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Sökning: L773:0264 9381 > Koivisto Tomi S.

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1.
  • Jimenez, Jose Beltran, et al. (författare)
  • Extended Gauss-Bonnet gravities in Weyl geometry
  • 2014
  • Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 31:13, s. 135002-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we consider an extended Gauss-Bonnet gravity theory in arbitrary dimensions and in a space provided with a Weyl connection, which is torsion-free but non-metric-compatible, the non-metricity tensor being determined by a vector field. The action considered consists of the usual Einstein-Hilbert action plus all the terms quadratic in the curvature that reduce to the usual Gauss-Bonnet term for vanishing Weyl connection, i.e., when only the Levi-Civita part of the connection is present. We expand the action in terms of Riemannian quantities and obtain vector-tensor theories. We find that all the free parameters only appear in the kinetic term of the vector field, so two branches are possible: one with a propagating vector field and another one where the vector field does not propagate. We focus on the propagating case. We find that in four dimensions, the theory is equivalent to Einstein's gravity plus a Proca field. This field is naturally decoupled from matter, so it represents a natural dark matter candidate. Also for d = 4, we discuss a non-trivial cubic term in the curvature that can be constructed without spoiling the second-order nature of the field equations, because it leads to the vector-tensor Horndeski interaction. In arbitrary dimensions, the theory becomes more involved. We show that, even though the vector field presents kinetic interactions which do not have U(1) symmetry, there are no additional propagating degrees of freedom with respect to the usual massive case. We show that, interestingly, this relies on the fact that the corresponding Stuckelberg field belongs to a specific class within the general Horndeski theories. Finally, since Weyl geometries provide the natural ground on which to build scale invariant theories, we apply the usual Weyl gauging in order to make the Horndeski action locally scale invariant, and discuss new terms that can be added.
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2.
  • Zlosnik, Tom, et al. (författare)
  • Spacetime and dark matter from spontaneous breaking of Lorentz symmetry
  • 2018
  • Ingår i: Classical and quantum gravity. - : Institute of Physics (IOP). - 0264-9381 .- 1361-6382. ; 35:23
  • Tidskriftsartikel (refereegranskat)abstract
    • It is shown that a spontaneously-broken gauge theory of the Lorentz group contains Ashtekar's chiral formulation of general relativity accompanied by dust. From this perspective, gravity is described entirely by a connection omega valued in the Lie algebra of the complexified Lorentz group and a Lorentz-charged scalar field tau. The model is 'pre-geometric' in the sense that the spacetime metric may be constructed only in the symmetry-broken regime. We speculate on the extent to which this dust may account for dark matter and on the behaviour of the theory in regimes where the symmetry is not broken.
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  • Resultat 1-2 av 2
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tidskriftsartikel (2)
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refereegranskat (2)
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Jimenez, Jose Beltra ... (1)
Zlosnik, Tom (1)
Urban, Federico (1)
Marzola, Luca (1)
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Kungliga Tekniska Högskolan (2)
Stockholms universitet (2)
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Engelska (2)
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Naturvetenskap (2)

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