On black holes in multidimensional theory with Ricci-flat internal spaces

A generalization of the Tangherlini solution for the case of n internal Ricci-flat spaces is obtained. It is shown that in the (2+d)-dimensional section a horizon exists only in the trivial case when the internal-space factors are constant. The p-adic analog of the solution is also considered.Comment: 6 pages, Late

How clonal is clonal? Genome plasticity across multicellular segments of a "candidatus marithrix sp." filament from sulfidic, briny seafloor sediments in the Gulf of Mexico

"Candidatus Marithrix" is a recently described lineage within the group of large sulfur bacteria (Beggiatoaceae, Gammaproteobacteria). This genus of bacteria comprises vacuolated, attached-living filaments that inhabit the sediment surface around vent and seep sites in the marine environment. A single filament is ca. 100 μm in diameter, several millimeters long, and consists of hundreds of clonal cells, which are considered highly polyploid. Based on these characteristics, "Candidatus Marithrix" was used as a model organism for the assessment of genomic plasticity along segments of a single filament using next generation sequencing to possibly identify hotspots of microevolution. Using six consecutive segments of a single filament sampled from a mud volcano in the Gulf of Mexico, we recovered ca. 90% of the "Candidatus Marithrix" genome in each segment. There was a high level of genome conservation along the filament with average nucleotide identities between 99.98 and 100%. Different approaches to assemble all reads into a complete consensus genome could not fill the gaps. Each of the six segment datasets encoded merely a few hundred unique nucleotides and 5 or less unique genes-the residual content was redundant in all datasets. Besides the overall high genomic identity, we identified a similar number of single nucleotide polymorphisms (SNPs) between the clonal segments, which are comparable to numbers reported for other clonal organisms. An increase of SNPs with greater distance of filament segments was not observed. The polyploidy of the cells was apparent when analyzing the heterogeneity of reads within a segment. Here, a strong increase in single nucleotide variants, or "intrasegmental sequence heterogeneity" (ISH) events, was observed. These sites may represent hotspots for genome plasticity, and possibly microevolution, since two thirds of these variants were not co-localized across the genome copies of the multicellular filament

On spherically symmetric minimally coupled brane worlds

For a static, spherically symmetric brane in the framework of the RS2 concept, we study the conditions under which the 4D tensor Eμν, arising from the 5D Weyl tensor, vanishes on the brane. Gravity on the brane is then decoupled from the bulk geometry, it is the so-called minimally coupled brane world (MCBW). Assuming Eμν = 0 in the whole bulk, we try to solve the 5D Einstein equations GAB + Λ5gAB = 0 and obtain an overdetermined set of equations for functions of the radial coordinate. Some special solutions are found, among which are the well-known "black string" solution with the Schwarzschild metric on the brane and its generalizations with Schwarzschild-(A)dS on-brane metrics. It is concluded that a MCBW can be embedded, in general, in a bulk where Eμ νis not identically zero but only vanishes on the brane. We also present some previous results on the general properties of scalar fields on the brane and give an example of a wormhole supported by a scalar field in a MCBW

Scalar field in a minimally coupled brane world: No-hair and other no-go theorems

In the brane-world framework, we consider static, spherically symmetric configurations of a scalar field with the Lagrangian (∂φ)2/2 - V (φ), confined on the brane. We use the 4D Einstein equations on the brane obtained by Shiromizu et al., containing the conventional stress tensor Tμ ν, the tensor IIμ ν which is quadratic in Tμ ν, and Eμ ν describing interaction with the bulk. For models under study, the tensor IIμ ν has zero divergence, allowing one to consider Eμ ν = 0. Such a brane, whose 4D gravity is decoupled from the bulk geometry, may be called minimally coupled. Assuming Eμ ν = 0, we try to extend to brane worlds some theorems valid for scalar fields in general relativity (GR). Thus, the list of possible global causal structures in all models under consideration is shown to be the same as is known for vacuum with a cosmological constant in GR: Minkowski, Schwarzschild, (anti-) de Sitter and Schwarzschild-(anti-)de Sitter. A no-hair theorem, saying that, given a potential V ≥ 0, asymptotically flat black holes cannot have nontrivial external scalar fields, is proved under certain restrictions. Some objects, forbidden in GR, are allowed on the brane, e.g, traversable wormholes supported by a scalar field, but only at the expense of enormous matter densities in the strong field region

On spherically symmetric minimally coupled brane worlds

For a static, spherically symmetric brane in the framework of the RS2 concept, we study the conditions under which the 4D tensor Eμν, arising from the 5D Weyl tensor, vanishes on the brane. Gravity on the brane is then decoupled from the bulk geometry, it is the so-called minimally coupled brane world (MCBW). Assuming Eμν = 0 in the whole bulk, we try to solve the 5D Einstein equations GAB + Λ5gAB = 0 and obtain an overdetermined set of equations for functions of the radial coordinate. Some special solutions are found, among which are the well-known "black string" solution with the Schwarzschild metric on the brane and its generalizations with Schwarzschild-(A)dS on-brane metrics. It is concluded that a MCBW can be embedded, in general, in a bulk where Eμ νis not identically zero but only vanishes on the brane. We also present some previous results on the general properties of scalar fields on the brane and give an example of a wormhole supported by a scalar field in a MCBW