| 1. |
- Blåbäck, Johan, et al.
(author)
-
Accelerated Universes from type IIA Compactifications
- 2014
-
In: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :003
-
Journal article (other academic/artistic)abstract
- We study slow-roll accelerating cosmologies arising from geometric compactifications of type IIA string theory on T^6/(Z_2 x Z_2). With the aid of a genetic algorithm, we are able to find quasi-de Sitter backgrounds with both slow-roll parameters of order 0.1
|
|
| 2. |
- Blåbäck, Johan, et al.
(author)
-
BPS domain walls from backreacted orientifolds
- 2014
-
In: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5, s. 040-
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Blåbäck, Johan, et al.
(author)
-
de Sitter vacua from nonperturbative flux compactifications
- 2014
-
In: Physical Review D. - 1550-7998 .- 1550-2368. ; 90:2, s. 024065-
-
Journal article (peer-reviewed)abstract
- In this work we present stable de Sitter solutions of =1 supergravity in a geometric type IIB duality frame with the addition of non-perturbative contributions. Contrary to the standard approach we retain the moduli dependence of both the tree level superpotential and its non-perturbative contribution. This provides the possibility for a single-step approach that stabilises all moduli simultaneously in a de Sitter vacuum. By means of a genetic algorithm we find explicit solutions where different scales are separated and hierarchies are investigated.
|
|
| 4. |
- Blåbäck, Johan
(author)
-
Note on M2-branes in opposite charge
- 2014
-
In: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:6, s. 065004-
-
Journal article (peer-reviewed)abstract
- The flux singularity that arises for branes in oppositely charged fluxes is a widely discussed issue and in this paper the problem is investigated further. New AdS world volume (anti-)M2-brane solutions are constructed using space-filling branes placed in fluxes of opposite dissolved charge that is opposite to that of the brane. A topological obstruction is derived to show how the singularity develops during localization of this solution and any similarly constructed solution. Furthermore it is shown that it is not possible to hide the singularity behind a horizon, which would have given credence to an M theory resolution.
|
|
| 5. |
- Blåbäck, Johan, 1985-
(author)
-
Singular Fluxes in Ten and Eleven Dimensions : Sources, Singularities, Fluxes and Spam
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- The energy content of our present universe is dominated by the dark-energy, or vacuum energy, which provides accelerated cosmic expansion. Dark energy has a possible effective explanation through a positive cosmological constant. The problem present in any fundamental theory is to explain the underlying dynamics of what gives rise to the cosmological constant.In string theory there are several scenarios that could give insight into what is behind the positive cosmological constant. One such construction uses anti-branes to achieve a net positive energy density of the vacuum. Anti-branes refers in this case to branes placed in a background with oppositely charged flux. As backreaction and localisation procedures are considered for anti-brane constructions a certain kind of singularity arise. This new type of singularity is present in the surrounding flux, which is not directly sourced by the brane.This thesis, and the works contained, considers several aspects of this type of singularity. The first such flux singularity were discovered for the anti-D3-branes, in which the approximations and assumptions of partial smearing and perturbative expansions are used. Included in this thesis are new anti-D6-brane solutions which are placed in oppositely charged flux. It is shown that after the anti-D6-branes are localised, they display the same type of singularity. The strength of this result lies in that it is possible to show the presence of the singularity beyond partial smearing and perturbative expansions. Similar to the anti-D6-brane solutions, new anti-M2-brane solutions are presented. These solutions are also argued to display the same type of singularity.The investigation into the presence of the singularity is just the first step. The second step is to deduce whether this singularity is acceptable and can somehow be resolved. Included in this thesis are two works that considers exactly this. One way of interpreting the singularity is through the absence of a no-force condition between the brane and the surrounding flux. This interpretation leads to the conclusion that the singularity is present due to the use of static Ansätze in a system that is inherently time dependent. Through an adiabatic approach it is here argued that this interpretation leads to a new type of instability.Another way of arguing for a possible resolution of this singularity is whether or not the singularity can be cloaked by an event horizon. This condition have been successful in other systems with singularities. It is argued in this thesis that it is not possible to hide the flux singularity behind a horizon. This leads to one out of two conclusions, either the condition is not a necessary one and the singularity can be resolved in a static manner, or the singularity does not have a resolution.To put these works in context the current singularities from anti-branes program is briefly reviewed to give a full overview of the current situation of these investigations.
|
|
