Consequences of the partial restoration of chiral symmetry in AdS/QCD

Chiral symmetry is an essential concept in understanding QCD at low energy. We treat the chiral condensate, which measures the spontaneous breaking of chiral symmetry, as a free parameter to investigate the effect of partially restored chiral symmetry on the physical quantities in the frame work of an AdS/QCD model. We observe an interesting scaling behavior among the nucleon mass, pion decay constant and chiral condensate. We propose a phenomenological way to introduce the temperature dependence of a physical quantity in the AdS/QCD model with the thermal AdS metric.Comment: 11 pages, 6 figure

Heavy quarkonium in a holographic QCD model

Encouraged by recent developments in AdS/QCD models for light quark system, we study heavy quarkonium in the framework of the AdS/QCD models. We calculate the masses of $c\bar c$ vector meson states using the AdS/QCD models at zero and at finite temperature. Among the models adopted in this work, we find that the soft wall model describes the low-lying heavy quark meson states at zero temperature relatively well. At finite temperature, we observe that once the bound state is above $T_c$, its mass will increase with temperature until it dissociates at a temperature of around $494 {\rm MeV}$. It is shown that the dissociation temperature is fixed by the infrared cutoff of the models. The present model serves as a unified non perturbative model to investigate the properties of bound quarkonium states above $T_c$.Comment: 9 pages, 1 figure, minor revision, to appear in phys. Rev.

A criterion for the nature of the superconducting transition in strongly interacting field theories : Holographic approach

It is beyond the present techniques based on perturbation theory to reveal the nature of phase transitions in strongly interacting field theories. Recently, the holographic approach has provided us with an effective dual description, mapping strongly coupled conformal field theories to classical gravity theories. Resorting to the holographic superconductor model, we propose a general criterion for the nature of the superconducting phase transition based on effective interactions between vortices. We find "tricritical" points in terms of the chemical potential for U(1) charges and an effective Ginzburg-Landau parameter, where vortices do not interact to separate the second order (repulsive) from the first order (attractive) transitions. We interpret the first order transition as the Coleman-Weinberg mechanism, arguing that it is relevant to superconducting instabilities around quantum criticality.Comment: 7 pages, 7 figure

Network Structures and the Properties of Na-Ca-Sr-Borophosphate Glasses

Borophosphate glasses were prepared with the nominal molar compositions 16Na2O-(24-y)CaO-ySrO-xB2O3-(60-x)P2O5 (mol%), where 0≤x≤60 and y=0, 12, and 24. Information about the compositional dependence of borate and phosphate site speciation and next nearest neighbor linkages was obtained by 11B and 31P MAS NMR and Raman spectroscopies, and by high pressure liquid chromatography (HPLC). With the initial replacement of P2O5 by B2O3, tetrahedral borate sites linked to four phosphate anions, B(ØP)4, are created in the glass structure, and the average phosphate anion becomes smaller as bridging PØP bonds are replaced by bridging PØB bonds. With further increases in the B2O3 content, borate units, including B-triangles, replace phosphate units linked to the B-tetrahedra. Compositional trends for the glass transition temperature (Tg) and molar volume are explained by considering the number and types of bridging oxygens per glass former, consistent with topological models reported elsewhere

Mesons and nucleons from holographic QCD in a unified approach

We investigate masses and coupling constants of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. We first examine an appropriate form of fermionic solutions by restricting the mass coupling for the five dimensional bulk fermions and bosons. We then derive approximated analytic solutions for the nucleons and the corresponding masses in a small mass coupling region. In order to treat meson and nucleon properties on the same footing, we introduce the same infrared (IR) cut in such a way that the meson-nucleon coupling constants, i.e., g_{pi NN} and g_{rho NN} are uniquely determined. The first order approximation with respect to a dimensionless expansion parameter, which is valid in the small mass coupling region, explicitly shows difficulties to avoid the IR scale problem of the hard wall model. We discuss possible ways of circumventing these problems.Comment: 15 pages, No figure. Several typos have been remove

The XWS open access catalogue of extreme European windstorms from 1979 to 2012

The XWS (eXtreme WindStorms) catalogue consists of storm tracks and model-generated maximum 3 s wind-gust footprints for 50 of the most extreme winter windstorms to hit Europe in the period 1979–2012. The catalogue is intended to be a valuable resource for both academia and industries such as (re)insurance, for example allowing users to characterise extreme European storms, and validate climate and catastrophe models. Several storm severity indices were investigated to find which could best represent a list of known high-loss (severe) storms. The best-performing index was Sft, which is a combination of storm area calculated from the storm footprint and maximum 925 hPa wind speed from the storm track. All the listed severe storms are included in the catalogue, and the remaining ones were selected using Sft. A comparison of the model footprint to station observations revealed that storms were generally well represented, although for some storms the highest gusts were underestimated. Possible reasons for this underestimation include the model failing to simulate strong enough pressure gradients and not representing convective gusts. A new recalibration method was developed to estimate the true distribution of gusts at each grid point and correct for this underestimation. The recalibration model allows for storm-to-storm variation which is essential given that different storms have different degrees of model bias. The catalogue is available at www.europeanwindstorms.org

Symmetry energy of dense matter in holographic QCD

We study the nuclear symmetry energy of dense matter using holographic QCD. To this end, we consider two flavor branes with equal quark masses in a D4/D6/D6 model. We find that at all densities the symmetry energy monotonically increases. At small densities, it exhibits a power law behavior with the density, $E_{\rm sym} \sim \rho^{1/2}$.Comment: 9 pages, 3 figure

Hybrid exotic meson with J^{PC}=1^{-+} in AdS/QCD

We investigate the hybrid exotic meson with $J^{PC}=1^{-+}$ within the framework of an AdS/QCD model. Introducing a holographic field dual to the operator for hybrid exotic meson, we obtain the eigen-value equation for its mass. Fixing all free parameters by QCD observables such as the $\rho$-meson mass, we predict the masses of the hybrid exotic meson. The results turn out to be $1476 \mathrm{MeV}$ for the ground state, and $2611 \mathrm{MeV}$ for the first excited one. Being compared with the existing experimental data for the $\pi_1(1400)$, which is known to be $m_{\pi_1} = 1351\pm30 \mathrm{MeV}$, the present result seems to be qualitative in agreement with it. We also predict the decay constant of $\pi_1$(1400): $F_{\pi_1}= 10.6$ MeV.Comment: 10 pages, 1 Tabl