| 1. |
- Blåbäck, Johan, et al.
(författare)
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BPS domain walls from backreacted orientifolds
- 2014
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5, s. 040-
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Tidskriftsartikel (refereegranskat)abstract
- Compactifications with D-brane and orientifold sources lead to standard gauged supergravity theories if the sources are smeared over the internal directions. It is therefore of interest to find how the solutions described by the gauged supergravity are altered by properly localising the sources. In this paper we analyse this for BPS domain wall solutions in the seven-dimensional gauged supergravity obtained from an O6 toroidal orientifold in massive IIA supergravity. This is one of the simplest no-scale supergravities that can be constructed and analysed in full detail. We find the BPS domain walls when the O6 planes are smeared. When the O6 planes are localised the domain wall solutions live in a warped compactification and we present the first-order equations these domain walls obey in 10 dimensions. In order to get explicit expressions we also consider the non-compact versions of the solutions for which the O6 planes have been traded for D6 branes and we recover the gauged supergravity expressions for the domain walls in the leading terms of the warp factor. Through T-duality we obtain partially localised solutions for compactifications to four dimensions using O3 planes with 3-form fluxes.
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| 2. |
- Barack, Leor, et al.
(författare)
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Black holes, gravitational waves and fundamental physics : a roadmap
- 2019
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 36:14
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Forskningsöversikt (refereegranskat)abstract
- The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.
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| 3. |
- Giri, Suvendu, 1988-
(författare)
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New horizons in string theory : bubble babble in search of darkness
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It was discovered nearly two decades ago that we live in an accelerating universe that is dominated by dark energy. Understanding the origin of such an energy has turned out to be a very difficult open question in physics, and calls on the need for a fundamental theory like string theory. However, despite decades-long effort, string theory has proven incredibly resilient to a satisfactory construction of dark energy within its framework.In the first part of this thesis and the included papers, we examine this problem and propose two possible solutions. The first is a construction within the framework of M-theory, the eleven dimensional cousin of string theory. Using only well-understood geometric ingredients and higher-derivative corrections to eleven dimensional supergravity, we present a new class of four dimensional vacua that contain dark energy. In the process, we also construct a new class of non-supersymmetric Minkowski vacua that were previously not known. Our second idea is a novel proposal that our universe could be embedded on the surface of an enormous spherical bubble that is expanding in a five dimensional anti de Sitter spacetime. The bubble is made of branes in string theory and its expansion is driven by the difference in the cosmological constants across it. We argued that such a construction arises naturally in string theory, and showed how four dimensional gravity arises in such a universe. We further showed that four dimensional matter and radiation arise from quantities that are innately five dimensional.Another challenging problem in physics concerns the nature of black holes – the presence of an event horizon in particular. This poses a paradox between well understood physical principles, and requires a fundamental theory for its resolution. Towards this goal, we constructed a novel class of horizonless objects that mimics black holes, and proposed these objects as an alternative end point of gravitational collapse. Subsequently, we constructed slowly rotating versions of these "black shells" and proposed an observational signature that could distinguish them from black holes in cosmological experiments. This is discussed in the second part of the thesis and in the included papers.
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| 4. |
- Perz, Jan, et al.
(författare)
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Black holes, first-order flow equations and geodesics on symmetric spaces
- 2009
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Ingår i: Fortschritte der Physik. - : Wiley. - 0015-8208 .- 1521-3978. ; 57:5-7, s. 659-665
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Tidskriftsartikel (refereegranskat)abstract
- For both extremal and non-extremal spherically symmetric black holes in theories with massless scalars and vectors coupled to gravity, we derive a general form of first-order gradient flow equations, equivalent to the equations of motion. For theories that have a symmetric moduli space after a dimensional reduction over the timelike direction, we discuss the condition for such a gradient flow to exist.
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