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Danielsson, Ulf
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Publications (10 of 78) Show all publications
Blaback, J., Danielsson, U., Dibitetto, G. & Giri, S. (2019). Constructing stable de Sitter in M-theory from higher curvature corrections. Journal of High Energy Physics (JHEP) (9), Article ID 042.
Open this publication in new window or tab >>Constructing stable de Sitter in M-theory from higher curvature corrections
2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 042Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Flux compactifications, M-Theory
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-396631 (URN)10.1007/JHEP09(2019)042 (DOI)000489133700001 ()
Funder
Swedish Research Council
Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-08Bibliographically approved
Visinelli, L., Vagnozzi, S. & Danielsson, U. (2019). Revisiting a Negative Cosmological Constant from Low-Redshift Data. Symmetry, 11(8), Article ID 1035.
Open this publication in new window or tab >>Revisiting a Negative Cosmological Constant from Low-Redshift Data
2019 (English)In: Symmetry, ISSN 2073-8994, E-ISSN 2073-8994, Vol. 11, no 8, article id 1035Article in journal (Refereed) Published
Abstract [en]

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the ?CDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (i.e., maximally-symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state w phi on top. We test the consistency of the model against low-redshift baryon acoustic oscillation and Type Ia supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the Planck collaboration and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant and mild indications for an effective phantom dark energy component on top. A model comparison analysis reveals that the ?CDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should low-redshift tensions persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model by considering realistic string constructions.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
negative cosmological constant, H-0 tension, dark energy, low-redshift data, extended cosmological models
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-394165 (URN)10.3390/sym11081035 (DOI)000483559300066 ()
Funder
Swedish Research Council, 638-2013-8993Swedish Research Council, 2015-04814
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved
Danielsson, U. (2019). The quantum swampland. Journal of High Energy Physics (JHEP) (4), Article ID 095.
Open this publication in new window or tab >>The quantum swampland
2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 095Article in journal (Refereed) Published
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.

Keywords
Cosmology of Theories beyond the SM, Models of Quantum Gravity, Flux compactifications, Effective Field Theories
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-382845 (URN)10.1007/JHEP04(2019)095 (DOI)000465029400001 ()
Funder
Swedish Research Council
Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-05-23Bibliographically approved
Danielsson, U., Enberg, R., Ingelman, G. & Mandal, T. (2019). Varying gauge couplings and collider phenomenology. Physical Review D. Particles and fields, 100(5), Article ID 055028.
Open this publication in new window or tab >>Varying gauge couplings and collider phenomenology
2019 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 100, no 5, article id 055028Article in journal (Refereed) Published
Abstract [en]

In this paper we investigate a natural extension of the Standard Model that involves varying coupling constants. This is a general expectation in any fundamental theory such as string theory, and there are good reasons for why new physics could appear at reachable energy scales. We investigate the collider phenomenology of models with varying gauge couplings where the variations are associated with real singlet scalar fields. We introduce three different heavy scalar fields that are responsible for the variations of the three gauge couplings of the Standard Model. This gives rise to many interesting collider signatures that we explore, resulting in exclusion limits based on the most recent LHC data, and predictions of the future discovery potential at the high-luminosity LHC.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics; Theoretical Physics
Identifiers
urn:nbn:se:uu:diva-384700 (URN)10.1103/PhysRevD.100.055028 (DOI)000486644000010 ()
Funder
Swedish Research Council, 2015-04814
Available from: 2019-06-07 Created: 2019-06-07 Last updated: 2019-10-31Bibliographically approved
Blåbäck, J., Danielsson, U. & Dibitetto, G. (2018). A new light on the darkest corner of the landscape.
Open this publication in new window or tab >>A new light on the darkest corner of the landscape
2018 (English)In: Article in journal (Refereed) Epub ahead of print
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

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-371288 (URN)
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-04-25Bibliographically approved
Banerjee, S., Danielsson, U., Dibitetto, G., Giri, S. & Schillo, M. (2018). Emergent de Sitter cosmology from decaying Anti-de Sitter Space. Physical Review Letters, 121(26), Article ID 261301.
Open this publication in new window or tab >>Emergent de Sitter cosmology from decaying Anti-de Sitter Space
Show others...
2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 26, article id 261301Article in journal (Refereed) Published
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.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-371313 (URN)10.1103/PhysRevLett.121.261301 (DOI)000454433200002 ()30636156 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 113410212
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-01-15Bibliographically approved
Danielsson, U. H. & Giri, S. (2018). Observational signatures from horizonless black shells imitating rotating black holes. Journal of High Energy Physics (JHEP) (7), Article ID 070.
Open this publication in new window or tab >>Observational signatures from horizonless black shells imitating rotating black holes
2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 070Article in journal (Refereed) Published
Abstract [en]

In arXiv:1705.10172 it was proposed that string theory replaces Schwarzschild black holes with horizonless thin shells with an AdS interior. In this paper we extend the analysis to slowly rotating black holes, solving the Israel-Lanczos-Sen junction conditions for a rotating shell composed of stringy matter to determine the metric. Outside of the shell we find a vacuum solution that differs from Kerr with a 32% larger quadrupole moment. We discuss the observational consequences and explore the possibility to distinguish between a black shell and a black hole. Promising methods include imaging of the black hole at the center of the Milky Way using the Event Horizon Telescope, precision measurements of stars in close orbits around the central black hole, and future observations of colliding super massive black holes using the space based gravitational wave observatory LISA.

Place, publisher, year, edition, pages
SPRINGER, 2018
Keywords
Black Holes, Black Holes in String Theory, Classical Theories of Gravity
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-361272 (URN)10.1007/JHEP07(2018)070 (DOI)000438141900008 ()
Funder
Swedish Research Council
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2018-10-05Bibliographically approved
Danielsson, U. & Van Riet, T. (2018). What if string theory has no de Sitter vacua?. International Journal of Modern Physics D, 27(12), Article ID 1830007.
Open this publication in new window or tab >>What if string theory has no de Sitter vacua?
2018 (English)In: International Journal of Modern Physics D, ISSN 0218-2718, Vol. 27, no 12, article id 1830007Article, review/survey (Refereed) Published
Abstract [en]

We present a brief overview of attempts to construct de Sitter vacua in string theory and explain how the results of this 20-year endeavor could point to the fact that string theory harbors no de Sitter vacua at all. Making such a statement is often considered controversial and "bad news for string theory". We discuss how perhaps the opposite can be true.

Place, publisher, year, edition, pages
WORLD SCIENTIFIC PUBL CO PTE LTD, 2018
Keywords
String theory, low energy limit, de Sitter vacua
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-364832 (URN)10.1142/S0218271818300070 (DOI)000443732700001 ()
Funder
Swedish Research Council
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
Danielsson, U., Dibitetto, G. & Vargas, S. C. (2017). A swamp of non-SUSY vacua. Journal of High Energy Physics (JHEP), 2017(11), Article ID 152.
Open this publication in new window or tab >>A swamp of non-SUSY vacua
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2017, no 11, article id 152Article in journal (Refereed) Published
Abstract [en]

We consider known examples of non-supersymmetric AdS7 and AdS4 solutions arising from compactifications of massive type IIA supergravity and study their stability, taking into account the coupling between closed- and open-string sector excitations. Generically, open strings are found to develop modes with masses below the Breitenlohner-Freedman (BF) bound. We comment on the relation with the Weak Gravity Conjecture, and how this analysis may play an important role in examining the validity of non-supersymmetric constructions in string theory.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2017
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-341010 (URN)10.1007/JHEP11(2017)152 (DOI)000416355700006 ()
Funder
Swedish Research Council
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2018-07-31Bibliographically approved
Danielsson, U. H., Dibitetto, G. & Giri, S. (2017). Black holes as bubbles of AdS. Journal of High Energy Physics (JHEP) (10), Article ID 171.
Open this publication in new window or tab >>Black holes as bubbles of AdS
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 171Article in journal (Refereed) Published
Abstract [en]

In this paper we propose that bubbles of AdS within Minkowski spacetime, stabilized at a finite radius by stiff matter and an electromagnetic gas, can be an alternative endpoint of gravitational collapse. The bubbles are horizonless with a size up to 12.5% larger than their Schwarzschild radius depending on their charge. We argue that they are stable against small perturbations, and have thermodynamical properties similar to those of real black holes. We provide a realization of the bubbles within string theory that relies on a specific brane intersection giving rise to a shell carrying dissolved charges from lower dimensional D-branes as well as a gas of open strings. We also note that our construction provides a new way of understanding the entropy of Reissner-Nordstrom black holes in the extremal limit.

Place, publisher, year, edition, pages
SPRINGER, 2017
Keywords
Black Holes, Black Holes in String Theory, D-branes
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-340715 (URN)10.1007/JHEP10(2017)171 (DOI)000413665300001 ()
Funder
Swedish Research Council
Available from: 2018-02-02 Created: 2018-02-02 Last updated: 2018-02-02Bibliographically approved
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