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On the relationship between gauge dependence and IR divergences in the -expansion of the effective potential
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
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.

Place, publisher, year, edition, pages
2019. no 1, article id 226
Keywords [en]
Spontaneous Symmetry Breaking, Gauge Symmetry
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-377699DOI: 10.1007/JHEP01(2019)226ISI: 000457501400005OAI: oai:DiVA.org:uu-377699DiVA, id: diva2:1291473
Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-05-13Bibliographically approved
In thesis
1. Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
Open this publication in new window or tab >>Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
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
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:nbn:se:uu:diva-383273 (URN)978-91-513-0675-9 (ISBN)
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

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Ekstedt, AndreasLöfgren, Johan

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