Characteristic length of an AdS/CFT superconductor

We investigate in more detail the holographic model of a superconductor recently found by Hartnoll, Herzog, and Horowitz [Phys. Rev. Lett. 101, 031601], which is constructed from a condensate of a charged scalar field in AdS_4-Schwarzschild background. By analytically studying the perturbation of the gravitational system near the critical temperature T_c, we obtain the superconducting coherence length proportional to 1/\sqrt{1-T/T_c} via AdS/CFT correspondence. By adding a small external homogeneous magnetic field to the system, we find that a stationary diamagnetic current proportional to the square of the order parameter is induced by the magnetic field. These results agree with Ginzburg-Landau theory and strongly support the idea that a superconductor can be described by a charged scalar field on a black hole via AdS/CFT duality.Comment: 9 pages, no figure; v2: typos corrected; v3: version to appear in PRD, an early discussion based on convensional superconductor with dynamical photon removed and an argument about the type of the holographic superconductor adde

Static and symmetric wormholes respecting energy conditions in Einstein-Gauss-Bonnet gravity

Properties of $n(\ge 5)$-dimensional static wormhole solutions are investigated in Einstein-Gauss-Bonnet gravity with or without a cosmological constant $\Lambda$. We assume that the spacetime has symmetries corresponding to the isometries of an $(n-2)$-dimensional maximally symmetric space with the sectional curvature $k=\pm 1, 0$. It is also assumed that the metric is at least $C^{2}$ and the $(n-2)$-dimensional maximally symmetric subspace is compact. Depending on the existence or absence of the general relativistic limit $\alpha \to 0$, solutions are classified into general relativistic (GR) and non-GR branches, respectively, where $\alpha$ is the Gauss-Bonnet coupling constant. We show that a wormhole throat respecting the dominant energy condition coincides with a branch surface in the GR branch, otherwise the null energy condition is violated there. In the non-GR branch, it is shown that there is no wormhole solution for $k\alpha \ge 0$. For the matter field with zero tangential pressure, it is also shown in the non-GR branch with $k\alpha<0$ and $\Lambda \le 0$ that the dominant energy condition holds at the wormhole throat if the radius of the throat satisfies some inequality. In the vacuum case, a fine-tuning of the coupling constants is shown to be necessary and the radius of a wormhole throat is fixed. Explicit wormhole solutions respecting the energy conditions in the whole spacetime are obtained in the vacuum and dust cases with $k=-1$ and $\alpha>0$.Comment: 10 pages, 2 tables; v2, typos corrected, references added; v3, interpretation of the solution for n=5 in section IV corrected; v4, a very final version to appear in Physical Review

New Charged Black Holes with Conformal Scalar Hair

A new class of four-dimensional, hairy, stationary solutions of the Einstein-Maxwell-Lambda system with a conformally coupled scalar field is constructed in this paper. The metric belongs to the Plebanski-Demianski family and hence its static limit has the form of the charged C-metric. It is shown that, in the static case, a new family of hairy black holes arises. They turn out to be cohomogeneity-two, with horizons that are neither Einstein nor homogenous manifolds. The conical singularities in the C-metric can be removed due to the back reaction of the scalar field providing a new kind of regular, radiative spacetime. The scalar field carries a continuous parameter proportional to the usual acceleration present in the C-metric. In the zero-acceleration limit, the static solution reduces to the dyonic Bocharova-Bronnikov-Melnikov-Bekenstein solution or the dyonic extension of the Martinez-Troncoso-Zanelli black holes, depending on the value of the cosmological constant.Comment: Published versio

Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature

We present a high-resolution microwave spectrometer to measure the frequency-dependent complex conductivity of a superconducting thin film near the critical temperature. The instrument is based on a broadband measurement of the complex reflection coefficient, $S_{\rm 11}$, of a coaxial transmission line, which is terminated to a thin film sample with the electrodes in a Corbino disk shape. In the vicinity of the critical temperature, the standard calibration technique using three known standards fails to extract the strong frequency dependence of the complex conductivity induced by the superconducting fluctuations. This is because a small unexpected difference between the phase parts of $S_{\rm 11}$ for a short and load standards gives rise to a large error in the detailed frequency dependence of the complex conductivity near the superconducting transition. We demonstrate that a new calibration procedure using the normal-state conductivity of a sample as a load standard resolves this difficulty. The high quality performance of this spectrometer, which covers the frequency range between 0.1 GHz and 10 GHz, the temperature range down to 10 K, and the magnetic field range up to 1 T, is illustrated by the experimental results on several thin films of both conventional and high temperature superconductors.Comment: 13 pages, 14 figure

Subaru and Keck Observations of the Peculiar Type Ia Supernova 2006gz at Late Phases

Recently, a few peculiar Type Ia supernovae (SNe) that show exceptionally large peak luminosity have been discovered. Their luminosity requires more than 1 Msun of 56Ni ejected during the explosion, suggesting that they might have originated from super-Chandrasekhar mass white dwarfs. However, the nature of these objects is not yet well understood. In particular, no data have been taken at late phases, about one year after the explosion. We report on Subaru and Keck optical spectroscopic and photometric observations of the SN Ia 2006gz, which had been classified as being one of these "overluminous" SNe Ia. The late-time behavior is distinctly different from that of normal SNe Ia, reinforcing the argument that SN 2006gz belongs to a different subclass than normal SNe Ia. However, the peculiar features found at late times are not readily connected to a large amount of 56Ni; the SN is faint, and it lacks [Fe II] and [Fe III] emission. If the bulk of the radioactive energy escapes the SN ejecta as visual light, as is the case in normal SNe Ia, the mass of 56Ni does not exceed ~ 0.3 Msun. We discuss several possibilities to remedy the problem. With the limited observations, however, we are unable to conclusively identify which process is responsible. An interesting possibility is that the bulk of the emission might be shifted to longer wavelengths, unlike the case in other SNe Ia, which might be related to dense C-rich regions as indicated by the early-phase data. Alternatively, it might be the case that SN 2006gz, though peculiar, was actually not substantially overluminous at early times.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in The Astrophysical Journa

Dynamic Evolution of Flux Distributions in a Pulse-driven Superconductor by High-speed Magneto-optical Imaging

The accurate understanding of flux dynamics is essential for the design and operation of superconducting circuits. The time evolution of flux-density distribution in an NbN strip by the transport current was observed using high-speed magneto-optical microscopy. It was determined that even for the dynamic penetration and exclusion of vortices under the transport current, the surface barrier is essential. This feature is important for the correct understanding of the complex behavior of state-of-the-art superconducting devices

AN ECONOMIC EVALUATION OF THE NEW AGRICULTURAL TRADE NEGOTIATIONS: A NONLINEAR IMPERFECTLY COMPETITIVE SPATIAL EQUILIBRIUM APPROACH

The objective of the research reported here is to develop a more flexible and comprehensive policy simulation model for imperfectly competitive international agricultural trade with various trade and domestic support policies. The model is a nonlinear imperfectly competitive spatial equilibrium model formulated as a MCP. The model is flexible in that it can simulate the economic effects of the following trade policies: specific duties, ad valorem tariffs, tariff-rate quotas, export subsidies, production subsidies, production quotas, consumption taxes and price floor, combined with various imperfectly competitive market structures. The usefulness of the model is demonstrated with an application to international wheat trade simulated under several alternative scenarios based on proposals of major countries as well as the agreement between China and the United States on China's participation in the 11'70. The main empirical findings are as follows. Keeping the committed 1000 support levels under the current WTO agricultural agreements would be favorable for wheat producers in tile European Community and Canada, but harmful to the United States w-heat sector. There would be little structural change in the world wheat trade in a case where China joins the WTO, keeping the other countries' policies at the committed 2000 support levels. Likewise, little structural change would occur in the case where the new WTO agricultural negotiations result in agreements favorable for importing countries. However, world wheat trade would drastically change under full trade liberalization. In this case, the European Community switches from the world's leading net exporter to the world's leading net importer of wheat. Also, China and India would become major net exporting countries, and net exports by the United States, Canada, and the Cairns group such as Australia and Argentina would expand tinder full trade liberalization.International Relations/Trade,

Origin of matter out of pure curvature

We propose a mechanism for origin of matter in the universe in the framework of Einstein-Gauss-Bonnet gravity in higher dimensions. The recently discovered new static black hole solution by the authors \cite{md2006} with the Kaluza-Klein split up of spacetime as a product of the usual {\ma M}^4 with a space of negative constant curvature is indeed a pure gravitational creation of a black hole which is also endowed with a Maxwell-like {\it gravitational charge} in four-dimensional vacuum spacetime. Further it could be envisioned as being formed from anti-de Sitter spacetime by collapse of radially inflowing charged null dust. It thus establishes the remarkable reciprocity between matter and gravity - as matter produces gravity (curvature), gravity too produces matter.Comment: 8 pages, 1 Fig, Received Honorable Mention in 2007 GRF Essay Competition, Summary of the talk given at Himalayan Relativity Dialogue at Mirik, April 18-20, 200

EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC

The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis