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Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Higgs particle was first predicted in 1964, and was discovered in the summer of 2012 at the Large Hadron Collider (LHC). This discovery was the latest in a long list of successful Standard Model predictions spanning the last fifty years. However, some of the Standard Models predictions, such as massless neutrinos, are not in agreement with experiment. Thus, extensions of the Standard Model should be considered. Furthermore, some issues, such as how quarks are bound within the proton, are difficult to study from first principles.

In paper I and II of this thesis, a class of models that contains a new TeV scale neutral vector boson is studied. The parameter space of this class of models is constrained using electroweak precision constraints and 13 TeV LHC data. Gauge anomalies are cancelled both by choosing appropriate fermion charges, and by adding Green-Schwarz terms.

The Higgs mechanism is often studied at leading order, but there are also important radiative corrections. These radiative corrections, which change the ground state energy, can both be IR divergent and gauge dependent. In paper III it is shown how to solve both of these problems. In particular, IR divergences are shown to be spurious.

In paper IV of this thesis, rapidity gaps at the LHC are explained by using a colour singlet two-gluon ladder exchange (BFKL). These exchanges, together with a soft-gluon model, are implemented in a complete Monte Carlo simulation, and reproduce observed rapidity gaps at the LHC.

The momentum distributions of bound partons, quarks and gluons, are described by parton distribution functions (PDFs). In paper V and VI of this thesis, a physically motivated model for PDFs is presented. This model can reproduce proton structure function data, and gives a possible solution to the proton spin puzzle.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 57
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1820
Keywords [en]
QCD, Higgs, Gauge Symmetry, Standard Model, BFKL, PDF, DIS, Beyond the Standard Model, Colliders, Phenomenology, Effective Potential, Anomaly
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics; Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-383273ISBN: 978-91-513-0675-9 (print)OAI: oai:DiVA.org:uu-383273DiVA, id: diva2:1315161
Public defence
2019-08-30, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-06-04 Created: 2019-05-13 Last updated: 2019-06-17
List of papers
1. Constraining minimal anomaly free U(1) extensions of the Standard Model
Open this publication in new window or tab >>Constraining minimal anomaly free U(1) extensions of the Standard Model
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2016 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1611, article id 071Article in journal (Refereed) Published
Abstract [en]

We consider a class of minimal anomaly free U(1) extensions of the Standard Model with three generations of right-handed neutrinos and a complex scalar. Using electroweak precision constraints, new 13 TeV LHC data, and considering theoretical limitations such as perturbativity, we show that it is possible to constrain a wide class of models. By classifying these models with a single parameter, κ, we can put a model independent upper bound on the new U(1) gauge coupling gz. We find that the new dilepton data puts strong bounds on the parameters, especially in the mass region MZ′≲3 TeV.

Keywords
Beyond Standard Model, Gauge Symmetry
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-301819 (URN)10.1007/JHEP11(2016)071 (DOI)000387691500010 ()
Funder
Carl Tryggers foundation , CTS-14:206Swedish Research Council, 621-2011-5107
Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2019-05-13Bibliographically approved
2. Minimal anomalous U(1) theories and collider phenomenology
Open this publication in new window or tab >>Minimal anomalous U(1) theories and collider phenomenology
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2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1802, p. 152-Article in journal (Refereed) Published
Abstract [en]

We study the collider phenomenology of a neutral gauge boson Z′ arising in minimal but anomalous U(1) extensions of the Standard Model (SM). To retain gauge invariance of physical observables, we consider cancellation of gauge anomalies through the Green-Schwarz mechanism. We categorize a wide class of U(1) extensions in terms of the new U(1) charges of the left-handed quarks and leptons and the Higgs doublet. We derive constraints on some benchmark models using electroweak precision constraints and the latest 13 TeV LHC dilepton and dijet resonance search data. We calculate the decay rates of the exotic and rare one-loop Z′ decays to ZZ and Z-photon modes, which are the unique signatures of our framework. If observed, these decays could hint at anomaly cancellation through the Green-Schwarz mechanism. We also discuss the possible observation of such signatures at the LHC and at future ILC colliders.

National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-336639 (URN)10.1007/JHEP02(2018)152 (DOI)000426358100007 ()
Funder
Carl Tryggers foundation , CTS-14:206Swedish Research Council, 621-2011-5107
Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2019-05-13Bibliographically approved
3. On the relationship between gauge dependence and IR divergences in the -expansion of the effective potential
Open this publication in new window or tab >>On the relationship between gauge dependence and IR divergences in the -expansion of the effective potential
2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 226Article in journal (Refereed) Published
Abstract [en]

Perturbative calculations of the effective potential evaluated at a broken minimum, Vmin, are plagued by difficulties. It is hard to get a finite and gauge invariant result for Vmin. In fact, the methods proposed to deal with gauge dependence and ir divergences are orthogonal in their approaches. Gauge dependence is dealt with through the ℏ-expansion, which establishes and maintains a strict loop-order separation of terms. On the other hand, ir divergences seem to require a resummation that mixes the different loop orders. In this paper we test these methods on Fermi gauge Abelian Higgs at two loops. We find that the resummation procedure is not capable of removing all divergences. Surprisingly, the ℏ-expansion seems to be able to deal with both the divergences and the gauge dependence. In order to isolate the physical part of Vmin, we are guided by the separation of scales that motivated the resummation procedure; the key result is that only hard momentum modes contribute to Vmin.

Keywords
Spontaneous Symmetry Breaking, Gauge Symmetry
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-377699 (URN)10.1007/JHEP01(2019)226 (DOI)000457501400005 ()
Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-05-13Bibliographically approved
4. Hard color singlet BFKL exchange and gaps between jets at the LHC
Open this publication in new window or tab >>Hard color singlet BFKL exchange and gaps between jets at the LHC
2017 (English)Report (Other academic)
Abstract [en]

We explore the perturbative QCD dynamics of hard parton-parton scattering through the exchange of a color singlet two-gluon ladder as described by the BFKL equation, resulting in a rapidity gap between two high transverse momentum jets. Implementing this in a complete Monte Carlo event simulation that also accounts for additional QCD processes at softer scales provides dynamical modeling of gap survival probabilities, which makes possible a detailed comparison with data on such jet-gap-jet events. New data from CMS at the LHC extend the dynamic range of the previous Tevatron data, and can be reproduced reasonably well provided that the Soft Color Interaction model is modified based on the idea of reduced resolution power of softer gluon exchanges. This indicates the need for further theoretical developments in connection with other color exchange processes related to rapidity gaps in the hadronic final state.

Keywords
QCD, BFKL, rapidity gaps, jets, Monte Carlo
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-319966 (URN)
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2019-05-13
5. Nucleon parton distributions from hadronic quantum fluctuations
Open this publication in new window or tab >>Nucleon parton distributions from hadronic quantum fluctuations
(English)Manuscript (preprint) (Other academic)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-357641 (URN)
Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2019-09-27
6. Towards solving the proton spin puzzle
Open this publication in new window or tab >>Towards solving the proton spin puzzle
(English)Manuscript (preprint) (Other academic)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-357642 (URN)
Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2019-05-13

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