54 research outputs found
Development of a Direct Fabrication Technique for Full-Shell X-Ray Optics
Future astrophysical missions will require fabrication technology capable of producing high angular resolution x-ray optics. A full-shell direct fabrication approach using modern robotic polishing machines has the potential for producing high resolution, light-weight and affordable x-ray mirrors that can be nested to produce large collecting area. This approach to mirror fabrication, based on the use of the metal substrates coated with nickel phosphorous alloy, is being pursued at MSFC. The design of the polishing fixtures for the direct fabrication, the surface figure metrology techniques used and the results of the polishing experiments are presented
Physics of the Power Corrections in QCD
We review the physics of the power corrections to the parton model. In the
first part, we consider the power corrections which characterize the infrared
sensitivity of Feynman graphs when the contribution of short distances
dominates. The second part is devoted to the hypothetical power corrections
associated with nonperturbative effects at small distances.Comment: 35 pages, 6 figures. Lecture given by V.I.Zakharov at the Winter
School of physics of ITEP, February 1999. Minor corrections, references adde
Confinement, Chiral Symmetry Breaking, and Axial Anomaly from Domain Formation at Intermediate Resolution
Based on general renormalization group arguments, Polyakov's loop-space
formalism, and recent analytical lattice arguments, suggesting, after Abelian
gauge fixing, a description of pure gluodynamics by means of a Georgi-Glashow
like model, the corresponding vacuum fields are defined in a non-local way.
Using lattice information on the gauge invariant field strength correlator in
full QCD, the resolution scale \La_b, at which these fields become relevant
in the vacuum, is determined. For SU(3) gauge theory it is found that
\La_b\sim 2.4 GeV, 3.1 GeV, and 4.2 GeV for ( MeV), ( MeV), and pure gluodynamics, repectively. Implications for the operator
product expansion of physical correlators are discussed. It is argued that the
emergence of magnetic (anti)monopoles in the vacuum at resolution \La_b is a
direct consequence of the randomness in the formation of a low entropy Higgs
condensate. This implies a breaking of chiral symmetry and a proliferation of
the axial U(1) anomaly at this scale already. Justifying Abelian projection, a
decoupling of non-Abelian gauge field fluctuations from the dynamics occurs.
The condensation of (anti)monopoles at \La_c<\La_b follows from the demand
that vacuum fields ought to have vanishing action at any resolution. As
monopoles condense they are reduced to their cores, and hence they become
massless. Apparently broken gauge symmetries at resolutions \La_c<\La\le\La_b
are restored in this process.Comment: 11 pages, 3 figure
Renormalizing a BRST-invariant composite operator of mass dimension 2 in Yang-Mills theory
We discuss the renormalization of a BRST and anti-BRST invariant composite
operator of mass dimension 2 in Yang-Mills theory with the general BRST and
anti-BRST invariant gauge fixing term of the Lorentz type. The interest of this
study stems from a recent claim that the non-vanishing vacuum condensate of the
composite operator in question can be an origin of mass gap and quark
confinement in any manifestly covariant gauge, as proposed by one of the
authors. First, we obtain the renormalization group flow of the Yang-Mills
theory. Next, we show the multiplicative renormalizability of the composite
operator and that the BRST and anti-BRST invariance of the bare composite
operator is preserved under the renormalization. Third, we perform the operator
product expansion of the gluon and ghost propagators and obtain the Wilson
coefficient corresponding to the vacuum condensate of mass dimension 2.
Finally, we discuss the connection of this work with the previous works and
argue the physical implications of the obtained results.Comment: 49 pages, 35 eps-files, A number of typographic errors are corrected.
A paragraph is added in the beginning of section 5.3. Two equations (7.1) and
(7.2) are added. A version to be published in Phys. Rev.
Blocking from continuum and monopoles in gluodynamics
We review the method of blocking of topological defects from continuum used
as a non--perturbative tool to construct effective actions for these defects.
The actions are formulated in the continuum limit while the couplings of these
actions can be derived from simple observables calculated numerically on
lattices with a finite lattice spacing. We demonstrate the success of the
method in deriving the effective actions for Abelian monopoles in the pure
SU(2) gauge models in an Abelian gauge. In particular, we discuss the
gluodynamics in three and four space--time dimensions at zero and non--zero
temperatures. Besides the action the quantities of our interest are the
monopole density, the magnetic Debye mass and the monopole condensate.Comment: 24 pages, 16 figures, RevTeX 4; To be published in Phys. Atom. Nucl.
dedicated to the 70th Birthday of Professor Yu. A. Simono
On ghost condensation, mass generation and Abelian dominance in the Maximal Abelian Gauge
Recent work claimed that the off-diagonal gluons (and ghosts) in pure
Yang-Mills theories, with Maximal Abelian gauge fixing (MAG), attain a
dynamical mass through an off-diagonal ghost condensate. This condensation
takes place due to a quartic ghost interaction, unavoidably present in MAG for
renormalizability purposes. The off-diagonal mass can be seen as evidence for
Abelian dominance. We discuss why ghost condensation of the type discussed in
those works cannot be the reason for the off-diagonal mass and Abelian
dominance, since it results in a tachyonic mass. We also point out what the
full mechanism behind the generation of a real mass might look like.Comment: 7 pages; uses revtex
First principles study of the origin and nature of ferromagnetism in (Ga,Mn)As
The properties of diluted GaMnAs are calculated for a wide range
of Mn concentrations within the local spin density approximation of density
functional theory. M\"ulliken population analyses and orbital-resolved
densities of states show that the configuration of Mn in GaAs is compatible
with either 3d or 3d, however the occupation is not integer due to the
large - hybridization between the Mn states and the valence band of
GaAs. The spin splitting of the conduction band of GaAs has a mean field-like
linear variation with the Mn concentration and indicates ferromagnetic coupling
with the Mn ions. In contrast the valence band is antiferromagnetically coupled
with the Mn impurities and the spin splitting is not linearly dependent on the
Mn concentration. This suggests that the mean field approximation breaks down
in the case of Mn-doped GaAs and corrections due to multiple scattering must be
considered. We calculate these corrections within a simple free electron model
and find good agreement with our {\it ab initio} results if a large exchange
constant (eV) is assumed.Comment: 15 pages, 14 figure
Thermodynamics of deformed AdS model with a positive/negative quadratic correction in graviton-dilaton system
By solving the Einstein equations of the graviton coupling with a real scalar
dilaton field, we establish a general framework to self-consistently solve the
geometric background with black-hole for any given phenomenological holographic
models. In this framwork, we solve the black-hole background, the corresponding
dilaon field and the dilaton potential for the deformed AdS model with a
positive/negative quadratic correction. We systematically investigate the
thermodynamical properties of the deformed AdS model with a positive and
negative quadratic correction, respectively, and compare with lattice QCD on
the results of the equation of state, the heavy quark potential, the Polyakov
loop and the spatial Wilson loop. We find that the bulk thermodynamical
properties are not sensitive to the sign of the quadratic correction, and the
results of both deformed holographic QCD models agree well with lattice QCD
result for pure SU(3) gauge theory. However, the results from loop operators
favor a positive quadratic correction, which agree well with lattice QCD
result. Especially, the result from the Polyakov loop excludes the model with a
negative quadratic correction in the warp factor of .Comment: 26 figures,36 pages,V.3: an appendix,more equations and references
added,figures corrected,published versio
Quark-antiquark potential with retardation and radiative contributions and the heavy quarkonium mass spectra
The charmonium and bottomonium mass spectra are calculated with the
systematic account of all relativistic corrections of order v^2/c^2 and the
one-loop radiative corrections. Special attention is paid to the contribution
of the retardation effects to the spin-independent part of the quark-antiquark
potential, and a general approach to accounting for retardation effects in the
long-range (confining) part of the potential is presented. A good fit to
available experimental data on the mass spectra is obtained.Comment: 20 pages, revtex, 2 Postscript figure
Molecular Plasmonic Silver Forests for the Photocatalytic-Driven Sensing Platforms
Structural electronics, as well as flexible and wearable devices are applications that are possible by merging polymers with metal nanoparticles. However, using conventional technologies, it is challenging to fabricate plasmonic structures that remain flexible. We developed three-dimensional (3D) plasmonic nanostructures/polymer sensors via single-step laser processing and further functionalization with 4-nitrobenzenethiol (4-NBT) as a molecular probe. These sensors allow ultrasensitive detection with surface-enhanced Raman spectroscopy (SERS). We tracked the 4-NBT plasmonic enhancement and changes in its vibrational spectrum under the chemical environment perturbations. As a model system, we investigated the sensor’s performance when exposed to prostate cancer cells’ media over 7 days showing the possibility of identifying the cell death reflected in the environment through the effects on the 4-NBT probe. Thus, the fabricated sensor could have an impact on the monitoring of the cancer treatment process. Moreover, the laser-driven nanoparticles/polymer intermixing resulted in a free-form electrically conductive composite that withstands over 1000 bending cycles without losing electrical properties. Our results bridge the gap between plasmonic sensing with SERS and flexible electronics in a scalable, energy-efficient, inexpensive, and environmentally friendly way.</p
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