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Träfflista för sökning "WFRF:(Andreasson Håkan 1966 ) "

Sökning: WFRF:(Andreasson Håkan 1966 )

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1.
  • Andréasson, Håkan, 1955-, et al. (författare)
  • Comments on the paper ‘Static solutions of the Vlasov–Einstein system’ by G. Wolansky
  • 2019
  • Ingår i: Archive for Rational Mechanics and Analysis. - 1432-0673 .- 0003-9527.
  • Tidskriftsartikel (refereegranskat)abstract
    • In this note we address the attempted proof of the existence of static solutions to the Einstein–Vlasov system as given in Wolansky (Arch Ration Mech Anal 156:205–230, 2001). We focus on a specific and central part of the proof which concerns a variational problem with an obstacle. We show that two important claims in Wolansky (2001) are incorrect and we question the validity of a third claim. We also discuss the variational problem and its difficulties with the aim of stimulating further investigation of this intriguing problem in particular answering the question of whether or not static solutions of the Einstein–Vlasov system can be found as local minimizers of an energy-Casimir functional.
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2.
  • Ames, E., et al. (författare)
  • Cosmic string and black hole limits of toroidal Vlasov bodies in general relativity
  • 2019
  • Ingår i: Physical Review D. - 2470-0010. ; 99:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We numerically investigate limits of a two-parameter family of stationary solutions to the Einstein-Vlasov system. The solutions are toroidal and have nonvanishing angular momentum. As the parameters are tuned to more relativistic solutions (measured e.g., by an increasing redshift) we provide evidence for a sequence of solutions which approaches the extreme Kerr black hole family. Solutions with angular momentum larger than the square of the mass are also investigated, and in the relativistic limit the near-field geometry of such solutions is observed to become locally rotationally symmetric about the matter density. The existence of a deficit angle in these regions is investigated.
3.
  • Ames, Ellery, et al. (författare)
  • On axisymmetric and stationary solutions of the self-gravitating Vlasov system
  • 2016
  • Ingår i: Classical and Quantum Gravity. - 0264-9381. ; 33:15
  • Tidskriftsartikel (refereegranskat)abstract
    • Axisymmetric and stationary solutions are constructed to the Einstein-Vlasov and Vlasov-Poisson systems. These solutions are constructed numerically, using finite element methods and a fixed-point iteration in which the total mass is fixed at each step. A variety of axisymmetric stationary solutions are exhibited, including solutions with toroidal, disk-like, spindle-like, and composite spatial density configurations, as are solutions with non-vanishing net angular momentum. In the case of toroidal solutions, we show for the first time, solutions of the Einstein-Vlasov system which contain ergoregions.
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6.
  • Andreasson, Håkan, 1966-, et al. (författare)
  • A numerical investigation of the stability of steady states and critical phenomena for the spherically symmetric Einstein–Vlasov system
  • 2006
  • Ingår i: Classical and Quantum Gravity. ; 23, s. 3659-3677
  • Tidskriftsartikel (refereegranskat)abstract
    • The stability features of steady states of the spherically symmetric EinsteinVlasov system are investigated numerically. We find support for the conjecture by Zel'dovich and Novikov that the binding energy maximum along a steady state sequence signals the onset of instability, a conjecture which we extend to and confirm for non-isotropic states. The sign of the binding energy of a solution turns out to be relevant for its time evolution in general. We relate the stability properties to the question of universality in critical collapse and find that for Vlasov matter universality does not seem to hold.
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7.
  • Andreasson, Håkan, 1966-, et al. (författare)
  • A numerical investigation of the steady states of the spherically symmetric Einstein-Vlasov-Maxwell system
  • 2009
  • Ingår i: Classical and Quantum Gravity. - 0264-9381. ; 26:14
  • Tidskriftsartikel (refereegranskat)abstract
    • We construct, by numerical means, static solutions of the spherically symmetric Einstein-Vlasov-Maxwell system and investigate various features of the solutions. This extends a previous investigation (Andreasson and Rein 2007 Class. Quantum Grav. 24 1809) of the chargeless case. We study the possible shapes of the energy density profile as a function of the area radius when the electric charge of an individual particle is varied as a parameter. We find profiles which are multi-peaked, where the peaks are separated either by vacuum or a thin atmosphere, and we find that for a sufficiently large charge parameter the solutions break down at a finite radius. Furthermore, we investigate the inequality root M
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9.
  • Andreasson, Håkan, 1966- (författare)
  • Black hole formation from a complete past for the einstein–vlasov system
  • 2014
  • Ingår i: International conference on Relativity and Gravitation, 2012, Prague, Czech Republic, 25-29 June 2012. - 0930-8989 .- 1867-4941. - 978-3-319-06760-5 ; 157, s. 11-18
  • Konferensbidrag (refereegranskat)abstract
    • Anatural question in general relativity is to find initial data for the Einstein equations whose past evolution is regular and whose future evolution contains a black hole. In [1] initial data of this kind is constructed for the spherically symmetric Einstein–Vlasov system. One consequence of the result is that there exists a class of initial data for which the ratio of the Hawking mass (Formula presented) (r) and the area radius r is arbitrarily small everywhere, such that a black hole forms in the evolution. This result is analogous to the result [2] for a scalar field. Another consequence is that there exist black hole initial data such that the solutions exist for all Schwarzschild time t ∈ (−∞,∞). In the present article we review the results in [1].
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10.
  • Andreasson, Håkan, 1966- (författare)
  • Black Hole Formation from a Complete Regular Past for Collisionless Matter
  • 2012
  • Ingår i: Annales Henri Poincaré. - 1424-0637. ; 13:7, s. 1511-1536
  • Tidskriftsartikel (refereegranskat)abstract
    • Initial data for the spherically symmetric Einstein-Vlasov system is constructed whose past evolution is regular and whose future evolution contains a black hole. This is the first example of initial data with these properties for the Einstein-matter system with a "realistic" matter model. One consequence of the result is that there exists a class of initial data for which the ratio of the Hawking mass mIS= mIS (r) and the area radius r is arbitrarily small everywhere, such that a black hole forms in the evolution. This result is in a sense analogous to the result (Christodoulou Commun Pure Appl Math 44:339-373, 1991) for a scalar field. Another consequence is that there exist black hole initial data such that the solutions exist for all Schwarzschild time .
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