| 1. |
- Bundzik, Daniel, et al.
(författare)
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The geometry of fractional D1-branes
- 2004
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 1361-6382 .- 0264-9381. ; 21:16, s. 3985-3993
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Tidskriftsartikel (refereegranskat)abstract
- We find explicit solutions of type IIB string theory on R-4/Z(2) corresponding to the classical geometry of fractional D1-branes. From the supergravity solution obtained, we capture perturbative information about the running of the coupling constant and the metric on the moduli space of N = 4, D = 2 super Yang-Mills.
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| 2. |
- Edgar, Brian, 1945-, et al.
(författare)
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A local potential for the Weyl tensor in all dimensions
- 2004
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Ingår i: Classical and quantum gravity. - 0264-9381 .- 1361-6382. ; 21:22
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Tidskriftsartikel (refereegranskat)abstract
- In all dimensions n ≥ 4 and arbitrary signature, we demonstrate the existence of a new local potential - a double (2, 3)-form, Pabcde - for the Weyl curvature tensor Cabcd, and more generally for all tensors Wabcd with the symmetry properties of the Weyl tensor. The classical four-dimensional Lanczos potential for a Weyl tensor - a double (2, 1)-form, Habc - is proven to be a particular case of the new potential: its double dual.
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| 3. |
- Andersson, Fredrik, et al.
(författare)
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Existence of Lanczos potentials and superpotentials for the Weyl spinor/tensor
- 2001
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 18:12, s. 2297-2304
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Tidskriftsartikel (refereegranskat)abstract
- A new and concise proof of existence - emphasizing the very natural and simple structure - is given for the Lanczos spinor potential LABCA' of an arbitrary symmetric spinor WABCD defined by WABCD = 2?(AA' LBCD)A', this proof is easily translated into tensors in such a way that it is valid in four-dimensional spaces of any signature. In particular, this means that the Weyl spinor ?ABCD has Lanczos potentials in all spacetimes, and furthermore that the Weyl tensor has Lanczos potentials on all four-dimensional spaces, irrespective of signature. In addition, two superpotentials for WABCD are identified: the first TABCD (= T(ABC)D) is given by LABCA' = ?A'DTABCD, while the second HABA'B' (= H(AB)(A'B')) (which is restricted to Einstein spacetimes) is given by LABCA' = ? (AB' HBC)A'B'. The superpotential TABCD is used to describe the gauge freedom in the Lanczos potential.
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| 4. |
- Bergqvist, Göran, et al.
(författare)
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Algebraic Rainich theory and antisymmetrization in higher dimensions
- 2002
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 19:12, s. 3341-3355
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Tidskriftsartikel (refereegranskat)abstract
- The classical Rainich(-Misner-Wheeler) theory gives necessary and sufficient conditions on an energy-momentum tensor T to be that of a Maxwell field (a 2-form) in four dimensions. Via Einstein's equations, these conditions can be expressed in terms of the Ricci tensor, thus providing conditions for a spacetime geometry to be an Einstein-Maxwell spacetime. One of the conditions is that T2 is proportional to the metric, and it has previously been shown in arbitrary dimension that any tensor satisfying this condition is a superenergy tensor of a simple p-form. Here we examine algebraic Rainich conditions for general p-forms in higher dimensions and their relations to identities by antisymmetrization. Using antisymmetrization techniques we find new identities for superenergy tensors of these general (non-simple) forms, and we also prove in some cases the converse: that the identities are sufficient to determine the form. As an example we obtain the complete generalization of the classical Rainich theory to five dimensions.
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| 5. |
- Bergqvist, Göran, et al.
(författare)
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New electromagnetic conservation laws
- 2003
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 20:13, s. 2663-2668
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Tidskriftsartikel (refereegranskat)abstract
- The Chevreton superenergy tensor was introduced in 1964 as a counterpart, for electromagnetic fields, of the well-known Bel–Robinson tensor of the gravitational field. We here prove the unnoticed facts that, in the absence of electromagnetic currents, Chevreton's tensor (i) is completely symmetric, and (ii) has a trace-free divergence if the Einstein–Maxwell equations hold. It follows that the trace of the Chevreton tensor is a rank-2, symmetric, trace-free, conserved tensor, which is different from the energy–momentum tensor, and nonetheless can be constructed for any test Maxwell field or any Einstein–Maxwell spacetime.
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| 6. |
- Bergqvist, Göran, 1963-, et al.
(författare)
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Unique characterization of the Bel-Robinson tensor
- 2004
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 21:14, s. 3499-3503
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Tidskriftsartikel (refereegranskat)abstract
- We prove that a completely symmetric and trace-free rank-4 tensor is, up to sign, a Bel-Robinson-type tensor, i.e., the superenergy tensor of a tensor with the same algebraic symmetries as the Weyl tensor, if and only if it satisfies a certain quadratic identity. This may be seen as the first Rainich theory result for rank-4 tensors.
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| 7. |
- Evangelista, Gianpaolo
(författare)
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Data Analysis Methods for Non-Gaussian, Nonstationary and Nonlinear Features and their Application to VIRGO
- 2003
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 20:17, s. S915-S924
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Tidskriftsartikel (refereegranskat)abstract
- The commissioning of the VIRGO central interferometer occasioned the implementation and tests of various algorithms for the characterization of the non-Gaussianity, non-stationarity and non-linearity of the dark fringe data. This library of prototypes will serve as groundwork for the near commissioning of VIRGO (full scale). We make a summary of the activities on that subject including the description of the selected algorithms and some results obtained with the data of the engineering runs.
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| 8. |
- Evangelista, Gianpaolo
(författare)
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The Present Status of the VIRGO Central Interferometer
- 2002
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 19:7, s. 1421-1428
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Tidskriftsartikel (refereegranskat)abstract
- The VIRGO Central Interferometer (CITF) is a short suspended interferometer operated with the central area elements of the VIRGO detector. The main motivation behind the CITF is to allow the integration and debugging of a large part of the subsystems of VIRGO while the construction of the long arms of the antenna is being completed. This will permit a faster commissioning of the full-size antenna. In fact, almost all the main components of the CITF, with the exception of the large mirrors and a few other details, are the same as those to be used for the full-size detector. In this paper the present status of the VIRGO CITF is reported.
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| 9. |
- Herberthson, Magnus, 1963-
(författare)
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The gravitational dipole and explicit multipole moments of static axisymmetric spacetimes
- 2004
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 21:22, s. 5121-5138
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Tidskriftsartikel (refereegranskat)abstract
- The multipole moments of static axisymmetric asymptotically flat spacetimes are considered. The usual set of recursively defined tensors is replaced with one real-valued function m defined on R+ ∪ {0}, where the moments are given by the derivatives of m at 0. As examples of applications, we show that the Schwarzschild spacetime is the gravitational monopole and derive the metric for the gravitational dipole.
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| 10. |
- Karlovini, Max, et al.
(författare)
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Constructing stellar objects with multiple necks
- 2001
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 18:5, s. 817-832
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the construction of perfect fluid stellar objects having optical geometries with multiple necks corresponding to spatially closed unstable lightlike geodesics. We prove that physically reasonable equations of state can give rise to stellar equilibria with arbitrarily many necks. We also show how a first-order phase transition can give rise to quite pronounced secondary necks. The analysis is carried out using a modification of a recent dynamical systems formulation of the TOV equations due to Nilsson and Uggla. Our reformulation allows for a very general family of equations of state including, for example, phase transitions.
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