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Institution

Center for Theoretical Physics

FacilityWarsaw, Poland
About: Center for Theoretical Physics is a facility organization based out in Warsaw, Poland. It is known for research contribution in the topics: Gamma-ray burst & Accretion (astrophysics). The organization has 68 authors who have published 112 publications receiving 1086 citations. The organization is also known as: Centrum Fizyki Teoretycznej PAN & Centrum Fizyki Teoretycznej Polskiej Akademii Nauk.


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Journal ArticleDOI
TL;DR: In this paper, the authors discuss two important instability mechanisms that may lead to the limit-cycle oscillations of the luminosity of the accretion disks around compact objects: ionization instability and radiation pressure instability.
Abstract: We discuss two important instability mechanisms that may lead to the limit-cycleoscillations of the luminosity of the accretion disks around compact objects: ionizationinstability and radiation-pressure instability. Ionization instability is well establishedas a mechanism of X-ray novae eruptions in black hole binary systems but its ap-plicability to AGN is still problematic. Radiation pressure theory has still very weakobservational background in any of these sources. In the present paper we attempt toconfront the parameter space of these instabilities with the observational data. At thebasis of this simple survey of sources properties we argue that the radiation pressureinstability is likely to be present in several Galactic sources with the Eddington ratiosabove 0.15, and in AGN with the Eddington ratio above 0.025. Our results favor theparameterization of the viscosity through the geometrical mean of the radiation andgas pressure both in Galactic sources and AGN. More examples of the quasi-regularoutbursts in the timescales of 100 seconds in Galactic sources, and hundreds of yearsin AGN are needed to formulate firm conclusions. We also show that the disk sizes inthe X-ray novae are consistent with the ionization instability. This instability may alsoconsiderably influence the lifetime cycle and overall complexity in the supermassiveblack hole environment.Keywords: physical processes:accretion; X-rays:binaries; galaxies: active – galaxies:evolution – galaxies

75 citations

Journal ArticleDOI
TL;DR: In this article, the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric is defined for a closed cosmological model with black holes as the only sources of the gravitational field.
Abstract: We discuss the continuum limit of the initial data for a vacuum, closed cosmological model with black holes as the only sources of the gravitational field. The model we consider is an exact solution of the constraint equations and represents a vacuum universe with a number of black holes placed on a spatial slice of S3 topology considered at the moment of its largest expansion when the black holes are momentary at rest. We explain how and under what conditions the Friedmann–Lemaitre–Robertson–Walker (FLRW) metric arises as the continuum limit when the number of black holes contained in the model goes to infinity. We also discuss the relation between the effective cosmological parameters of the model, inferred from the large scale geometry of the spacetime, and the masses of individual black holes. In particular, we prove an estimate for the difference between the total effective mass of the system and the sum of the masses of all black holes, thus quantifying the effects of the inhomogeneities in the matter distribution or the cosmological backreaction.

52 citations

Journal ArticleDOI
TL;DR: In this article, the existence of a wide range of highly entangled states of heterogeneous multipartite systems consisting of $N>2$ parties such that every reduction to one and two parties is maximally mixed.
Abstract: Heterogeneous bipartite quantum pure states, composed of two subsystems with a different number of levels, cannot have both reductions maximally mixed. In this work, we demonstrate existence of a wide range of highly entangled states of heterogeneous multipartite systems consisting of $N>2$ parties such that every reduction to one and two parties is maximally mixed. Two constructions of generating genuinely multipartite maximally entangled states of heterogeneous systems for an arbitrary number of subsystems are presented. Such states are related to quantum error correction codes over mixed alphabets and mixed orthogonal arrays. Additionally, we show the advantages of considering heterogeneous systems in practical implementations of multipartite steering.

49 citations

Journal ArticleDOI
TL;DR: In this paper, the asymptotic structure of the gravitational field at null infinity is re-examined by allowing certain potentials to develop "wire singularities" keeping the physical fields smooth.
Abstract: The asymptotic structure of the gravitational field at null infinity is re‐examined by allowing certain potentials to develop ‘‘wire singularities’’, keeping the physical fields smooth. This relaxation of the regularity conditions leads to the introduction of the Newman–Unti–Tamburino (NUT) 4‐momentum which is the ‘‘magnetic’’ or the ‘‘dual’’ counterpart of the Bondi–Sachs 4‐momentum. It is shown that, unlike the Bondi–Sachs 4‐momentum, the NUT 4‐vector is absolutely conserved even in the presence of gravitational radiation. Thus, while the gravitational field resembles the nonabelian Yang–Mills fields in its ‘‘electric’’ properties, it is analogous to the abelian Maxwell field in its ‘‘magnetic’’ properties. It is pointed out that gravitational fields with nonvanishing NUT 4‐momenta may have a substantial role in quantum gravity even though they are not physically significant in classical general relativity.

47 citations


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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20232
20228
20211
20201
201913
201819