Black Holes in Cascading Theories: Confinement/Deconfinement Transition and other Thermal Properties

We present numerical evidence for a transition between the Klebanov-Strassler background and a solution describing a black hole in the class of cascading solutions in the chirally restored phase. We also present a number of properties of this solution, including the running of the coupling constant, the viscosity to entropy ratio and the drag force on a quark moving in this background.Comment: 34 pages, 7 figures. Version to be published by JHE

Holographic Entanglement Entropy at Finite Temperature

Using a holographic proposal for the entanglement entropy we study its behavior in various supergravity backgrounds. We are particularly interested in the possibility of using the entanglement entropy as way to detect transitions induced by the presence horizons. We consider several geometries with horizons: the black hole in $AdS_3$, nonextremal Dp-branes, dyonic black holes asymptotically to $AdS_4$ and also Schwarzschild black holes in global $AdS_p$ coordinates. Generically, we find that the entanglement entropy does not exhibit a transition, that is, one of the two possible configurations always dominates.Comment: v3: 31 pp, ten figures, modified to match version accepted by IJMP

Global monopole, dark matter and scalar tensor theory

In this article, we discuss the space-time of a global monopole field as a candidate for galactic dark matter in the context of scalar tensor theory.Comment: 8 pages, Accepted in Mod. Phys. Lett.

On Penrose Limits and Gauge Theories

We discuss various Penrose limits of conformal and nonconformal backgrounds. In AdS_5 x T^{1,1}, for a particular choice of the angular coordinate in T^{1,1} the resulting Penrose limit coincides with the similar limit for AdS_5 x S^5. In this case an identification of a subset of field theory operators with the string zero modes creation operators is possible. For another limit we obtain a light-cone string action that resembles a particle in a magnetic field. We also consider three different types of backgrounds that are dual to nonconformal field theories: The Schwarzschild black hole in AdS_5, D3-branes on the small resolution of the conifold and the Klebanov-Tseytlin background. We find that in all three cases the introduction of nonconformality renders a theory that is no longer exactly solvable and that the form of the deformation is universal. The corresponding world sheet theory in the light-cone gauge has a \tau=x^+ dependent mass term.Comment: 17pp, late

Cambios florísticos inducidos por los incendios en repoblaciones de Pinus sylvestris en el noroeste de España

The effects of wildfire on vegetation regeneration in the understory of stands dominated by Pinus sylvestris L. in north-west Spain were analysed. In order to study changes in the composition of this community, three study areas dominated by Pinus sylvestris L. and burned by a summer wildfire were selected. In each area three permanent plots of 25 × 1 m2 was established. The cover percentage of plant species present, and the cover of life forms and richness were analysed yearly from the first to the fourth year after fire. Total cover values generally increased throughout the study period. The species that appeared during the first years were those that would dominate in the mature stage, such as Erica australis L. and Pterospartum tridentatum (L.) Willk, both species being typical resprouters. Other species that appeared from the first year are typical seeders like Pinus sylvestris L. and Halimium alyssoides (Lam.) K. Koch. Floristic richness values showed higher values during the first year after fire than in the original situation, due to the fast recovery of the herbaceous species in the open spaces created by fire. After the first year changes in richness values were not significantLos efectos del fuego sobre la regeneración de las comunidades vegetales en plantaciones de Pinus sylvestris L. en el noroeste de España han sido analizados. Para analizar los cambios en la composición y estructura de este tipo de comunidades, se seleccionaron tres zonas de estudio en plantaciones de Pinus sylvestris L. y en ellas se seleccionaron áreas quemadas por un incendio de verano. En cada una de estas áreas se instalaron tres parcelas permanentes de 25 × 1 m2 donde se midió el porcentaje de cobertura por especies cada año desde un año hasta cuatro después del incendio. Los valores de cobertura total se incrementaron de forma gradual durante el periodo estudiado. Las especies que aparecen durante los primeros años son las que dominan en las etapas maduras, como Erica australis L. Pterospartum tridentatum (L.) Wilk. Otras especies que aparecen desde el primer año se regeneran obligatoriamente de semillas como Pinus sylvestris L. y Halimium alyssoides (Lam.) K. Koch. Los valores de riqueza florística encontrados en el primer año tras el incendio son mayores que los de la situación original debido a la rápida recuperación de las herbáceas en los espacios abiertos creados por el fuego. A partir del primer año los cambios en riqueza no fueron significativo

Penrose Limits and RG Flows

The Penrose-Gueven limit simplifies a given supergravity solution into a pp-wave background. Aiming at clarifying its relation to renormalization group flow we study the Penrose-Guven limit of supergravity backgrounds that are dual to non-conformal gauge theories. The resulting backgrounds fall in a class simple enough that the quantum particle is exactly solvable. We propose a map between the effective time-dependent quantum mechanical problem and the RG flow in the gauge theory. As a testing ground we consider explicitly two Penrose limits of the infrared fixed point of the Pilch-Warner solution. We analyze the corresponding gauge theory picture and write down the operators which are the duals of the low lying string states. We also address RG flows of a different nature by considering the Penrose-Gueven limit of a stack of N D_p branes. We note that in the far IR (for p<3)the limit generically has negative mass-squared. This phenomenon signals, in the world sheet picture, the necessity to transform to another description. In this regard, we consider explicitly the cases of M2 from D2 and F1 from D1 .Comment: 35 pp, 6 figure

The Combined Strength of Thermodynamics and Comparative Planetology: Application of Activity Models to Core Formation in Terrestrial Bodies

Recent models for accretion of terrestrial bodies involve metal-silicate equilibrium as the metallic core formed during growth. Most elements considered are either refractory or well studied elements for which effects of pressure, temperature, oxygen fugacity, and metallic liquid composition are well known. There are a large number of elements that are both siderophile and volatile, whose fate in such models is unknown, largely due to a lack of data at comparable conditions and com-positions (FeNi core with light elements such as S, C, Si, and O). We have focused on Ge, In, As, Sb and determined the effect of Si and C on metal-silicate partitioning, and developed a thermo-dynamic model that allows application of these new data to a wide range of planetary bodies. New experiments: We have previously carried out experiments with FeSi metallic liquid at C-saturated conditions at 1600 and 1800 C [4]. In a new series of experiments we investigate the effect of Si in carbon-free systems at 1600 C for comparison. Experiments were carried out at 1 GPa in MgO capsules using the same basaltic starting composition as in previous studies. The MgO capsule reacts with the silicate melt to form more MgO-rich liquids that have 22-26 wt% MgO. Experimental met-als and silicates were analyzed using a combination of electron microprobe analysis and laser ablation ICP-MS. Results: The new results can be interpreted by considering Ge as an example, in the simple exchange equilibrium Fe + GeO = FeO + Ge, where the equilibrium constant Kd can be examined as a function of Si content of the metal. The slope of lnKd vs. (1-XSi) for this new series allows derivation of the epsilon interaction parameter for each of these four elements and Si (both C-saturated and C-free).All four elements have positive epsilon values, indicating that Si causes a decrease in the partition coefficients; values are 6.6, 6.5, 27.8 and 25.2 for In, Ge, As, and Sb, respectively, at 1 GPa and 1600 C. As an example of how large the effect of Si can be, these epsilon values correspond to activity coefficients (gamma) for As of 0.01 when XSi = 0, and up to gamma = 23 when XSi = 0.2. Combining these new results with previous determinations [5,6] of epsilon parameters for S and C for these elements allows us calculate activity of Ge, In, As, and Sb in Fe-Ni-Si-S-C-O metallic liquids. We apply this new model to sever-al terrestrial bodies such as Earth (Si-rich core), Mars (S-rich core), Moon (S-, C-, and Si-poor core), and Vesta, and examine the resulting core and mantle concentrations of these elements. Mantle concentrations of these four elements are well explained for Earth and Mars in models that call for mid-mantle equilibration between Si-bearing and S-bearing FeNi cores, respectively. Modeling results for the Moon and Vesta will also be presented

Liquefaction Potential of Railway Embankments

This paper presents an overview of the nature of train-induced vibrations and discusses the liquefaction potential of railway embankments under such low-level vibrations. The paper also presents the results of static and dynamic finite difference numerical analyses performed for a simple railway embankment geometry. The liquefaction potential for the railway embankment foundation was estimated using the results corn FLAC numerical analyses, as well as a cyclic shear stress liquefaction resistance approach using a modified cyclic resistance ratio curve. Liquefaction of railway embankment foundations was found to be possible. However, based on the majority of reported failures the liquefaction potential remains low unless the train-induced vibrations are coupled with factors such as loose foundation, and sudden rise of pore water pressures due to poor drainage, flooding, or heavy rainfall

On a Holographic Model for Confinement/Deconfinement

We study the thermodynamics of the hard wall model, which consists in the introduction of an infrared cut-off in asymptotically AdS spaces. This is a toy model for confining backgrounds in the context of the gauge/gravity correspondence. We use holographic renormalization and reproduce the existence of a Hawking Page phase transition recently discussed by Herzog. We also show that the entropy jumps from $N^0$ to $N^2$, which reinforces the interpretation of this transition as the gravity dual of confinement/deconfinement. We also show that similar results hold for the phenomenologically motivated soft wall model, underlining the potential universality of our analysis.Comment: 14 pages. V2: We included a new section discussing the soft wall model and new references. V3: We clarified some points and updated the references. Results unchanged. Version published in PR

Photographing the wave function of the Universe

We show that density fluctuations in standard inflationary scenarios may take the most general non-Gaussian distribution if the wave function of the Universe is not in the ground state. We adopt the Schr\"odinger picture to find a remarkable similarity between the most general inflaton wavefunction and the Edgeworth expansion used in probability theory. Hence we arrive at an explicit relation between the cumulants of the density fluctuations and the amplitudes or occupation numbers of the various energy eigenstates. For incoherent superpositions only even cumulants may be non-zero, but coherent superpositions may generate non-zero odd cumulants as well. Within this framework measurements of cumulants in Galaxy surveys directly map the wavefunction of the Universe.Comment: Replaced with revised version Latex, 10 pages., accepted for publication in Phys. Lett.