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Phenomenological Studies in Cosmoparticle Physics: Expansion Histories in non-Einstein Gravity and Dark Matter at the Large Hadron Collider
Stockholm University, Faculty of Science, Department of Physics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the Big Bang model has become established, the fields of cosmology and particle physics have become intertwined. A range of observations forces us to consider the phenomena of dark matter and dark energy. This interpretation is based on our understanding of gravity, while the standard model of particle physics describes the other fundamental forces in nature and fails to explain the dark components. This thesis includes two different types of studies where hypotheses of physics beyond the standard models of particle physics and cosmology are faced with what observations and experiments can tell us.

The first one deals with the possibility that our theory of gravity is what has to be modified at large distances to explain the dark energy, which then need not be a contribution to the energy content at all. The expansion histories in two such frameworks are tested with data from type Ia supernovae and measurements of the baryon acoustic peak in the galaxy distribution as well as in the cosmic microwave background.

The second type of study concerns the possibility of establishing the particle nature of dark matter through interactions other than gravitational. While there are ways of doing this using astrophysical observations, the uncertainties due to astrophysics and the unknown distribution of the dark matter are large. High energy particle colliders provide a way of imitating the conditions of the early universe in the laboratory, where we can hope to produce yet unknown heavy particle states and in a more controlled environment determine their properties. We study the prospects for discovering two types of weakly interacting dark matter candidates at the CERN Large Hadron Collider.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholms University , 2011. , 48 p.
National Category
Natural Sciences
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-56952ISBN: 978-91-7447-302-5OAI: oai:DiVA.org:su-56952DiVA: diva2:414113
Public defence
2011-06-01, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript. Available from: 2011-05-10 Created: 2011-05-02 Last updated: 2011-05-03Bibliographically approved
List of papers
1. Testing the DGP Model with ESSENCE
Open this publication in new window or tab >>Testing the DGP Model with ESSENCE
2007 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 05, 003- p.Article in journal (Refereed) Published
Abstract [en]

We use the recent supernova data set from the ESSENCE collaboration combined with data from the Supernova Legacy Survey and nearby supernovae to test the Dvali–Gabadadze–Porrati (DGP) brane world model and its generalizations. Combination of these data with a flatness prior and the position of the peak of the cosmic microwave background (CMB) radiation disfavours the DGP model slightly. Inclusion of the baryon acoustic peak from the Sloan Digital Sky Survey increase the tension of the DGP model with the data, although it is not clear how self-consistent this procedure would be without a re-analysis of the survey data in the framework of the DGP cosmology. Generalizations of the DGP model are tested and constraints on relevant parameters obtained.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-12448 (URN)10.1088/1475-7516/2007/05/003 (DOI)000246851300019 ()
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2011-05-03Bibliographically approved
2. Expansion history and f(R) modified gravity
Open this publication in new window or tab >>Expansion history and f(R) modified gravity
2007 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 12, 005- p.Article in journal (Refereed) Published
Abstract [en]

We attempt to fit cosmological data using f(R) modified Lagrangians containing inverse powers of the Ricci scalar varied with respect to the metric. While we can fit the supernova data well, we confirm the behaviour at medium to high redshifts reported elsewhere and argue that the easiest way to show that this class of models are inconsistent with the data is by considering the thickness of the last scattering surface. For the best fit parameters to the supernova data, the simplest 1/R model gives rise to a last scattering surface of thickness Δz~530, inconsistent with observations.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-12508 (URN)10.1088/1475-7516/2007/12/005 (DOI)000251993400013 ()
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2011-05-03Bibliographically approved
3. Early Search for Supersymmetric Dark Matter Models at the LHC Without Missing Energy
Open this publication in new window or tab >>Early Search for Supersymmetric Dark Matter Models at the LHC Without Missing Energy
2010 (English)In: Journal of High Energy Physics (JHEP), ISSN 1029-8479, E-ISSN 1126-6708, no 3, 054- p.Article in journal (Refereed) Published
Abstract [en]

We investigate early discovery signals for supersymmetry at the Large Hadron Collider without using information about missing transverse energy. Instead we use cuts on the number of jets and isolated leptons (electrons and/or muons). We work with minimal supersymmetric extensions of the standard model, and focus on phenomenological models that give a relic density of dark matter compatible with the WMAP measurements. An important model property for early discovery is the presence of light sleptons, and we find that for an integrated luminosity of only 200–300 pb^{−1} at a center-of-mass energy of 10 TeV models with gluino masses up to ~700 GeV can be tested.

National Category
Subatomic Physics Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-39273 (URN)10.1007/JHEP03(2010)054 (DOI)000276798203005 ()
Available from: 2010-05-17 Created: 2010-05-17 Last updated: 2011-12-05Bibliographically approved
4. The inert doublet model and multilepton signatures at the LHC
Open this publication in new window or tab >>The inert doublet model and multilepton signatures at the LHC
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-56907 (URN)
Available from: 2011-05-02 Created: 2011-04-29 Last updated: 2011-05-11Bibliographically approved

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