Compact Binary Merger Rate in Dark-Matter Spikes

Nowadays, the existence of supermassive black holes (SMBHs) in the center of galactic halos is almost confirmed. An extremely dense region referred to as dark-matter spike is expected to form around central SMBHs as they grow and evolve adiabatically. In this work, we calculate the merger rate of compact binaries in dark-matter spikes while considering halo models with spherical and ellipsoidal collapses. Our findings exhibit that ellipsoidal-collapse dark matter halo models can potentially yield the enhancement of the merger rate of compact binaries. Finally, our results confirm that the merger rate of primordial black hole binaries is consistent with the results estimated by the LIGO-Virgo detectors, while such results can not be realized for primordial black hole-neutron star binaries.Comment: 13 pages; 5 figures; references added, typos were fixe

Stabilization of Sand with Colloidal Nano-Silica Hydrosols

Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout

Yet Another Realization of Kerr/CFT Correspondence

The correspondence between the Kerr black hole and a boundary CFT has been conjectured recently. The conjecture has been proposed first only for the half of the CFT, namely for left movers. For right movers, the correspondence has been also found out through the suitable asymptotic boundary condition. However, the boundary conditions for these two studies are exclusive to each other. The boundary condition for left movers does not allow the symmetry of right movers, and vice versa. We propose new boundary condition which allows both of left and right movers.Comment: 6 pages, references adde

Play dough as an educational tool for visualization of complicated cerebral aneurysm anatomy

BACKGROUND: Imagination of the three-dimensional (3D) structure of cerebral vascular lesions using two-dimensional (2D) angiograms is one of the skills that neurosurgical residents should achieve during their training. Although ongoing progress in computer software and digital imaging systems has facilitated viewing and interpretation of cerebral angiograms enormously, these facilities are not always available. METHODS: We have presented the use of play dough as an adjunct to the teaching armamentarium for training in visualization of cerebral aneurysms in some cases. RESULTS: The advantages of play dough are low cost, availability and simplicity of use, being more efficient and realistic in training the less experienced resident in comparison with the simple drawings and even angiographic views from different angles without the need for computers and similar equipment. The disadvantages include the psychological resistance of residents to the use of something in surgical training that usually is considered to be a toy, and not being as clean as drawings or computerized images. CONCLUSION: Although technology and computerized software using the patients' own imaging data seems likely to become more advanced in the future, use of play dough in some complicated cerebral aneurysm cases may be helpful in 3D reconstruction of the real situation

Nonanticommutative superspace and N= 1/2 WZ model

In these proceedings we review the main results concerning superspace geometries with nonanticommutative spinorial variables and field theories formulated on them. In particular, we report on the quantum properties of the WZ model formulated in the N=1/2 nonanticommutative superspace.Comment: 9 pages, plain Latex, contribution to the proceedings of the Copenhagen RTN workshop, 15-20 September 200

New Attractors, Entropy Function and Black Hole Partition Function

By making use of the entropy function formalism we study the generalized attractor equations in the four dimensional N=2 supergravity in presence of higher order corrections. This result might be used to understand a possible ensemble one could associate to an extremal black hole.Comment: 20 pages, latex file, V2: minor corrections, typos corrected, Refs added, V3: the version appeared in JHE

Caustic avoidance in Horava-Lifshitz gravity

There are at least four versions of Horava-Lishitz gravity in the literature. We consider the version without the detailed balance condition with the projectability condition and address one aspect of the theory: avoidance of caustics for constant time hypersurfaces. We show that there is no caustic with plane symmetry in the absence of matter source if \lambda\ne 1. If \lambda=1 is a stable IR fixed point of the renormalization group flow then \lambda is expected to deviate from 1 near would-be caustics, where the extrinsic curvature increases and high-energy corrections become important. Therefore, the absence of caustics with \lambda\ne 1 implies that caustics cannot form with this symmetry in the absence of matter source. We argue that inclusion of matter source will not change the conclusion. We also argue that caustics with codimension higher than one will not form because of repulsive gravity generated by nonlinear higher curvature terms. These arguments support our conjecture that there is no caustic for constant time hypersurfaces. Finally, we discuss implications to the recently proposed scenario of ``dark matter as integration constant''.Comment: 19 pages; extended to general z \geq 3, typos corrected (v2); version accepted for publication in JCAP (v3

Black Holes in Ho\v{r}ava Gravity with Higher Derivative Magnetic Terms

We consider Horava gravity coupled to Maxwell and higher derivative magnetic terms. We construct static spherically symmetric black hole solutions in the low-energy approximation. We calculate the horizon locations and temperatures in the near-extremal limit, for asymptotically flat and (anti-)de Sitter spaces. We also construct a detailed balanced version of the theory, for which we find projectable and non-projectable, non-perturbative solutions.Comment: 17 pages. v2: Up to date with published version; some minor remarks and more reference

Two-charge small black hole entropy: String-loops and multi-strings

We investigate the inclusion of 10-dimensional string loop corrections to the entropy function of two-charge extremal small black holes of the heterotic string theory compactified on S^1 x T^5 and show that the entropy is given by \pi\sqrt{a q_1 q_2+b q_1} where q_1 and q_2 are the charges with q_1 >> q_2 >> 1 and a and b are constants. Incorporating certain multi-string states into the microstate counting, we show that the new statistical entropy is consistent with the macroscopic scaling for one and two units of momentum (winding) and large winding (momentum). We discuss our scaling from the point of view of related AdS_3 central charge and counting of chiral primaries in superconformal quantum mechanics as well.Comment: 18 page