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  • 1.
    Ashoorioon, Amjad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Sheikh-Jabbari, M. M.
    1/N resolution to inflationary eta-problem2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 713, no 4-5, p. 353-357Article in journal (Refereed)
    Abstract [en]

    We observe that the dominant one loop contribution to the graviton propagator in the theory of N (N >> 1) light scalar fields phi(a) (with masses smaller than M-pI/root N) minimally coupled to Einstein gravity is proportional to N while that of graviton-scalar-scalar interaction vertex is N independent. We use this to argue that the coefficient of the R phi(2)(a) term appearing at one loop level is 1/N suppressed. This observation provides a resolution to the quantum eta-problem, that the slow-roll parameter eta receives order one quantum loop corrections for inflationary models built within the framework of scalar fields minimally coupled to Einstein gravity, for models involving large number of fields. As particular examples, we employ this to argue in favor of the absence of eta-problem in multi-field inflationary scenarios of M-flation and N-flation.

  • 2.
    Banerjee, Souvik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Giri, Suvendu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Schillo, Marjorie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    De Sitter cosmology on an expanding bubble2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 164Article in journal (Refereed)
    Abstract [en]

    Constructing an explicit compactification yielding a metastable de Sitter (dS) vacuum in a UV consistent string theory is an incredibly difficult open problem. Motivated by this issue, as well as the conjecture that all non-supersymmetric AdS vacua must decay, we discuss the alternative possibility of realizing an effective four-dimensional dS cosmology on a codimension-one bubble wall separating two AdS(5) vacua. The construction further elaborates on the scenario of , where the aforementioned cosmology arises due to a non-perturbative decay and is embedded in a five-dimensional bulk in a time- dependent way. In this paper we discuss the relation between this scenario and the weak gravity conjecture and further develop the details of the four-dimensional cosmology. We provide a bulk interpretation for the dS temperature as the Unruh temperature experienced by an accelerated observer riding the bubble. A source of four-dimensional matter arises from a string cloud in the bulk, and we examine the consequences for the particle mass spectrum. Furthermore, we show how effective four-dimensional Einstein gravity on the bubble is obtained from the five-dimensional Gauss equation. We conclude by outlining some implications that this paradigm will have for holography, inflation, the standard model, and black holes.

  • 3.
    Banerjee, Souvik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Giri, Suvendu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Schillo, Marjorie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Emergent de Sitter cosmology from decaying Anti-de Sitter Space2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 26, article id 261301Article in journal (Refereed)
    Abstract [en]

    Recent developments in string compactifications demonstrate obstructions to the simplest constructions of low energy cosmologies with positive vacuum energy. The existence of obstacles to creating scale-separated de Sitter solutions indicates a UV/IR puzzle for embedding cosmological vacua in a unitary theory of quantum gravity. Motivated by this puzzle, we propose an embedding of positive energy Friedmann-Lemaitre-Robertson-Walker cosmology within string theory. Our proposal involves confining 4D gravity on a brane which mediates the decay from a nonsupersymmetric five-dimensional anti-de Sitter false vacuum to a true vacuum. In this way, it is natural for a 4D observer to experience an effective positive cosmological constant coupled to matter and radiation, avoiding the need for scale separation or a fundamental de Sitter vacuum.

  • 4. Bena, I.
    et al.
    Blåbäck, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Van Riet, T.
    Antibranes cannot become black2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 10, p. 104023-Article in journal (Refereed)
    Abstract [en]

    When D-branes are inserted in flux backgrounds of opposite charge, the resulting solution has a certain singularity in the fluxes. Recently it has been argued, using numerical solutions, that for anti-D3 branes in the Klebanov-Strassler background, these singularities cannot be cloaked by a horizon, which strongly suggests they are not physical. In this paper we provide an analytic proof that the singularity of all codimension-three antibrane solutions (such as anti-D6 branes in massive type IIA supergravity or anti-D3 branes smeared on the T-3 of R-3 x T-3 with fluxes) cannot be hidden behind a horizon and that the charge of black branes with smooth event horizons must have the same sign as the charge of the flux background. Our result indicates that infinitesimally blackening the antibranes immediately triggers brane-flux annihilation and strengthens the intuition that antibranes placed in flux with positive charge immediately annihilate against it.

  • 5. Bergstrom, Lars
    et al.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Can MAP and Planck map Planck physics?2002In: JHEP, Vol. 12, p. 038-Article in journal (Refereed)
  • 6.
    Blaback, Johan
    et al.
    Univ Roma Tor Vergata, Dipartimento Fis, Via Ric Sci 1, I-00133 Rome, Italy;Univ Roma Tor Vergata, Sez INFN, Via Ric Sci 1, I-00133 Rome, Italy.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Giri, Suvendu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Constructing stable de Sitter in M-theory from higher curvature corrections2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 042Article in journal (Refereed)
    Abstract [en]

    We consider dimensional reductions of M-theory on T-7/Z(2)(3) with the inclusion of arbitrary metric flux and spacetime filling KK monopoles. With these ingredients at hand, we are able to construct a novel family of non-supersymmetric yet tachyon free Minkowski extrema. These solutions are supported by pure geometry with no extra need for gauge fluxes and possess a fully stable perturbative mass spectrum, up to a single flat direction. Such a direction corresponds to the overall internal volume, with respect to which the scalar potential exhibits a no-scale behavior. We then provide a mechanism that lifts the flat direction to give it a positive squared mass while turning Mkw(4) into dS(4). The construction makes use of the combined effect of G(7) flux and higher curvature corrections. Our solution is scale separated and the quantum corrections are small. Finally we speculate on novel possibilities when it comes to scale hierarchies within a given construction of this type, and possible issues with the choice of quantum vacuum.

  • 7.
    Blabaeck, J.
    et al.
    Univ Paris Saclay, Inst Phys Theor, CEA, CNRS, F-91191 Gif Sur Yvette, France..
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vargas, Sergio. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Universal dS vacua in STU-models2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 069Article in journal (Refereed)
    Abstract [en]

    Stable de Sitter solutions in minimal F-term supergravity are known to lie close to Minkowski critical points. We consider a class of STU-models arising from type IIB compactifications with generalised fluxes. There, we apply an analytical method for solving the equations of motion for the moduli fields based on the idea of treating derivatives of the superpotential of different orders up to third as independent objects. In particular, supersymmetric and no-scale Minkowski solutions are singled out by physical reasons. Focusing on the study of dS vacua close to supersymmetric Minkowski points, we are able to elaborate a complete analytical treatment of the mass matrix based on the sGoldstino bound. This leads to a class of interesting universal dS vacua. We finally explore a similar possibility around no-scale Minkowski points and discuss some examples.

  • 8. Blåbäck, Johan
    et al.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    A new light on the darkest corner of the landscape2018In: Article in journal (Refereed)
    Abstract [en]

    otivated by the recently proposed bounds on the slow-roll parameters forscalar potentials arising from string/M-theory compactifications, a.k.a. theRefined de Sitter Swampland conjecture, we explore the sharpness of suchconstraints within 4D supergravities coming from compactifications of massivetype IIA string theory onT6/(Z2×Z2). With the aid of a numerical technique,known as differential evolution, we are able to find a de Sitter extremum whichis fully metastable up to one single flat direction. This solution is supported byspacetime filling sources such as O6 planes and KK monopoles. Our exampleviolates the bound imposed by this conjecture

  • 9.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Accelerated Universes from type IIA Compactifications2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 003Article in journal (Other academic)
    Abstract [en]

    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

  • 10.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Fully stable dS vacua from generalised fluxes2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 8, p. 054-Article in journal (Refereed)
    Abstract [en]

    We investigate the possible existence of (meta-)stable de Sitter vacua within \cN=1 compactifications with generalised fluxes. With the aid of an algorithm inspired by the method of differential evolution, we were able to find three novel examples of completely tachyon-free de Sitter extrema in a non-isotropic type IIB model with non-geometric fluxes. We also analyse the surroundings of the aforementioned points in parameter space and chart the corresponding stability regions. These happen to occur at small values of the cosmological constant compared to the AdS scale.

  • 11.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Junghans, D.
    Van Riet, T.
    Vargas, Sergio C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Localised anti-branes in non-compact throats at zero and finite T2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, article id 018Article in journal (Refereed)
    Abstract [en]

    We investigate the 3-form singularities that are typical to anti-brane solutions in supergravity and check whether they can be cloaked by a finite temperature horizon. For anti-D3-branes in the Klebanov-Strassler background, this was already shown numerically to be impossible when the branes are partially smeared. In this paper, we present analytic arguments that also localised branes remain with singular 3-form fluxes at both zero and finite temperature. These results may have important, possibly fatal, consequences for constructions of meta-stable de Sitter vacua through uplifting.

  • 12.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Junghans, Daniel
    Van Riet, Thomas
    Wrase, Timm
    Zagermann, Marco
    (Anti-)brane backreaction beyond perturbation theory2012In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2012, no 2, p. 025-Article in journal (Refereed)
    Abstract [en]

    We improve on the understanding of the backreaction of anti-D6-branes in a flux background that is mutually BPS with D6-branes. This setup is analogous to the study of the backreaction of anti-D3-branes inserted in the KS throat, but does not require us to smear the anti-branes or do a perturbative analysis around the BPS background. We solve the full equations of motion near the anti-D6-branes and show that only two boundary conditions are consistent with the equations of motion. Upon invoking a topological argument we eliminate the boundary condition with regular H flux since it cannot lead to a solution that approaches the right kind of flux away from the anti-D6-branes. This leaves us with a boundary condition which has singular, but integrable, H flux energy density.

  • 13.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Junghans, Daniel
    Van Riet, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Wrase, Timm
    Zagermann, Marco
    The problematic backreaction of SUSY-breaking branes2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, p. 105-Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate the localisation of SUSY-breaking branes which, in the smeared approximation, support specific non-BPS vacua. We show, for a wide class of boundary conditions, that there is no flux vacuum when the branes are described by a genuine delta-function. Even more, we find that the smeared solution is the unique solution with a regular brane profile. Our setup consists of a non-BPS AdS(7) solution in massive IIA supergravity with smeared anti-D6-branes and fluxes T-dual to ISD fluxes in IIB supergravity.

  • 14.
    Blåbäck, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Van Riet, Thomas
    Resolving anti-brane singularities through time-dependence2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, p. 61-Article in journal (Refereed)
    Abstract [en]

    In this note we discuss a possible resolution of the flux singularities associated with the insertion of branes in backgrounds supported by fluxes that carry charges opposite to the branes. We present qualitative arguments that such a setup could be unstable both in the closed and open string sector. The singularities in the fluxes then get naturally resolved by taking the true solution to be a time-dependent process in which flux gets attracted towards the brane and subsequently annihilates.In this note we discuss a possible resolution of the flux singularities associated with the insertion of branes in backgrounds supported by fluxes that carry charges opposite to the branes. We present qualitative arguments that such a setup could be unstable both in the closed and open string sector. The singularities in the fluxes then get naturally resolved by taking the true solution to be a time-dependent process in which flux gets attracted towards the brane and subsequently annihilates.

  • 15. Brecher, Dominic
    et al.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Gregory, James P.
    Olsson, Martin E.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Rotating black holes in a Goedel universe2003In: JHEP, Vol. 11, p. 033-Article in journal (Refereed)
  • 16.
    Carlson, Karin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology. Earth Sciences, Department of Earth Sciences, Air and Water Science. Physics, Department of Physics and Materials Science, Theoretical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology. Mathematics and Computer Science, Department of Mathematics, Mathematics I -V.
    Kiselman, Christer
    Earth Sciences, Department of Earth Sciences, Air and Water Science. Physics, Department of Physics and Materials Science, Theoretical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology. Mathematics and Computer Science, Department of Mathematics, Mathematics I -V.
    Danielsson, Ulf
    Department of Theoretical Physics. Earth Sciences, Department of Earth Sciences, Air and Water Science. Physics, Department of Physics and Materials Science, Theoretical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology. Mathematics and Computer Science, Department of Mathematics, Mathematics I -V.
    Halldin, Sven
    Earth Sciences, Department of Earth Sciences, Air and Water Science. Physics, Department of Physics and Materials Science, Theoretical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology. Mathematics and Computer Science, Department of Mathematics, Mathematics I -V.
    Mattsson, Amalia
    Language policy for a bilingual faculty2005In: Bi- and multilingual universities, Helsinki, Finland, Sept 1-3, 2005, 2005Conference paper (Refereed)
    Abstract [en]

    The Faculty of Science and Technology of Uppsala University is for all practical purposes a bilingual institution, using both Swedish and English in education and research. Extensive use of English in teaching, and also in intrauniversity communication, permits recruitment of nonSwedishspeaking students, researchers and professors, and also prepares our students for

    international careers. However, the introduction of English has been somewhat haphazard, not taking into account possible negative effects on communication in Swedish, nor on students'

    learning.

    In order to improve students' and professors' language skills, and achieve a good balance between Swedish and English, the faculty board appointed a language committee in 2003 whose task was to propose a language policy for the faculty. A first part, stating as a main goal that all communication from and within the faculty should have the highest quality possible, has been adopted by the board. A second part including language planning with respect to status, corpus, and acquisition for both Swedish and English to accomplish this goal was sent to the board of the faculty in May, 2005. Implementation of this policy will affect all faculty activities, especially education. Suggested

    annual reports on language status will raise our present minimal knowledge about possible domain losses and allow for relevant countermeasures.

  • 17.
    Chialva, Diego
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Danielsson, Ulf H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Johansson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Theoretical Physics, Theoretical Physics.
    Larfors, Magdalena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Vonk, Marcel
    IHES.
    Deforming, revolving and resolving: New paths in the string theory landscape2008In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 02, article id 016Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate the properties of series of vacua in the string theory landscape. In particular, we study minima to the flux potential in type IIB compactifications on the mirror quintic. Using geometric transitions, we embed its one-dimensional complex structure moduli space in that of another Calabi-Yau with h1,1 = 86 and h2,1 = 2. We then show how to construct infinite series of continuously connected minima to the mirror quintic potential by moving into this larger moduli space, applying its monodromies, and moving back. We provide an example of such series, and discuss their implications for the string theory landscape

  • 18.
    Danielsson, U
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Goobar, A
    Nilsson, B
    String theory and cosmology: proceedings of Nobel symposium 127, Sigtuna, Sweden, August 14-19, 20032005Book (Other scientific)
  • 19.
    Danielsson, U.H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Shiu, G.
    Van Riet, T.
    Wrase, T.
    A note on obstinate tachyons in classical dS solutions2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, p. 138-Article in journal (Refereed)
    Abstract [en]

    The stabilisation of the dilaton and volume in tree-level flux compactifications leads to model independent and thus very powerful existence and stability criteria for dS solutions. In this paper we show that the sizes of cycles wrapped by orientifold planes are scalars whose scalings in the potential are not entirely model independent, but enough to entail strong stability constraints. For all known dS solutions arising from massive IIA supergravity flux compactifications on SU(3)-structure manifolds the tachyons are exactly within the subspace spanned by the dilaton, the total volume and the volumes of the orientifold cycles. We illustrate this in detail for the well-studied case of the O6 plane compactification on SU(2)xSU(2)/Z_2xZ_2. For that example we uncover another novel structure in the tachyon spectrum: the dS solutions have a singular, but supersymmetric, Minkowski limit, in which the tachyon exactly aligns with the sgoldstino.

  • 20.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Theoretical Physics.
    1905 - Einsteins fantastiska år2005In: Uppsala Nya Tidning, Vol. 2005, no 2005-02-27Article in journal (Other (popular scientific, debate etc.))
  • 21.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    A black hole hologram in de Sitter space2002In: JHEP, Vol. 03, p. 020-Article in journal (Refereed)
  • 22.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    A matrix model black hole: Act II2004In: JHEP, Vol. 02, p. 067-Article in journal (Refereed)
  • 23.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    A note on inflation and transplanckian physics2002In: Phys. Rev., Vol. D66, p. 023511-Article in journal (Refereed)
  • 24.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Can Planck see transplanck?2003In: Beyond '03, Schloss Ringberg, June 2003., 2003Conference paper (Other scientific)
  • 25.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Det yppersta om universum i ett nötskal2002In: Dagens forskning, Vol. 2002, no 2Article in journal (Other (popular scientific, debate etc.))
  • 26.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    En visionär fyller 100 år2004In: Populär Astronomi, Vol. 2004, no 2Article in journal (Other (popular scientific, debate etc.))
  • 27.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Holography, inflation, and quantum fluctuations in the early universe2003In: JCAP, Vol. 0303, p. 002-Article in journal (Refereed)
  • 28.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Högskoleverket har ansvar för understimulans2002In: Dagens Nyheter, no 2002-09-08Article in journal (Other (popular scientific, debate etc.))
  • 29.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Inflation as a probe of new physics2006In: Journal of Cosmology and Astroparticle Physics, Vol. 03, no 014Article in journal (Refereed)
  • 30.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Inflation, holography and the choice of vacuum in de Sitter space2002In: JHEP, Vol. 07, p. 040-Article in journal (Refereed)
  • 31.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Introduction to string theory2001In: Rept. Prog. Phys., Vol. 64, p. 51-96Article in journal (Refereed)
  • 32.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Kvantmekanikens absoluta slump2001In: Forskning och framsteg, Vol. 2001, no 3Article in journal (Other (popular scientific, debate etc.))
  • 33.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Lectures on string theory and cosmology2005In: Classical and Quantum Gravity, Vol. 22, p. S1-S40Article in journal (Refereed)
    Abstract [en]

    In these lectures I review recent attempts to apply string theory to cosmology, including string cosmology and various models of brane cosmology. In addition, the review includes an introduction to inflation as well as a discussion of transplanckian signatures. I also provide a critical discussion of the possible role of holography. The material is based on lectures given in January 2004 at the RTN String School in Barcelona, but also contain some additional material.

  • 34.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Något om strängteori2005In: Hjärnstorm, Vol. 85/86Article in journal (Other (popular scientific, debate etc.))
  • 35.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    On the consistency of de Sitter vacua2002In: JHEP, Vol. 12, p. 025-Article in journal (Refereed)
  • 36.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Perturbative decay of anti-branes in flux backgrounds due to space time instabilities2015Article in journal (Refereed)
    Abstract [en]

    In this paper we suggest a new source of perturbative decay of the KPV-state, which might have consequences for the viability of the KKLT-construction. The results do not rely on any direct enhancement of the decay due to flux accumulating on the anti-brane in transverse space. Instead, we note that the system can lower its energy through a sequence of NS5-configurations all the way to the true vacuum, without encountering a barrier, if we allow for clumping of screened charge in space time. The clumping can possibly be a parallel to the Gregory-Laflamme instability of black branes. The results are obtained at large pp, but for p/MpM arbitrarily small. It is furthermore argued that the results extend to cases of few or single anti-branes where quantization becomes important. We believe that it is important to investigate this possible effect further to judge whether there are any fatal consequences.

  • 37.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Physik für Poeten: von Sternschnuppen, schwarzen Löchern und anderen Merkwürdigkeiten im Universum2004Book (Other (popular scientific, debate etc.))
  • 38.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Planckian physics in the sky2004In: Proceedings of the Gunnar Nordström Symposium on Theoretical Physics, 2004, p. 43-63Conference paper (Other scientific)
  • 39.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Quantum gravitational proton decay at high temperature2005Other (Other scientific)
    Abstract [en]

    One of the most important challenges of contemporary physics is to find experimental signatures of quantum gravity. It is expected that quantum gravitational effects lead to proton decay but on time scales way beyond what is of any relevance to experiments. At non-zero temperatures there are reasons to believe that the situation is much more favourable. We will argue that at the temperatures and densities reached at present and future fusion facilities there is a realistic possibility that proton decay could be detectable.

  • 40.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Stjerner og epler som faller: en bok om oppdagelser og merkverdigheter i universet2005Book (Other (popular scientific, debate etc.))
  • 41.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Stjärnor och äpplen som faller: en bok om upptäckter och märkvärdigheter i universum2004Book (Other (popular scientific, debate etc.))
  • 42.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Stjärnor och äpplen som faller: en bok om upptäckter och märkvärdigheter i universum2003Book (Other (popular scientific, debate etc.))
  • 43.
    Danielsson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    The quantum swampland2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 095Article in journal (Refereed)
    Abstract [en]

    In this paper we propose a quantum version of the swampland conjecture. We argue that quantum instabilities of de Sitter space discovered using field theoretical methods, are directly related to the difficulties in finding stringy de Sitter vacua.

  • 44.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Till strängteorins försvar2004In: Forskning och framsteg, Vol. 2004, no 8Article in journal (Other (popular scientific, debate etc.))
  • 45.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Tomheten rymmer mer än man kan ana2001In: Svenska Dagbladet, no 2001-06-05Article in journal (Other (popular scientific, debate etc.))
  • 46.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics. Department of Physics and Materials Science, Theoretical Physics.
    Transplanckian energy production and slow roll inflation2005In: Physical Review D, Vol. 71, p. 023516-Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate how the energy density due to a non-standard choice of initial vacuum affects the expansion of the universe during inflation. To do this we introduce source terms in the Friedmann equations making sure that we respect the relation between gravity and thermodynamics. We find that the energy production automatically implies a slow rolling cosmological constant. Hence we also conclude that there is no well defined value for the cosmological constant in the presence of sources. We speculate that a non-standard vacuum can provide slow roll inflation on its own.

  • 47.
    Danielsson, Ulf
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Theoretical Physics.
    Är Big Bang bara en av många ursmällar?2003In: Dagens forskning, Vol. 2003, no 1Article in journal (Other (popular scientific, debate etc.))
  • 48.
    Danielsson, Ulf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    An alternative to anti-branes and O-planes?2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, p. 013-Article in journal (Refereed)
    Abstract [en]

    In this paper we consider type IIA compactifications in the isotropic Z(2) x Z(2) orbifold with a flux-induced perturbative superpotential combined with non-perturbative effects. Without requiring the presence of O-planes, and simply having D6-branes as local sources, we demonstrate the existence of de Sitter (dS) critical points, where the non-perturbative contributions to the cosmological constant have negligible size. We note, however, that these solutions generically have tachyons. By means of a more systematic search, we are able to find two examples of stable dS vacua with no need for anti-branes or O-planes, which, however, exhibit important non-perturbative corrections. The examples that we present turn out to remain stable even after opening up the fourteen non-isotropic moduli.

  • 49.
    Danielsson, Ulf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Fate of stringy AdS vacua and the weak gravity conjecture2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 96, no 2, article id 026020Article in journal (Refereed)
    Abstract [en]

    Ooguri and Vafa [arXiv:1610.015313] have recently proposed a stronger version of the weak gravity conjecture (WGC), based on which they concluded that all those nonsupersyrrurietric AdS vacua that can be embedded within a consistent theory of quantum gravity necessarily develop instabilities. In this paper we further elaborate on this proposal by arguing that the aforementioned instabilities have a perturbative nature and arise from the crucial interplay between the closed and the open string sectors of the theory.

  • 50.
    Danielsson, Ulf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Dibitetto, Giuseppe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Geometric non-geometry2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 084Article in journal (Refereed)
    Abstract [en]

    We consider a class of (orbifolds of) M-theory compactifications on S-d x T7-d with gauge fluxes yielding minimally supersymmetric STU-models in 4D. We present a group-theoretical derivation of the corresponding flux-induced superpotentials and argue that the aforementioned backgrounds provide a (globally) geometric origin for 4D theories that only look locally geometric from the perspective of twisted tori. In particular, we show that Q-flux can be used to generate compactifications on S-4 x T-3. We thus conclude that the effect of turning on non-geometric fluxes, at least when the section condition is solved, may be recovered by considering reductions on different topologies other than toroidal.

12 1 - 50 of 80
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