On AdS to dS transitions in higher-curvature gravity

We study the possible existence of gravitational phase transitions from AdS to dS geometries in the context of higher-curvature gravities. We use Lanczos-Gauss-Bonnet (LGB) theory with a positive cosmological constant as a toy model. This theory has two maximally symmetric vacua with positive (dS) and negative (AdS) constant curvature. We show that a phase transition from the AdS vacuum to a dS black hole geometry takes place when the temperature reaches a critical value. The transition is produced by nucleation of bubbles of the new phase that expand afterwards. We claim that this phenomenon is not particular to the model under study, and shall also be part of generic gravitational theories with higher-curvature terms.Comment: 12 pages, 3 figures; v2: comments and references adde

Holographic Ward identities for symmetry breaking in two dimensions

We investigate symmetry breaking in two-dimensional field theories which have a holographic gravity dual. Being at large N, the Coleman theorem does not hold and Goldstone bosons are expected. We consider the minimal setup to describe a conserved current and a charged operator, and we perform holographic renormalization in order to find the correct Ward identities describing symmetry breaking. This involves some subtleties related to the different boundary conditions that a vector can have in the three-dimensional bulk. We establish which is the correct prescription that yields, after renormalization, the same Ward identities as in higher dimensions.Comment: 20 pages. v2 comments added. Version to appear in JHE

An analytical model of radial dust trapping in protoplanetary disks

We study dust concentration in axisymmetric gas rings in protoplanetary disks. Given the gas surface density, we derived an analytical total dust surface density by taking into account the differential concentration of all the grain sizes. This model allows us to predict the local dust-to-gas mass ratio and the slope of the particle size distribution, as a function of radius. We test this analytical model comparing it with a 3D magneto-hydrodynamical simulation of dust evolution in an accretion disk. The model is also applied to the disk around HD 169142. By fitting the disk continuum observations simultaneously at $\lambda = 0.87$, 1.3, 3.0 mm, we obtain a global dust-to-gas mass ratio $\epsilon_{\rm global} = 1.05 \times 10^{-2}$ and a viscosity coefficient $\alpha = 1.35 \times 10^{-2}$. This model can be easily implemented in numerical simulations of accretion disks

Porous Dust Particles in Protoplanetary Disks: Application to the HL Tau Disk

Dust particle sizes constrained from dust continuum and polarization observations by radio interferometry are inconsistent by at least an order of magnitude. Motivated by porous dust observed in small Solar System bodies (e.g., from the Rosetta mission), we explore how the dust particle's porosity affects the estimated particle sizes from these two methods. Porous particles have lower refractive indices, which affect both opacity and polarization fraction. With weaker Mie interference patterns, the porous particles have lower opacity at mm wavelengths than the compact particles if the particle size exceeds several hundred microns. Consequently, the inferred dust mass using porous particles can be up to a factor of six higher. The most significant difference between compact and porous particles is their scattering properties. The porous particles have a wider range of particle sizes with high linear polarization from dust self-scattering, allowing mm-cm-sized particles to explain polarization observations. With a Bayesian approach, we use porous particles to fit HL Tau disk's multi-wavelength continuum and mm-polarization observations from ALMA and VLA. The moderately porous particles with sizes from 1 mm-1 m can explain both continuum and polarization observations, especially in the region between 20-60 au. If the particles in HL Tau are porous, the porosity should be from 70% to 97% from current polarization observations. We also predict that future observations of the self-scattering linear polarization at longer wavelengths (e.g., ALMA B1 and ngVLA) have the potential to further constrain the particle's porosity and size.Comment: 39 pages, 18 figures, 1 table, accepted to be published in The Astrophysical Journa

Comportamiento de la variedad Nu OPAL (Gossypium hirsutum L.) bajo diferentes arreglos espaciales

This research was carried out to determine the spatial arrangement with higher yield potential field of Nu Opal cotton variety under the agroecological conditions of the middle Sinu Valley. Were evaluated six different population densities from the variation of the distances among rows (from 1,0; 0,9; 0,8; 0,7; 0,6 to 0,5 m) and setting two plants per meter. These were compared with the density of population used by farmers in the producing area (62.500 plants ha-1). Treatments were arranged in a design of a randomized complete block (RCBD) with four replications. Planting was carried out in the experimental station Turipaná CORPOICA CI in the second half of 2006. The results showed that the spatial arrangements used did not affect neither the expression of plant height and flowering, nor the components of fiber quality. In contrast, significant differences (P<0,05) for the number of buttons and field performance were encountered. The highest yield of cotton-seed and fiber was shown for the control treatment to 5370,7 and 2028,3 kg ha-1 respectively. Notably, the treatment of 40,000 plants ha-1 had similar yields to the control with 5137,4 kg ha-1 of cotton-seed and 1986,7 kg ha-1 of fiber, having numerical but not statistical difference (P>< 0,05) for the number of buttons and field performance were encountered. The highest yield of cotton-seed and fiber was shown for the control treatment to 5370,7 and 2028,3 kg ha-1 respectively. Notably, the treatment of 40,000 plants ha-1 had similar yields to the control with 5137,4 kg ha-1 of cotton-seed and 1986,7 kg ha-1 of fiber, having numerical but not statistical difference (P>0,05) between them.Esta investigación se realizó con el objetivo de determinar el arreglo espacial con mayor potencial de rendimiento de campo de la variedad de algodón Nu Opal bajo las condiciones agroecológicas del Valle del Sinú Medio. Se evaluaron seis densidades de población a partir de la variación de las distancias entre surcos (desde 1,0; 0,9; 0,8; 0,7; 0,6 y 0,5 m) y fijando dos plantas por metro. Estas fueron comparadas con la densidad de población utilizada por los agricultores (62.500 plantas ha-1). Los tratamientos fueron dispuestos en un diseño de bloques completos al azar (DBCA) con cuatro repeticiones. La siembra experimental se realizó en el centro experimental CORPOICA CI Turipaná en el segundo semestre del año 2006. Los resultados resaltan que los arreglos espaciales utilizados no afectaron  la altura de planta, floración ni los componentes de calidad de la fibra. En cambio, se encontraron diferencias significativas (P<0,05) para el número de botones y el rendimiento de campo.  El mayor rendimiento de algodón-semilla y fibra fue mostrado por el tratamiento testigo con 5.370,7 kg ha-1 y 2.028,3 kg ha-1, respectivamente. Cabe destacar que el tratamiento de 40.000 plantas.ha-1 presentó rendimientos similares con 5.137,4 kg ha-1 de algodón-semilla y 1.986,7 kg ha-1 de fibra, habiendo diferencia numérica pero no estadística (P>0,05) entre ello

Compactifications of the Klebanov-Witten CFT and new AdS 3 backgrounds

In this paper we find various new backgrounds in Type IIB, IIA and M-theory with an $AdS_3$-factor. The solutions are smooth and preserve small amounts of SUSY. These new backgrounds are found by application of non-Abelian T-duality (sometimes combined with T-duality) on the supergravity solution dual to the Klebanov-Witten CFT compactified to two dimensions. The field theory aspects encoded by these backgrounds are studied. We give a detailed account of conserved charges, central charges, entanglement entropy and Wilson loops. Further, we present a possible field theory interpretation for our backgrounds.Comment: 38 pages plus appendices, 6 figure

The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations

Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk\u27s mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ~7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet–disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules