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Exploring particle physics beyond the Standard Model
Stockholm University, Faculty of Science, Department of Physics.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The standard model of particle physics (SM) is arguably the best tested theory of physics, providing an accurate description of virtually all high energy particle physics phenomena observable in the laboratory. However, the SM also has a number of shortcomings: some of more theoretical nature such as the fine-tuning problem of the Higgs or the strong-CP problem, and some of more phenomenological nature such as not allowing for a satisfying implementation of neutrino masses and the lack of a suitable candidate for the observed dark matter of the Universe.

The SM’s shortcomings have motivated the development of a large number of beyond the SM (BSM) particle physics models. However, no (conclusive) evidence for any BSM model has been found to date. The papers included in this thesis study different approaches to search for BSM physics:

In [I], we studied bounds on weakly interacting massive particle (WIMP) DM models arising from the absence of neutrino signals from DM capture and subsequent DM pair-annihilation in dense astrophysical objects such as the Sun or the Earth. We interpreted these bounds in a model independent fashion, focusing in particular on the scaling of the bounds for the case where WIMPs comprise only a sub-dominant component of the DM. We also used a chemical composition of the Earth updated with respect to the previous literature, strengthening the bound on spin-dependent interactions from capture and annihilation in the Earth by approximately a factor 3.

In [II], we studied the collider phenomenology of one particular BSM model, the next-to-minimal supersymmetric standard model (NMSSM). In particular, we focused on 1) the impact of the presence of the 125 GeV SM-like Higgs boson on the NMSSM parameter space, 2) the identification of NMSSM specific search channels at the LHC which allow to effectively probe the NMSSM parameter space allowed by more conventional searches, and 3) an in-depth study of one of these search channels, the mono-Higgs signature. As shown in [II], this channel allows to probe the low tan β , large m_A regime which is difficult to probe with conventional searches, and in contrast to many conventional Higgs searches, the reach of the mono-Higgs channel improves significantly with the increased luminosity expected to be collected at the LHC in current and future runs.

Place, publisher, year, edition, pages
Stockholm University, 2017.
National Category
Subatomic Physics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-148654OAI: oai:DiVA.org:su-148654DiVA, id: diva2:1154538
Presentation
2017-11-29, FB53, AlbaNova, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Available from: 2018-02-16 Created: 2017-11-02 Last updated: 2018-02-16Bibliographically approved
List of papers
1. Dark matter capture, subdominant WIMPs, and neutrino observatories
Open this publication in new window or tab >>Dark matter capture, subdominant WIMPs, and neutrino observatories
2017 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 4, article id 043007Article in journal (Refereed) Published
Abstract [en]

Weakly interacting massive particles (WIMPs), which are among the best motivated dark matter (DM) candidates, could make up all or only a fraction of the total DM budget. We consider a scenario in which WIMPs are a subdominant DM component; such a scenario would affect both current direct and indirect bounds on the WIMP-nucleon scattering cross section. In this paper we focus on indirect searches for the neutrino flux produced by annihilation of subdominant WIMPs captured by the Sun or the Earth via either spin-dependent or spin-independent scattering. We derive the annihilation rate and the expected neutrino flux at neutrino observatories. In our computation, we include an updated chemical composition of the Earth with respect to the previous literature, leading to an increase of the Earth's capture rate for spin-dependent scattering by a factor of 3. Results are compared with current bounds from Super-Kamiokande and IceCube. We discuss the scaling of bounds from both direct and indirect detection methods with the WIMP abundance.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-142494 (URN)10.1103/PhysRevD.95.043007 (DOI)000394664300001 ()
Available from: 2017-05-12 Created: 2017-05-12 Last updated: 2017-11-29Bibliographically approved
2. NMSSM Higgs boson search strategies at the LHC and the mono-Higgs signature in particular
Open this publication in new window or tab >>NMSSM Higgs boson search strategies at the LHC and the mono-Higgs signature in particular
2017 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 11, article id 115036Article in journal (Refereed) Published
Abstract [en]

We study the collider phenomenology of the extended Higgs sector of the next-to-minimal supersymmetric Standard Model (NMSSM). The region of NMSSM parameter space favored by a 125 GeV SM-like Higgs and naturalness generically features a light Higgs and neutralino spectrum as well as a large O(1) coupling between the Higgs doublets and the NMSSM singlet fields. In such regimes, the heavier Higgs bosons can decay dominantly into lighter Higgs bosons and neutralinos. We study the prospects of observing such decays at the 13 TeV LHC, focusing on mono-Higgs signatures as probes of such regions of parameter space. We present results for the mono-Higgs reach in a framework easily applicable to other models featuring similar decay topologies. In the NMSSM, we find that the mono-Higgs channel can probe TeV scale Higgs bosons and has sensitivity even in the low tan beta, large m(A) regime that is difficult to probe in the MSSM. Unlike for many conventional Higgs searches, the reach of the mono-Higgs channel will improve significantly with the increased luminosity expected to be collected at the LHC in the ongoing and upcoming runs.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-145313 (URN)10.1103/PhysRevD.95.115036 (DOI)000404472700009 ()
Available from: 2017-07-25 Created: 2017-07-25 Last updated: 2017-11-29Bibliographically approved

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