Backreaction of accreting matter onto a black hole in the Eddington-Finkelstein coordinates

We study backreaction of accreting matter onto a spherically symmetric black hole in a perturbative way, when accretion is in a quasi-steady state. General expressions for corrections to the metric coefficients are found in the Eddington-Finkelstein coordinates. It is shown that near the horizon of a black hole, independently of the form of the energy-momentum tensor, the leading corrections to the metric are of the Vaidya form. The relation to other solutions is discussed and particular examples are presented.Comment: 12 pages, v.2: references added, typos corrected, matches published versio

Ultra-hard fluid and scalar field in the Kerr-Newman metric

An analytic solution for the accretion of ultra-hard perfect fluid onto a moving Kerr-Newman black hole is found. This solution is a generalization of the previously known solution by Petrich, Shapiro and Teukolsky for a Kerr black hole. Our solution is not applicable for an extreme black hole due to violation of the test fluid approximation. We also present a stationary solution for a massless scalar field in the metric of a Kerr-Newman naked singularity.Comment: 9 pages, 3 figures, revtex4; v2: presentation improved, figures added, matches published versio

Global topological k-defects

We consider global topological defects in symmetry breaking models with a non-canonical kinetic term. Apart from a mass parameter entering the potential, one additional dimensional parameter arises in such models -- a ``kinetic'' mass. The properties of defects in these models are quite different from ``standard'' global domain walls, vortices and monopoles, if their kinetic mass scale is smaller than their symmetry breaking scale. In particular, depending on the concrete form of the kinetic term, the typical size of such a defect can be either much larger or much smaller than the size of a standard defect with the same potential term. The characteristic mass of a non-standard defect, which might have been formed during a phase transition in the early universe, depends on both the temperature of a phase transition and the kinetic mass.Comment: 7 pages, 3 figures; v2: references added, matches the published versio

Black holes in the presence of dark energy

The new, rapidly developing field of theoretical research --- studies of dark energy interacting with black holes (and, in particular, accreting onto black holes) --- is reviewed. The term `dark energy' is meant to cover a wide range of field theory models, as well as perfect fluids with various equations of state, including cosmological dark energy. Various accretion models are analyzed in terms of the simplest test field approximation or by allowing back reaction on the black-hole metric. The behavior of various types of dark energy in the vicinity of Schwarzschild and electrically charged black holes is examined. Nontrivial effects due to the presence of dark energy in the black hole vicinity are discussed. In particular, a physical explanation is given of why the black hole mass decreases when phantom energy is being accreted, a process in which the basic energy conditions of the famous theorem of nondecreasing horizon area in classical black holes are violated. The theoretical possibility of a signal escaping from beneath the black hole event horizon is discussed for a number of dark energy models. Finally, the violation of the laws of thermodynamics by black holes in the presence of noncanonical fields is considered.Comment: 25 pages, 10 figures, review pape

Radial fall of a test particle onto an evaporating black hole

A test particle falling into a classical black hole crosses the event horizon and ends up in the singularity within finite eigentime. In the `more realistic' case of a `classical' evaporating black hole, an observer falling onto a black hole observes a sudden evaporation of the hole. This illustrates the fact that the discussion of the classical process commonly found in the literature may become obsolete when the black hole has a finite lifetime. The situation is basically the same for more complex cases, e.g. where a particle collides with two merging black holes. It should be pointed out that the model used in this paper is mainly of academic interest, since the description of the physics near a black hole horizon still presents a difficult problem which is not yet fully understood, but our model provides a valuable possibility for students to enter the interesting field of black hole physics and to perform numerical calculations of their own which are not very involved from the computational point of view.Comment: 6 pages, 3 figures, LATE

The Using of Biclustering Techniques in Inductive Modeling Systems of Biological Processes

In article studied the possibility using of bicluster analysis in clustering systems of complex biological nature objects. Biclustering was performed by use the algorithm BCCC of package "biclust" of software environment R, clustering of objects in each bicluster was performed by use the algorithm SOTA. The ratio of the average Euclidean distance between objects in different clusters and individual cluster accordingly were used as the criterion for an estimation of quality clustering.Досліджена можливість застосування бікластерного аналізу в системах кластеризації об'єктів складної біологічної природи. Бікластерізація проводилася за алгоритмом ВССС пакету "biclust" програмного середовища R, кластеризація об'єктів в бікластерах проводилася за алгоритмом SOTA. Критерієм оцінки якості кластеризації було відношення середньої евклідової відстані між об'єктами в різних кластерах і в окремих кластерах відповідно.Исследована возможность применения бикластерного анализа в системах кластеризации объектов сложной биологической природы. Бикластеризация проводилась с использованием алгоритма ВССС пакета “biclust” програмной среды R, кластеризация объектов в бикластерах производилась с использованием алгоритма SOTA. В качестве критерия оценки качества кластеризации использовалось отношение среднего евклидового расстояния между объектами в разных кластерах и в отдельных кластерах соответственно

Gravitational radiation from rotating monopole-string systems

We study the gravitational radiation from a rotating monopole-antimonopole pair connected by a string. While at not too high frequencies the emitted gravitational spectrum is described asymptotically by $P_n\propto n^{-1}$, the spectrum is exponentially suppressed in the high-frequency limit, $P_n\propto \exp(-n/n_{\rm cr})$. Below $n_{\rm cr}$, the emitted spectrum of gravitational waves is very similar to the case of an oscillating monopole pair connected by a string, and we argue therefore that the spectrum found holds approximately for any moving monopole-string system. As application, we discuss the stochastic gravitational wave background generated by monopole-antimonopole pairs connected by strings in the early Universe and gravitational wave bursts emitted at present by monopole-string networks. We confirm that advanced gravitational wave detectors have the potential to detect a signal for string tensions as small as $G\mu\sim 10^{-13}$.Comment: 8 pages, 2 figures, revtex4; v2: minor corrections, matches published versio

Recovering General Relativity from massive gravity

We obtain static, spherically symmetric, and asymptotically flat numerical solutions of massive gravity with a source. Those solutions show, for the first time explicitly, a recovery of the Schwarzschild solution of General Relativity via the so-called Vainshtein mechanism.Comment: 4 pages, 3 figures; v2: minor changes, matches published versio