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Phenomenology of Higgs Bosons Beyond the Standard Model
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

After a long history of searches, a Higgs boson H was discovered by the ATLAS and the CMS experiments at the Large Hadron Collider (LHC) in 2012. Its properties fit well the ones predicted by the Standard Model (SM) of particle physics. However, the SM can not explain other established properties of Nature, such as the existence of Dark Matter. For this reason, models beyond the SM should be considered. Such models often predict the existence of several Higgs bosons and this thesis explores some of those models. In particular, the possibility to discover a charged Higgs boson, which would be a clear sign of physics beyond the SM, is studied.

A commonly studied extension of the SM is the framework of two-Higgs-doublet models (2HDMs), where there are five Higgs bosons. By confronting the parameter spaces of some 2HDMs with publically available data from the LHC, the prospects for finding the 2HDM Higgs bosons is presented through the calculation of production cross sections and decay branching ratios in various channels.

A new kind of 2HDM, called the Stealth Doublet Model is presented and the properties of the Higgs bosons are studied. In this model, it is shown that in particular the properties of the charged Higgs boson H± have new features not exhibited in earlier studied models. Within the parameter space compatible with the LHC results, the production cross section for H± can be sizeable enough to be experimentally observed.

Finally, the discovery prospects at the LHC, for a H± in the pptH± process, with the decays H±HW± and Hbb, is studied in various models beyond the Standard Model. It is shown that for the supersymmetric models, this channel is beyond the discovery reach of the LHC. In some of the other studied models, in particular the Aligned 2HDM, the situation is improved and the channel is feasible.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2015. , 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1217
Keyword [en]
Particle physics, The Standard Model, Higgs bosons, Higgs mechanism, Beyond the Standard Model, Two Higgs Doublet Models, Charged Higgs boson, Higgs decays, Supersymmetry, Renormalization, LHC, Collider constraints
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-240617ISBN: 978-91-554-9138-3 (print)OAI: oai:DiVA.org:uu-240617DiVA: diva2:776866
Public defence
2015-02-27, Sal Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2015-02-06 Created: 2015-01-08 Last updated: 2015-03-09
List of papers
1. Higgs properties in a broken Inert Doublet Model
Open this publication in new window or tab >>Higgs properties in a broken Inert Doublet Model
2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 8, 079Article in journal (Refereed) Published
Abstract [en]

We consider a model for the Higgs sector with two scalar doublets and a softly broken Z2 symmetry, the Stealth Doublet Model. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken Z2 symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the H→ γγ channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2013
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-201544 (URN)10.1007/JHEP08(2013)079 (DOI)000324113700079 ()
Funder
Swedish Research Council, 2007-4071
Note

Erratum in Journal of High Energy Physics 2015:87, doi:10.1007/JHEP01(2015)087.

Available from: 2013-06-12 Created: 2013-06-12 Last updated: 2017-12-06Bibliographically approved
2. Higgs phenomenology in the Stealth Doublet Model
Open this publication in new window or tab >>Higgs phenomenology in the Stealth Doublet Model
2015 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, 095002Article in journal (Refereed) Published
Abstract [en]

We analyze a model for the Higgs sector with two scalar doublets and a softly broken Z2 symmetry. One of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions. The other doublet has no vacuum expectation value and no tree-level couplings to fermions. Because the Z2 parity is broken the two doublets can mix, which leads to a distinct and novel phenomenology. This Stealth Doublet Model can be seen as a generalization of the Inert Doublet Model with a broken Z2 symmetry. We outline the model and present constraints from theory, electroweak precision tests and collider searches, including the recent observation of a Higgs boson at the LHC. The CP-odd scalar A and the charged scalar H± couple to fermions at one-loop level. We compute the decays of A and H± and in particular the one-loop decays A→ff¯, H±→ff¯′, H±→W±Z and H±→W±γ. We also describe how to calculate and renormalize such processes in our model. We find that if one of H± or A is the lightest scalar, H±→W±γ or A→bb¯ are typically their respective dominating decay channels. Otherwise, the dominating decays of H± and Aare into a scalar and a vector. Due to the absence of tree-level fermion couplings for H± and A, we consider pair production and associated production with vector bosons and scalars at the LHC. If the parameter space of the model that favors H±→W±γ is realized in Nature, we estimate that there should be a considerable amount of such events in the present LHC data.

Keyword
Higgs boson, extended Higgs sector, Large Hadron Collider
National Category
Subatomic Physics
Research subject
Theoretical Physics; Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-211544 (URN)10.1103/PhysRevD.91.095002 (DOI)000353774700002 ()
Funder
Swedish Research Council, 2007-4071Swedish Research Council, 621-2011-5333
Available from: 2013-11-26 Created: 2013-11-26 Last updated: 2017-12-06Bibliographically approved
3. Charged Higgs boson in the W± Higgs channel at the Large Hadron Collider
Open this publication in new window or tab >>Charged Higgs boson in the W± Higgs channel at the Large Hadron Collider
Show others...
2015 (English)In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 893, 420-442 p.Article in journal (Refereed) Published
Abstract [en]

In light of the recent discovery of a neutral Higgs boson, Hobs, with a mass near 125 GeV, we reassess the LHC discovery potential of a charged Higgs boson, H±, in the W±Hobs decay channel. This decay channel can be particularly important for a H± heavier than the top quark, when it is produced through the pp→tH± process. The knowledge of the mass of Hobsprovides an additional handle in the kinematic selection when reconstructing a Breit-Wigner resonance in the Hobs→bb¯ decay channel. We consider some extensions of the Standard Model Higgs sector, with and without supersymmetry, and perform a dedicated signal-to-background analysis to test the scope of this channel for the LHC running at design energy (14 TeV), for 300/fb (standard) and 3000/fb (high) integrated luminosities. We find that, while this channel does not show much promise for a supersymmetric H± state, significant portions of the parameter spaces of several two-Higgs doublet models are testable.

Keyword
Higgs boson, charged Higgs boson, LHC, supersymmetry
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-240312 (URN)10.1016/j.nuclphysb.2015.02.001 (DOI)000352045000019 ()
Funder
Swedish Research Council, 2007-4071Swedish Research Council, 621-2011-5107
Available from: 2015-01-07 Created: 2015-01-07 Last updated: 2017-12-05Bibliographically approved
4. A light second Higgs doublet in light of LHC data
Open this publication in new window or tab >>A light second Higgs doublet in light of LHC data
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We confront the general, CP-conserving, two-Higgs-doublet model (2HDM) with Yukawa couplings of Types I–IV with all the data present from run-I of the LHC. For the allowed regions of parameter space, we investigate to what extent there can still exist relatively light scalars, and under which conditions they may be within discovery reach for upcoming LHC runs.

Keyword
Higgs Bosons, LHC, Beyond the Standard Model, Two Higgs Doublet Models
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-240603 (URN)
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2015-03-09

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