maxwell and Einstein-Maxwell-dilaton gravity
In the present paper we investigate the general problem of uniqueness of the
stationary black solutions in 5D Einstein-Maxwell-dilaton gravity with
arbitrary dilaton coupling parameter containing the Einstein-Maxwell gravity as
a particular case. We formulate and prove uniqueness theorems classifying the
stationary black hole solutions in terms of their interval structure, electric
and magnetic charges and the magnetic fluxes. The proofs are based on the
nonpositivity of the Riemann curvature operator on the space of the potentials
which imposes restrictions on the dilaton coupling parameter.Comment: 21 pages, LaTe
Batalin-Vilkovisky formalism in perturbative algebraic quantum field theory
On the basis of a thorough discussion of the Batalin-Vilkovisky formalism for
classical field theory presented in our previous publication, we construct in
this paper the Batalin-Vilkovisky complex in perturbatively renormalized
quantum field theory. The crucial technical ingredient is a proof that the
renormalized time-ordered product is equivalent to the pointwise product of
classical field theory. The renormalized Batalin-Vilkovisky algebra is then the
classical algebra but written in terms of the time-ordered product, together
with an operator which replaces the ill defined graded Laplacian of the
unrenormalized theory. We identify it with the anomaly term of the anomalous
Master Ward Identity of Brennecke and D\"utsch. Contrary to other approaches we
do not refer to the path integral formalism and do not need to use
regularizations in intermediate steps.Comment: 34 page
Perturbative Construction of Models of Algebraic Quantum Field Theory
We review the construction of models of algebraic quantum field theory by
renormalized perturbation theory.Comment: 38 page
On leading order gravitational backreactions in de Sitter spacetime
Backreactions are considered in a de Sitter spacetime whose cosmological
constant is generated by the potential of scalar field. The leading order
gravitational effect of nonlinear matter fluctuations is analyzed and it is
found that the initial value problem for the perturbed Einstein equations
possesses linearization instabilities. We show that these linearization
instabilities can be avoided by assuming strict de Sitter invariance of the
quantum states of the linearized fluctuations. We furthermore show that quantum
anomalies do not block the invariance requirement. This invariance constraint
applies to the entire spectrum of states, from the vacuum to the excited states
(should they exist), and is in that sense much stronger than the usual Poincare
invariance requirement of the Minkowski vacuum alone. Thus to leading order in
their effect on the gravitational field, the quantum states of the matter and
metric fluctuations must be de Sitter invariant.Comment: 12 pages, no figures, typos corrected and some clarifying comments
added, version accepted by Phys. Rev.
Cosmological Perturbation Theory in Slow-Roll Spacetimes
We present a gauge invariant argument that a nonlocal measure of second-order
metric and matter perturbations dominate that of linear fluctuations in its
effect on the gravitational field in 'slow-rolling' spacetimes.Comment: Version accepted by PRL (however, with correct non PRL format for
arxiv posting). Clarified and expande
Information-based cues at point of choice to change selection and consumption of food, alcohol and tobacco products: a systematic review
Background:
Reducing harmful consumption of food, alcohol, and tobacco products would prevent many cancers, diabetes and cardiovascular disease. Placing information-based cues in the environments in which we select and consume these products has the potential to contribute to changing these behaviours.
Methods:
In this review, information-based cues are defined as those which comprise any combination of words, symbols, numbers or pictures that convey information about a product or its use. We specifically exclude cues which are located on the products themselves. We conducted a systematic review of randomised, cluster- randomised, and non-randomised controlled trials to assess the impact of such cues on selection and consumption. Thirteen studies met the inclusion criteria, of which 12 targeted food (most commonly fruit and vegetables), one targeted alcohol sales, and none targeted tobacco products.
Results:
Ten studies reported statistically significant effects on some or all of the targeted products, although studies were insufficiently homogenous to justify meta-analysis. Existing evidence suggests information-based cues can influence selection and consumption of food and alcohol products, although significant uncertainty remains.
Conclusions:
The current evidence base is limited both in quality and quantity, with relatively few, heterogeneous studies at unclear or high risk of bias. Additional, more rigorously conducted studies are warranted to better estimate the potential for these interventions to change selection and consumption of food, alcohol and tobacco products.
Trial registration:
PROSPERO. 2016;CRD42016051884
All Vacuum Near-Horizon Geometries in -dimensions with Commuting Rotational Symmetries
We explicitly construct all stationary, non-static, extremal near horizon
geometries in dimensions that satisfy the vacuum Einstein equations, and
that have commuting rotational symmetries. Our work generalizes
[arXiv:0806.2051] by Kunduri and Lucietti, where such a classification had been
given in . But our method is different from theirs and relies on a
matrix formulation of the Einstein equations. Unlike their method, this matrix
formulation works for any dimension. The metrics that we find come in three
families, with horizon topology , or ,
or quotients thereof. Our metrics depend on two discrete parameters specifying
the topology type, as well as continuous parameters. Not all of
our metrics in seem to arise as the near horizon limits of known
black hole solutions.Comment: 22 pages, Latex, no figures, title changed, references added,
discussion of the parameters specifying solutions corrected, amended to match
published versio
Changing Human Behavior to Prevent Disease: The Importance of Targeting Automatic Processes
http://dx.doi.org/10.1126/science.122691
Local Thermal Equilibrium in Quantum Field Theory on Flat and Curved Spacetimes
The existence of local thermal equilibrium (LTE) states for quantum field
theory in the sense of Buchholz, Ojima and Roos is discussed in a
model-independent setting. It is shown that for spaces of finitely many
independent thermal observables there always exist states which are in LTE in
any compact region of Minkowski spacetime. Furthermore, LTE states in curved
spacetime are discussed and it is observed that the original definition of LTE
on curved backgrounds given by Buchholz and Schlemmer needs to be modified.
Under an assumption related to certain unboundedness properties of the
pointlike thermal observables, existence of states which are in LTE at a given
point in curved spacetime is established. The assumption is discussed for the
sets of thermal observables for the free scalar field considered by Schlemmer
and Verch.Comment: 16 pages, some minor changes and clarifications; section 4 has been
shortened as some unnecessary constructions have been remove
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