1,062 research outputs found
Effective Potential on Fuzzy Sphere
The effective potential of quantized scalar field on fuzzy sphere is
evaluated to the two-loop level. We see that one-loop potential behaves like
that in the commutative sphere and the Coleman-Weinberg mechanism of the
radiatively symmetry breaking could be also shown in the fuzzy sphere system.
In the two-loop level, we use the heavy-mass approximation and the
high-temperature approximation to perform the evaluations. The results show
that both of the planar and nonplanar Feynman diagrams have inclinations to
restore the symmetry breaking in the tree level. However, the contributions
from planar diagrams will dominate over those from nonplanar diagrams by a
factor N^2. Thus, at heavy-mass limit or high-temperature system the quantum
field on the fuzzy sphere will behave like those on the commutative sphere. We
also see that there is a drastic reduction of the degrees of freedom in the
nonplanar diagrams when the particle wavelength is smaller than the
noncommutativity scale.Comment: Latex 18 pages, some typos correcte
Cosmological and Black Hole Spacetimes in Twisted Noncommutative Gravity
We derive noncommutative Einstein equations for abelian twists and their
solutions in consistently symmetry reduced sectors, corresponding to twisted
FRW cosmology and Schwarzschild black holes. While some of these solutions must
be rejected as models for physical spacetimes because they contradict
observations, we find also solutions that can be made compatible with low
energy phenomenology, while exhibiting strong noncommutativity at very short
distances and early times.Comment: LaTeX 12 pages, JHEP.st
An interleaved sampling scheme for the characterization of single qubit dynamics
In this paper, we demonstrate that interleaved sampling techniques can be
used to characterize the Hamiltonian of a qubit and its environmental
decoherence rate. The technique offers a significant advantage in terms of the
number of measurements that are required to characterize a qubit. When compared
to the standard Nyquist-Shannon sampling rate, the saving in the total
measurement time for the interleaved method is approximately proportional to
the ratio of the sample rates.Comment: 9 pages, 4 figure
Interferon-λ restricts West Nile virus neuroinvasion by tightening the blood-brain barrier
Although interferon-λ [also known as type III interferon or interleukin-28 (IL-28)/IL-29] restricts infection by several viruses, its inhibitory mechanism has remained uncertain. We used recombinant interferon-λ and mice lacking the interferon-λ receptor (IFNLR1) to evaluate the effect of interferon-λ on infection with West Nile virus, an encephalitic flavivirus. Cell culture studies in mouse keratinocytes and dendritic cells showed no direct antiviral effect of exogenous interferon-λ, even though expression of interferon-stimulated genes was induced. We observed no differences in West Nile virus burden between wild-type and Ifnlr1-/- mice in the draining lymph nodes, spleen, or blood. We detected increased West Nile virus infection in the brain and spinal cord of Ifnlr1-/- mice, yet this was not associated with a direct antiviral effect in mouse neurons. Instead, we observed an increase in blood-brain barrier permeability in Ifnlr1-/- mice. Treatment of mice with pegylated interferon-λ2 resulted in decreased blood-brain barrier permeability, reduced West Nile virus infection in the brain without affecting viremia, and improved survival against lethal virus challenge. An in vitro model of the blood-brain barrier showed that interferon-λ signaling in mouse brain microvascular endothelial cells increased transendothelial electrical resistance, decreased virus movement across the barrier, and modulated tight junction protein localization in a protein synthesis- and signal transducer and activator of transcription 1 (STAT1)-independent manner. Our data establish an indirect antiviral function of interferon-λ in which noncanonical signaling through IFNLR1 tightens the blood-brain barrier and restricts viral neuroinvasion and pathogenesis
Lanthanides in granulometric fractions of Mediterranean soils. Can they be used as fingerprints of provenance?
Highlights
Are lanthanides from fine sand and clay genetically related to the geological materials?
Lanthanide concentrations of fine sand and clay fit chronofunctions
Pearson's r of lanthanide couples decreases when separation increases in the periodic table
Free forms of clay are scavengers of lanthanides and concentrate HREE and ceriumSample preparation and chemical analysis were conducted by
Emma Humphreys-Williams and Stanislav Strekopytov (Imaging
and Analysis Centre, Natural History Museum, London, UK). This
work was supported by a grant from Ministerio de Economía, Industria y Competitividad de España (‘Tipologías de Suelos Mediterráneos versus Cuarzo. En la frontera del conocimiento edafogenético’; Ref. CGL2016-80308-P). The authors thank Professor
Margaret A. Oliver, an anonymous editor and two anonymous
reviewers for helpful comments and suggestions that improved the
final manuscript. We also thank Robert Abrahams (Bsc) for revising
the English language.There is geochemical interest in the lanthanides because they behave like a group that is closely related to the parent materials during surface processes, although they also undergo fractionation as a result of supergene dynamics. We analysed lanthanide concentrations (ICPms) in the granulometric fractions fine sand, clay and free forms of clay (FFclay‐CDB and FFclay‐Ox: extracted with citrate‐dithionite‐sodium bicarbonate and with ammonium oxalate, respectively) from a soil chronosequence of Mediterranean soils. There was a relative enrichment of heavy rare earth elements (HREE) in the clay fraction and its free forms with respect to fine sand. The clay free forms behaved as scavengers of lanthanides, and oxidative scavenging of cerium (Ce) in FFclay‐CDB was also detected. Lanthanide concentrations (lanthanum to gadolinium in fine sand; terbium to lutetium in clay) varied with soil age, and chronofunctions were established. There was a strong positive collinearity between most of the lanthanide concentrations. Furthermore, the value of the correlation index (Pearson's r ) of the concentrations between couples of lanthanides (r CLC) decreased significantly with increasing separation between the elements in the periodic table; this has never been described in soils. Several geochemical properties and indices in the fine sand and clay soil fractions and in the geological materials of the Guadalquivir catchment showed, on the one hand, a genetic relation between them all, enabling the lanthanides to be used as fingerprints of provenance; on the other hand, fractionation between fine sand and clay showed these are actively involved in soil lanthanide dynamics.Secretaría de Estado de Investigación, Desarrollo e Innovación. Grant Number: CGL2016‐80308‐
Nonperturbative studies of fuzzy spheres in a matrix model with the Chern-Simons term
Fuzzy spheres appear as classical solutions in a matrix model obtained via
dimensional reduction of 3-dimensional Yang-Mills theory with the Chern-Simons
term. Well-defined perturbative expansion around these solutions can be
formulated even for finite matrix size, and in the case of coincident fuzzy
spheres it gives rise to a regularized U() gauge theory on a noncommutative
geometry. Here we study the matrix model nonperturbatively by Monte Carlo
simulation. The system undergoes a first order phase transition as we change
the coefficient () of the Chern-Simons term. In the small
phase, the large properties of the system are qualitatively the same as in
the pure Yang-Mills model (), whereas in the large phase a
single fuzzy sphere emerges dynamically. Various `multi fuzzy spheres' are
observed as meta-stable states, and we argue in particular that the
coincident fuzzy spheres cannot be realized as the true vacuum in this model
even in the large limit. We also perform one-loop calculations of various
observables for arbitrary including . Comparison with our Monte Carlo
data suggests that higher order corrections are suppressed in the large
limit.Comment: Latex 37 pages, 13 figures, discussion on instabilities refined,
references added, typo corrected, the final version to appear in JHE
Stability of Repulsive Bose-Einstein Condensates in a Periodic Potential
The cubic nonlinear Schr\"odinger equation with repulsive nonlinearity and an
elliptic function potential models a quasi-one-dimensional repulsive dilute gas
Bose-Einstein condensate trapped in a standing light wave. New families of
stationary solutions are presented. Some of these solutions have neither an
analog in the linear Schr\"odinger equation nor in the integrable nonlinear
Schr\"odinger equation. Their stability is examined using analytic and
numerical methods. All trivial-phase stable solutions are deformations of the
ground state of the linear Schr\"odinger equation. Our results show that a
large number of condensed atoms is sufficient to form a stable, periodic
condensate. Physically, this implies stability of states near the Thomas-Fermi
limit.Comment: 12 pages, 17 figure
Universal flow diagram for the magnetoconductance in disordered GaAs layers
The temperature driven flow lines of the diagonal and Hall magnetoconductance
data (G_{xx},G_{xy}) are studied in heavily Si-doped, disordered GaAs layers
with different thicknesses. The flow lines are quantitatively well described by
a recent universal scaling theory developed for the case of duality symmetry.
The separatrix G_{xy}=1 (in units e^2/h) separates an insulating state from a
spin-degenerate quantum Hall effect (QHE) state. The merging into the insulator
or the QHE state at low temperatures happens along a semicircle separatrix
G_{xx}^2+(G_{xy}-1)^2=1 which is divided by an unstable fixed point at
(G_{xx},G_{xy})=(1,1).Comment: 10 pages, 5 figures, submitted to Phys. Rev. Let
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
On the construction of a geometric invariant measuring the deviation from Kerr data
This article contains a detailed and rigorous proof of the construction of a
geometric invariant for initial data sets for the Einstein vacuum field
equations. This geometric invariant vanishes if and only if the initial data
set corresponds to data for the Kerr spacetime, and thus, it characterises this
type of data. The construction presented is valid for boosted and non-boosted
initial data sets which are, in a sense, asymptotically Schwarzschildean. As a
preliminary step to the construction of the geometric invariant, an analysis of
a characterisation of the Kerr spacetime in terms of Killing spinors is carried
out. A space spinor split of the (spacetime) Killing spinor equation is
performed, to obtain a set of three conditions ensuring the existence of a
Killing spinor of the development of the initial data set. In order to
construct the geometric invariant, we introduce the notion of approximate
Killing spinors. These spinors are symmetric valence 2 spinors intrinsic to the
initial hypersurface and satisfy a certain second order elliptic equation
---the approximate Killing spinor equation. This equation arises as the
Euler-Lagrange equation of a non-negative integral functional. This functional
constitutes part of our geometric invariant ---however, the whole functional
does not come from a variational principle. The asymptotic behaviour of
solutions to the approximate Killing spinor equation is studied and an
existence theorem is presented.Comment: 36 pages. Updated references. Technical details correcte
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