16,416 research outputs found
Multimode switching induced by a transverse field planar magnetic nanowires
We report how transverse fields affect the axial field needed to "inject" domain walls from a large Permalloy (Ni80Fe20) pad into planar nanowires of width 184 nm, 303 nm, 321 nm, and 537 nm fabricated by electron beam lithography. For the narrowest wire, different switching fields are observed under the same transverse field conditions, indicating that more than one mode or state for the domain walls may exist. In contrast, in the widest wires a transverse field causes each reversal event to occur in two stages. The different response may be attributed to the magnetostatic energy differences of domain walls in wires of different widths
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
Multiplicative renormalizability of gluon and ghost propagators in QCD
We reformulate the coupled set of continuum equations for the renormalized
gluon and ghost propagators in QCD, such that the multiplicative
renormalizability of the solutions is manifest, independently of the specific
form of full vertices and renormalization constants. In the Landau gauge, the
equations are free of renormalization constants, and the renormalization point
dependence enters only through the renormalized coupling and the renormalized
propagator functions. The structure of the equations enables us to devise novel
truncations with solutions that are multiplicatively renormalizable and agree
with the leading order perturbative results. We show that, for infrared power
law behaved propagators, the leading infrared behavior of the gluon equation is
not solely determined by the ghost loop, as concluded in previous studies, but
that the gluon loop, the three-gluon loop, the four-gluon loop, and even
massless quarks also contribute to the infrared analysis. In our new Landau
gauge truncation, the combination of gluon and ghost loop contributions seems
to reject infrared power law solutions, but massless quark loops illustrate how
additional contributions to the gluon vacuum polarization could reinstate these
solutions. Moreover, a schematic study of the three-gluon and four-gluon loops
shows that they too need to be considered in more detail before a definite
conclusion about the existence of infrared power behaved gluon and ghost
propagators can be reached.Comment: 13 pages, 1 figure, submitted to Phys. Rev.
Antimatter, Lorentz Symmetry, and Gravity
A brief introduction to the Standard-Model Extension (SME) approach to
testing CPT and Lorentz symmetry is provided. Recent proposals for tests with
antimatter are summarized, including gravitational and spectroscopic tests.Comment: Presented at the 12th International Conference on Low Energy
Antiproton Physics, Kanazawa Japan, March 6-11, 2016, Accepted for
publication in JPS Conference Proceeding
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Functional Imaging of the Outer Retinal Complex using High Fidelity Imaging Retinal Densitometry
We describe a new technique, high fidelity Imaging Retinal Densitometry (IRD), which probes the functional integrity of the outer retinal complex. We demonstrate the ability of the technique to map visual pigment optical density and synthesis rates in eyes with and without macular disease. A multispectral retinal imaging device obtained precise measurements of retinal reflectance over space and time. Data obtained from healthy controls and 5 patients with intermediate AMD, before and after photopigment bleaching, were used to quantify visual pigment metrics. Heat maps were plotted to summarise the topography of rod and cone pigment kinetics and descriptive statistics conducted to highlight differences between those with and without AMD. Rod and cone visual pigment synthesis rates in those with AMD (v = 0.043 SD 0.019 min-1 and v = 0.119 SD 0.046 min-1, respectively) were approximately half those observed in healthy controls (v = 0.079 SD 0.024 min-1 for rods and v = 0.206 SD 0.069 min-1 for cones). By mapping visual pigment kinetics across the central retina, high fidelity IRD provides a unique insight into outer retinal complex function. This new technique will improve the phenotypic characterisation, diagnosis and treatment monitoring of various ocular pathologies, including AMD
Spontaneous Chiral-Symmetry Breaking in Three-Dimensional QED with a Chern--Simons Term
In three-dimensional QED with a Chern--Simons term we study the phase
structure associated with chiral-symmetry breaking in the framework of the
Schwinger--Dyson equation. We give detailed analyses on the analytical and
numerical solutions for the Schwinger--Dyson equation of the fermion
propagator, where the nonlocal gauge-fixing procedure is adopted to avoid
wave-function renormalization for the fermion. In the absence of the
Chern--Simons term, there exists a finite critical number of four-component
fermion flavors, at which a continuous (infinite-order) chiral phase transition
takes place and below which the chiral symmetry is spontaneously broken. In the
presence of the Chern--Simons term, we find that the spontaneous
chiral-symmetry-breaking transition continues to exist, but the type of phase
transition turns into a discontinuous first-order transition. A simple
stability argument is given based on the effective potential, whose stationary
point gives the solution of the Schwinger-Dyson equation.Comment: 34 pages, revtex, with 9 postscriptfigures appended (uuencoded
Verifying the Kugo-Ojima Confinement Criterion in Landau Gauge Yang-Mills Theory
Expanding the Landau gauge gluon and ghost two-point functions in a power
series we investigate their infrared behavior. The corresponding powers are
constrained through the ghost Dyson-Schwinger equation by exploiting
multiplicative renormalizability. Without recourse to any specific truncation
we demonstrate that the infrared powers of the gluon and ghost propagators are
uniquely related to each other. Constraints for these powers are derived, and
the resulting infrared enhancement of the ghost propagator signals that the
Kugo-Ojima confinement criterion is fulfilled in Landau gauge Yang-Mills
theory.Comment: 4 pages, no figures; version to be published in Physical Review
Letter
Regularization of the Roy Equations with a Smooth Cut-Off
The Roy equations for ππ scattering are combined with unitarity to give a nonlinear system of equations for the determination of the low‐energy amplitudes. A Hölder continuous interpolation between the input high‐energy absorptive parts and the output low‐energy absorptive parts is implemented; and the resultant singular equations are regularized by means of an effective inelastic N/D method. If the scattering lengths, the CDD parameters, and the high‐energy absorptive parts satisfy certain constraints, then there exists a locally unique solution of the system
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