5,032 research outputs found
Zero Temperature Limit of Holographic Superconductors
We consider holographic superconductors whose bulk description consists of
gravity minimally coupled to a Maxwell field and charged scalar field with
general potential. We give an analytic argument that there is no "hard gap":
the real part of the conductivity at low frequency remains nonzero (although
typically exponentially small) even at zero temperature. We also numerically
construct the gravitational dual of the ground state of some holographic
superconductors. Depending on the charge and dimension of the condensate, the
infrared theory can have emergent conformal or just Poincare symmetry. In all
cases studied, the area of the horizon of the dual black hole goes to zero in
the extremal limit, consistent with a nondegenerate ground state.Comment: 27 pages, 8 figure
Power corrections to the transition form factor and pion distribution amplitudes
Employing the standard hard-scattering approach and the running coupling
method we calculate a class of power-suppressed corrections to the electromagnetic transition form
factor (FF) arising from the end-point
integration regions. In the investigations we use a hard-scattering amplitude
of the subprocess , symmetrized under
exchange important for exclusive
processes containing two external photons. In the computations the pion model
distribution amplitudes (DA's) with one and two non-asymptotic terms are
employed. The obtained predictions are compared with the CLEO data and
constraints on the DA parameters and at the
normalization point are extracted. Further restrictions on
the pion DA's are deduced from the experimental data on the electromagnetic FF
.Comment: 23 pages, 6 figures; the version published in Phys. Rev. D69, 094010
(2004
Additive N-Step Markov Chains as Prototype Model of Symbolic Stochastic Dynamical Systems with Long-Range Correlations
A theory of symbolic dynamic systems with long-range correlations based on
the consideration of the binary N-step Markov chains developed earlier in Phys.
Rev. Lett. 90, 110601 (2003) is generalized to the biased case (non equal
numbers of zeros and unities in the chain). In the model, the conditional
probability that the i-th symbol in the chain equals zero (or unity) is a
linear function of the number of unities (zeros) among the preceding N symbols.
The correlation and distribution functions as well as the variance of number of
symbols in the words of arbitrary length L are obtained analytically and
verified by numerical simulations. A self-similarity of the studied stochastic
process is revealed and the similarity group transformation of the chain
parameters is presented. The diffusion Fokker-Planck equation governing the
distribution function of the L-words is explored. If the persistent
correlations are not extremely strong, the distribution function is shown to be
the Gaussian with the variance being nonlinearly dependent on L. An equation
connecting the memory and correlation function of the additive Markov chain is
presented. This equation allows reconstructing a memory function using a
correlation function of the system. Effectiveness and robustness of the
proposed method is demonstrated by simple model examples. Memory functions of
concrete coarse-grained literary texts are found and their universal power-law
behavior at long distances is revealed.Comment: 19 pages, 8 figure
Research Progress of Coloring Aluminum Pigments by Corrosion Protection Method
AbstractWith the increasing of the aesthetic value of people and pursue of colorful, coloring aluminum pigments will have broad application prospects. Chromatic sliver printing ink is a kind of flake aluminum pigments which has had the surface modification treatment. It has metallic luster of aluminum powder and chromatic colors at the same time. Chromatic aluminum pigments is widely used in automobile, coatings, printing ink, printing and dyeing, etc industries and fields such as art adornment because of its characteristics such as chromatic color, strong corrosion resistance, good insulation, permanent, strong mental luster, low cost and so on. So preparing a new kind of chromatic silver plasma ink is of great significance. The reporting of domestic and international documents of coloring aluminum pigments by corrosion protection methods mainly are adsorptive, sedimentation and coating method
Cosmic tomography with weak gravitational lensing
We explored the Universe using weak gravitational lensing, a phenomenon that occurs when light from distant galaxies is bent by the gravitational fields of closer cosmic objects, much like how a lens distorts light. Studying these distortions gives us insights into massive objects, such as galaxy clusters, and the large-scale structure of the Universe. However, analysing these weak lensing effects, though powerful, is challenging. Accurately detecting and interpreting these minute distortions require careful management of uncertainties, both from observational techniques and the models we employ. In our study, we rigorously controlled these uncertainties. By enhancing our analysis methods, we provided more accurate constraints on key cosmological parameters. Furthermore, we studied lensing effects around galaxy groups, shedding light on the relationship between the enigmatic dark matter – a difficult-to-detect but predominant component of the Universe – and the galaxies we observe. In conclusion, our research advanced the weak lensing analysis and broadened our understanding of the Universe.Galaxie
Aspects of the Screening Length and Drag Force in Two Alternative Gravity Duals of the Quark-gluon Plasma
We compute the screening length of mesons with different angular momentum
from two gravity dual theories. Both the asymptotically and
Sakai-Sugimoto metrics are considered in the calculations. Using the dual
description of the quark as a classical string ending on the probe brane, we
obtain the interacting potential between the heavy quark and antiquark after
rotating the background metric. The result shows that the screening length of
mesons with different is well fit to . The constant is
determined for by taking advantage of numerical techniques. Finally,
we calculate the drag force and relaxation times from the Sakai-Sugimoto metric
and compare with the ones obtained in the . The application of our
result to charmonium and bottomonium at RHIC and LHC is briefly discussed.Comment: 18 pages, 6 figures, 2 tables, version to appear in JHEP,
acknowledgment adde
Appearance and disappearance of superconductivity in SmFe1-xNixAsO (x = 0.0 to 1.0)
Bulk polycrystalline Ni-substituted SmFe1-xNixAsO (x = 0.0 to 1.0) samples
are synthesized by solid state reaction route in an evacuated sealed quartz
tube. The cell volume decreases with increase of Ni content in SmFe1-xNixAsO,
thus indicating successful substitution of smaller ion Ni at Fe site. The
resistivity measurements showed that the spin-density-wave (SDW) transition is
suppressed drastically with Ni doping and subsequently superconductivity is
achieved in a narrow range of x from 0.04 to 0.10 with maximum Tc of 9K at x =
0.06. For higher content of Ni (x > 0.10), the system becomes metallic and
superconductivity is not observed down to 2K. The magneto-transport [R(T)H]
measurements exhibited the upper critical field [Hc2(0)] of up to 300kOe. The
flux flow activation energy (U/kB) is estimated ~98.37K for 0.1T field.
Magnetic susceptibility measurements also confirms bulk superconductivity for x
= 0.04, 0.06 and 0.08 samples. The lower critical field (Hc1) is around 100Oe
at 2K for x = 0.06 sample. Heat capacity CP(T) measurements exhibited a hump
like transition pertaining to SDW in Fe planes at around 150K and an AFM
ordering of Sm spins below temperature of 5.4K for ordered Sm spins [TN(Sm)].
Though, the SDW hump for Fe spins disappears for Ni doped samples, the TN (Sm)
remains unaltered but with a reduced transition height, i.e., decreased
entropy. In conclusion, complete phase diagram of SmFe1-xNixAsO (x = 0.0 to
1.0) is studied in terms of its structural, electrical, magnetic and thermal
properties.Comment: 18 pages text + Figures; comments suggestions welcome
([email protected]
Radiative Tau Lepton Pair Production as a Probe of Anomalous Electromagnetic Couplings of the Tau
We calculate the squared matrix element for the process e+ e- --> tau+ tau-
gamma allowing for anomalous magnetic and electric dipole moments at the tau
tau gamma vertex. No interferences are neglected and no approximations of light
fermion masses are made. We show that anomalous moments affect not only the
cross section, but also the shape of the photon energy and angular
distributions. We also demonstrate that in the case of the anomalous magnetic
dipole moment, the contribution from interference involving Standard Model and
anomalous amplitudes is significant compared to the contribution from anomalous
amplitudes alone. A program to perform the calculation is available and it may
be employed as a Monte Carlo generator.Comment: 14 pages, 8 figures submitted to Nuclear Physics
Improved superconducting properties of MgB2
We present electrical transport, magnetization, and specific heat
measurements on bulk MgB2 samples (T_{c} = 38.5 K) synthesized under 200 MPa
pressure using a process based on hot isostatic pressing with cooling under
pressure. The samples are fully dense and display excellent superconducting
properties, including a narrow superconducting transition width (\Delta T_{c} =
0.75 K), a high upper critical field H_{c2} (H_{c2}(0) ~ 155 kOe), and a
critical current density J_{c} that is the largest yet measured for bulk
samples of MgB2 (J_{c}(0) ~ 1.4 MA/cm^{2}). Specific heat measurements yielded
a jump \Delta C at T_{c} of 92 mJ/mol K. These superconducting properties are
comparable to those obtained with techniques that are not so well suited to
industrial scale fabrication.Comment: 7 text pages, 5 figures, submitted to Physica
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