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Strings, Gravitons, and Effective Field Theories
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns a range of aspects of theoretical physics. It is composed of two parts. In the first part we motivate our line of research, and introduce and discuss the relevant concepts. In the second part, four research papers are collected. The first paper deals with a possible extension of general relativity, namely the recently discovered classically consistent bimetric theory. In this paper we study the behavior of perturbations of the metric(s) around cosmologically viable background solutions. In the second paper, we explore possibilities for particle physics with low-scale supersymmetry. In particular we consider the addition of supersymmetric higher-dimensional operators to the minimal supersymmetric standard model, and study collider phenomenology in this class of models. The third paper deals with a possible extension of the notion of Lie algebras within category theory. Considering Lie algebras as objects in additive symmetric ribbon categories we define the proper Killing form morphism and explore its role towards a structure theory of Lie algebras in this setting. Finally, the last paper is concerned with the computation of string amplitudes in four dimensional models with reduced supersymmetry. In particular, we develop general techniques to compute amplitudes involving gauge bosons and gravitons and explicitly compute the corresponding three- and four-point functions. On the one hand, these results can be used to extract important pieces of the effective actions that string theory dictates, on the other they can be used as a tool to compute the corresponding field theory amplitudes.

Abstract [en]

Over the last twenty years there have been spectacular observations and experimental achievements in fundamental physics. Nevertheless all the physical phenomena observed so far can still be explained in terms of two old models, namely the Standard Model of particle physics and the ΛCDM cosmological model. These models are based on profoundly different theories, quantum field theory and the general theory of relativity. There are many reasons to believe that the SM and the ΛCDM are effective models, that is they are valid at the energy scales probed so far but need to be extended and generalized to account of phenomena at higher energies. There are several proposals to extend these models and one promising theory that unifies all the fundamental interactions of nature: string theory.

With the research documented in this thesis we contribute with four tiny drops to the filling of the fundamental physics research pot. When the pot will be saturated, the next fundamental discovery will take place.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2016. , 57 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2016:30
Keyword [en]
string theory, amplitudes, supersymmetry, particle phenomenology, BMSSM, modified gravity, bimetric, massive gravity, Lie algebras, ribbon categories
National Category
Other Physics Topics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-41912ISBN: 978-91-7063-708-7 (print)OAI: oai:DiVA.org:kau-41912DiVA: diva2:925036
Public defence
2016-06-03, 21A342, Karlstad University, Karlstad, 13:00 (English)
Opponent
Supervisors
Available from: 2016-05-13 Created: 2016-04-25 Last updated: 2016-05-13Bibliographically approved
List of papers
1. Growth Histories in Bimetric Massive Gravity
Open this publication in new window or tab >>Growth Histories in Bimetric Massive Gravity
Show others...
2012 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 12Article in journal (Refereed) Published
Abstract [en]

We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity.

Place, publisher, year, edition, pages
Bristol: IoP Publishing, 2012
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-26948 (URN)10.1088/1475-7516/2012/12/021 (DOI)000312959800021 ()
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2017-12-06Bibliographically approved
2. Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM
Open this publication in new window or tab >>Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM
2013 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 2Article in journal (Refereed) Published
Abstract [en]

We show that supersymmetric ‘‘new physics’’ beyond the minimal supersymmetric standard model can naturally accommodate a Higgs mass near 126 GeV and enhance the signal rate in the h to gamma gamma channel, while the signal rates in all the other Higgs decay channels coincide with Standard Model expectations, except possibly the h to Z gamma channel. The new physics that corrects the relevant Higgs couplings can be captured by two supersymmetric effective operators. We provide a simple example of an underlying model in which these operators are simultaneously generated. The scale of new physics that generates these operators can be around 5 TeV or larger, and outside the reach of the LHC.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2013
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-30079 (URN)10.1103/PhysRevD.88.025017 (DOI)000321738200011 ()
External cooperation:
Available from: 2013-11-21 Created: 2013-11-21 Last updated: 2017-12-06Bibliographically approved
3. On the Killing form of Lie Algebras in Symmetric Ribbon Categories
Open this publication in new window or tab >>On the Killing form of Lie Algebras in Symmetric Ribbon Categories
2015 (English)In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 11, 017Article in journal (Refereed) Published
Abstract [en]

As a step towards the structure theory of Lie algebras in symmetric monoidal categories we establish results involving the Killing form. The proper categorical setting for discussing these issues are symmetric ribbon categories.

Place, publisher, year, edition, pages
NATL ACAD SCI UKRAINE, 2015
Keyword
Lie algebra, monoidal category, Killing form, Lie superalgebra
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-41659 (URN)10.3842/SIGMA.2015.017 (DOI)000350561700001 ()
Available from: 2016-04-11 Created: 2016-04-11 Last updated: 2017-11-30Bibliographically approved
4. From maximal to minimal supersymmetry in string loop amplitudes
Open this publication in new window or tab >>From maximal to minimal supersymmetry in string loop amplitudes
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 163Article in journal (Refereed) Published
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-41950 (URN)10.1007/JHEP04(2017)163 (DOI)
Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2017-10-30Bibliographically approved

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