| 1. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Comments on the paper ‘Static solutions of the Vlasov–Einstein system’ by G. Wolansky
- 2020
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Ingår i: Archive for Rational Mechanics and Analysis. - : Springer Science and Business Media LLC. - 1432-0673 .- 0003-9527. ; 235:1, s. 783-791
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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. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Existence of axially symmetric static solutions of the Einstein-Vlasov system
- 2011
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Ingår i: Commun. Math. Phys.. - : Springer Science and Business Media LLC. - 0010-3616 .- 1432-0916. ; 308, s. 23-47
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Tidskriftsartikel (refereegranskat)abstract
- We prove the existence of static, asymptotically flat non-vacuum spacetimes with axial symmetry where the matter is modeled as a collisionless gas. The axially symmetric solutions of the resulting Einstein-Vlasov system are obtained via the implicit function theorem by perturbing off a suitable spherically symmetric steady state of the Vlasov-Poisson system.
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| 3. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Global existence for the spherically symmetric Einstein-Vlasov system with outgoing matter
- 2008
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Ingår i: Communications in Partial Differential Equations. - : Informa UK Limited. - 0360-5302 .- 1532-4133. ; 33:4, s. 656-668
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Tidskriftsartikel (refereegranskat)abstract
- We prove a new global existence result for the asymptotically flat, spherically symmetric Einstein-Vlasov system which describes in the framework of general relativity an ensemble of particles which interact by gravity. The data are such that initially all the particles are moving radially outward and that this property can be bootstrapped. The resulting non-vacuum spacetime is future geodesically complete.
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| 5. |
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| 6. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Gravitational collapse and the formation of black holes for the spherically symmetric Einstein-Vlasov system.
- 2010
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Ingår i: Quarterly of Applied Mathematics. - 1552-4485. ; 68, s. 17-42
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Tidskriftsartikel (refereegranskat)abstract
- We review results on the spherically symmetric, asymptotically flat Einstein-Vlasov system. We focus on a recent result where we found explicit conditions on the initial data which guarantee the formation of a black hole in the evolution. Among these data there are data such that the corresponding solutions exist globally in Schwarzschild coordinates. We put these results into a more general context, and we include arguments which show that the spacetimes we obtain satisfy the weak cosmic censorship conjecture and contain a black hole in the sense of suitable mathematical definitions of these concepts which are available in the literature.
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| 7. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Rotating, Stationary, Axially Symmetric Spacetimes with Collisionless Matter
- 2014
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Ingår i: Communications in Mathematical Physics. - : Springer Science and Business Media LLC. - 0010-3616 .- 1432-0916. ; 329:2, s. 787-808
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Tidskriftsartikel (refereegranskat)abstract
- The existence of stationary solutions to the Einstein–Vlasov system which are axially symmetric and have non-zero total angular momentum is shown. This pro- vides mathematical models for rotating, general relativistic and asymptotically flat non- vacuum spacetimes. If angular momentum is allowed to be non-zero, the system of equations to solve contains one semilinear elliptic equation which is singular on the axis of rotation. This can be handled very efficiently by recasting the equation as one for an axisymmetric unknown on R 5.
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| 8. |
- Andreasson, Håkan, 1966, et al.
(författare)
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STATIC SOLUTIONS TO THE SPHERICALLY SYMMETRIC EINSTEIN-VLASOV SYSTEM: A PARTICLE NUMBER-CASIMIR APPROACH
- 2023
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Ingår i: SIAM Journal on Mathematical Analysis. - 1095-7154 .- 0036-1410. ; 55:5, s. 4843-4879
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Tidskriftsartikel (refereegranskat)abstract
- The existence of nontrivial static spherically symmetric solutions to the Einstein- Vlasov system is well-known. However, it is an open problem whether or not static solutions arise as minimizers of a variational problem. Apart from being of interest in its own right, it is the connection to nonlinear stability that gives this topic its importance. This problem was considered in [G. Wolansky, Arch. Ration. Mech. Anal., 156 (2001), pp. 205-230], but as has been pointed out in [H. Andr\'easson and M. Kunze, Arch. Ration. Mech. Anal., 235 (2020), pp. 783-791], that paper contained serious flaws. In this work we construct static solutions by solving the Euler- Lagrange equation for the energy density ρ as a fixed point problem. The Euler-Lagrange equation originates from the particle number-Casimir functional introduced in Wolansky (2001). We then define a density function f on phase space which induces the energy density \rho and we show that it constitutes a static solution of the Einstein-Vlasov system. Hence we settle rigorously parts of what Wolansky (2001) attempted to prove.
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| 9. |
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| 10. |
- Barucca, G., et al.
(författare)
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Study of excited Ξ baryons with the P¯ ANDA detector
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
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Tidskriftsartikel (refereegranskat)abstract
- The study of baryon excitation spectra provides insight into the inner structure of baryons. So far, most of the world-wide efforts have been directed towards N∗ and Δ spectroscopy. Nevertheless, the study of the double and triple strange baryon spectrum provides independent information to the N∗ and Δ spectra. The future antiproton experiment P¯ANDA will provide direct access to final states containing a Ξ¯ Ξ pair, for which production cross sections up to μb are expected in p¯p reactions. With a luminosity of L= 10 31 cm- 2 s- 1 in the first phase of the experiment, the expected cross sections correspond to a production rate of ∼106events/day. With a nearly 4 π detector acceptance, P¯ANDA will thus be a hyperon factory. In this study, reactions of the type p¯p → Ξ¯ +Ξ∗ - as well as p¯p → Ξ¯ ∗ +Ξ- with various decay modes are investigated. For the exclusive reconstruction of the signal events a full decay tree fit is used, resulting in reconstruction efficiencies between 3 and 5%. This allows high statistics data to be collected within a few weeks of data taking.
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