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- Albornoz, N. L. Gonzalez, et al.
(författare)
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Dark matter scenarios with multiple spin-2 fields
- 2018
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP PUBLISHING LTD. - 1475-7516. ; :1
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Tidskriftsartikel (refereegranskat)abstract
- We study ghost-free multimetric theories for (N + 1) tensor fields with a coupling to matter and maximal global symmetry group S-N x (Z(2))(N). Their mass spectra contain a massless mode, the graviton, and N massive spin-2 modes. One of the massive modes is distinct by being the heaviest, the remaining (N - 1) massive modes are simply identical copies of each other. All relevant physics can therefore be understood from the case N = 2. Focussing on this case, we compute the full perturbative action up to cubic order and derive several features that hold to all orders in perturbation theory. The lighter massive mode does not couple to matter and neither of the massive modes decay into massless gravitons. We propose the lighter massive particle as a candidate for dark matter and investigate its phenomenology in the parameter region where the matter coupling is dominated by the massless graviton. The relic density of massive spin-2 can originate from a freeze-in mechanism or from gravitational particle production, giving rise to two different dark matter scenarios. The allowed parameter regions are very different from those in scenarios with only one massive spin-2 field and more accessible to experiments.
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| 2. |
- Torsello, Francesco
(författare)
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Symmetries and black holes in Hassan–Rosen bimetric theory
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Hassan–Rosen bimetric theory is an extension of general relativity which considers the interaction between two metric fields defined on the same differentiable manifold. Self-accelerating cosmologies are exact solutions of this theory, and this makes it interesting to explore. We analyze the theory and see if it can provide other physically consistent solutions.Despite the effort put in studying the theory in recent years, very few exact solutions are known in the literature, and the majority are equivalent to those of general relativity. A valuable approach to try to simplify the field equations and find exact solutions is to impose some spacetime symmetry on the system, e.g., spherical symmetry.Our study is concerned with symmetries of spacetimes in Hassan–Rosen bimetric theory. Two metrics being present, we investigate what relations exist between their spacetime symmetries. We focus on the isometries of the metrics and clarify when they are the same.We apply the results in exploring solutions in the Hassan–Rosen theory. We consider maximally symmetric solutions and black hole solutions, and find a previously unknown class of non-stationary spherically symmetric solutions. The existence of the class of non-stationary spherically symmetric solutions disproof a similar statement to Birkhoff's theorem in the Hassan–Rosen bimetric theory. The study of bidiagonal non-rotating black holes sharing the isometries focuses on their properties both at the shared Killing horizon and far from it.The thesis is a review of these results, and the relevant papers accompany it.
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