A new form of the rotating C-metric

In a previous paper, we showed that the traditional form of the charged C-metric can be transformed, by a change of coordinates, into one with an explicitly factorizable structure function. This new form of the C-metric has the advantage that its properties become much simpler to analyze. In this paper, we propose an analogous new form for the rotating charged C-metric, with structure function G(\xi)=(1-\xi^2)(1+r_{+}A\xi)(1+r_{-}A\xi), where r_\pm are the usual locations of the horizons in the Kerr-Newman black hole. Unlike the non-rotating case, this new form is not related to the traditional one by a coordinate transformation. We show that the physical distinction between these two forms of the rotating C-metric lies in the nature of the conical singularities causing the black holes to accelerate apart: the new form is free of torsion singularities and therefore does not contain any closed timelike curves. We claim that this new form should be considered the natural generalization of the C-metric with rotation.Comment: 13 pages, LaTe

Pair of accelerated black holes in an anti-de Sitter background: the AdS C-metric

The anti-de Sitter C-metric (AdS C-metric) is characterized by a quite interesting new feature when compared with the C-metric in flat or de Sitter backgrounds. Indeed, contrarily to what happens in these two last exact solutions, the AdS C-metric only describes a pair of accelerated black holes if the acceleration parameter satisfies A>1/L, where L is the cosmological length. The two black holes cannot interact gravitationally and their acceleration is totally provided by the pressure exerted by a strut that pushes the black holes apart. Our analysis is based on the study of the causal structure, on the description of the solution in the AdS 4-hyperboloid in a 5D Minkowski embedding spacetime, and on the physics of the strut. We also analyze the cases A=1/L and A<1/L that represent a single accelerated black hole in the AdS background.Comment: 20 pages, 15 figures (RevTeX4). Published version: typo in fig. 5 corrected, references adde

Melvin universe as a limit of the C-metric

It is demonstrated that the Melvin universe representing the spacetime with a strong 'homogeneous' electric field can by obtained from the spacetime of two accelerated charged black holes by a suitable limiting procedure. The behavior of various invariantly defined geometrical quantities in this limit is also studied.Comment: 5 pages, no figures [v2: two references added

Boost-rotation symmetric type D radiative metrics in Bondi coordinates

The asymptotic properties of the solutions to the Einstein-Maxwell equations with boost-rotation symmetry and Petrov type D are studied. We find series solutions to the pertinent set of equations which are suitable for a late time descriptions in coordinates which are well adapted for the description of the radiative properties of spacetimes (Bondi coordinates). By calculating the total charge, Bondi and NUT mass and the Newman-Penrose constants of the spacetimes we provide a physical interpretation of the free parameters of the solutions. Additional relevant aspects on the asymptotics and radiative properties of the spacetimes considered, such as the possible polarization states of the gravitational and electromagnetic field, are discussed through the way

Radiation from accelerated black holes in an anti-de Sitter universe

We study gravitational and electromagnetic radiation generated by uniformly accelerated charged black holes in anti-de Sitter spacetime. This is described by the C-metric exact solution of the Einstein-Maxwell equations with a negative cosmological constant Lambda. We explicitly find and interpret the pattern of radiation that characterizes the dependence of the fields on a null direction from which the (timelike) conformal infinity is approached. This directional pattern exhibits specific properties which are more complicated if compared with recent analogous results obtained for asymptotic behavior of fields near a de Sitter-like infinity. In particular, for large acceleration the anti-de Sitter-like infinity is divided by Killing horizons into several distinct domains with a different structure of principal null directions, in which the patterns of radiation differ.Comment: 19 pages, 11 colour figures, submitted to Phys. Rev. D [Low quality figures are included in this version because of arXive size restrictions. The version with the standard quality figures is available at http://utf.mff.cuni.cz/~podolsky/jppubl.htm.

Growth performance and gut health parameters of finishing broilers supplemented with plant extracts and exposed to daily increased temperature

The effects of three plant extracts, i.e. lemon peel extract (LPE), orange peel extract (OPE) and Curcuma xanthorrhiza essential oil (CXEO), on the performance and gut health parameters of broilers exposed to high temperature was investigated. A total of 336 unsexed Ross 308 broilers were distributed to seven dietary treatments, a control diet and six diets containing 200 or 400 mg kg�1 feed of one of the three products between d 25-38 (12 chicks per pen, four replicates). To induce chronic heat stress, the temperature was increased to 34°C with 50% relative humidity for 5 h daily starting from d 28 until d 38. At d 38, four animals per pen were sampled for morphological characteristics (duodenum, jejunum and ileum) and microbial counts (ileo-cecal contents). Plant extracts did not affect the bird performance. The bursa weight of the control birds was lower (p < 0.05) comparing to those fed 400 mg kg�1 OPE and 200 and 400 mg kg�1 CXEO diets. Feeding 400 mg kg�1 of LPE decreased the duodenal villus:crypt ratio compared to control and 200 mg kg�1 OPE fed birds. Plant extracts did not have effect on ileal histo-morphology. Feeding with 400 mg kg�1 of LPE and CXEO caused a decrease in coliform counts in ileum and feeding of 400 mg kg�1 CXEO diet decreased coliform counts in caecum compared to control birds (p < 0.05). These results elucidate that CXEO, OPE and LPE might modify some microbial and intestinal traits, but without beneficial effect on performance of broilers under heat stress