| 1. |
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| 2. |
- Alwall, Johan, et al.
(författare)
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Improved description of charged Higgs boson production at hadron colliders
- 2004
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; 0412:050
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Tidskriftsartikel (refereegranskat)abstract
- We present a new method for matching the two twin-processes gb→H±t and gg→H±tb in Monte Carlo event generators. The matching is done by defining a double-counting term, which is used to generate events that are subtracted from the sum of these two twin-processes. In this way we get a smooth transition between the collinear region of phase space, which is best described by gb→H±t, and the hard region, which requires the use of the gg→H±tb process. The resulting differential distributions show large differences compared to both the gb→H±t and gg→H±tb processes illustrating the necessity to use matching when tagging the accompanying b-jet.
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| 3. |
- Alwall, Johan, 1975-
(författare)
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Quark Distributions and Charged Higgs Boson Production : Studies of Proton Structure and New Physics
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction.In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model.Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -> tH+/- and gg -> tbH+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process.
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| 4. |
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| 5. |
- Alwall, Johan, et al.
(författare)
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The pp -> tbH+/- process at the Tevatron in Herwig and Pythia simulations
- 2004
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Ingår i: The European Physical Journal C: Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 39, s1, s. s37-s39
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Tidskriftsartikel (refereegranskat)abstract
- Charged Higgs boson production in association with a top quark could be the first indication of the existence of Higgs particles. The Tevatron Run-II started data-taking in April 2001 at $\sqrt s=1960$ GeV and could probe the existence of a charged Higgs boson beyond the current mass limit. We study the $\rm p\bar p \rightarrow tbH^\pm$ production process with Monte Carlo simulations in HERWIG and PYTHIA, comparing expected cross sections and basic selection variables.
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| 6. |
- Bijnens, Johan, et al.
(författare)
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Constraining general two Higgs doublet models by the evolution of Yukawa couplings
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :5
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Tidskriftsartikel (refereegranskat)abstract
- We study how general two Higgs doublet models can be constrained by considering their properties under renormalization group evolution of the Yukawa couplings. We take into account both the appearance of a Landau pole as well as off-diagonal Yukawa couplings leading to flavour changing neutral currents in violation with experimental constraints at the electroweak scale. We find that the latter condition can be used to limit the amount of Z(2) symmetry breaking allowed in a given model.
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| 7. |
- Bijnens, Johan, et al.
(författare)
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Constraining general two Higgs doublet models by the evolution of Yukawa couplings
- 2012
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Ingår i: Proceedings of Science.
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Konferensbidrag (refereegranskat)abstract
- We analyse the constraints of the general two Higgs doublet models by evolving the Yukawa coupling constants to high energy under renormalization group. We consider the appearance of a Landau pole or large off-diagonal Yukawa couplings which cause tree level flavour changing neutral currents. Our study shows the latter condition can be used to answer how much Z 2 symmetry breaking can be allowed in a given 2HDM model.
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| 8. |
- Bijnens, Johan, et al.
(författare)
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Scalar kinetic mixing and the renormalization group
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 792, s. 238-243
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Tidskriftsartikel (refereegranskat)abstract
- Quantum field theories containing scalar fields with equal quantum numbers allow for a mixed kinetic term in the Lagrangian. It has been argued that this mixing must be taken into consideration when performing renormalization group (RG) analyses of such a theory. However, from the fact that scalar kinetic mixing does not correspond to a physical observable, we show that no extra parameters need to be introduced. Using a toy model, we explicitly derive the 1-loop RG equations (RGEs) in three different renormalization schemes to demonstrate how this issue can be dealt with. In schemes without kinetic mixing, either the fields mix during renormalization to produce non-diagonal anomalous dimensions or the RGEs explicitly depend on the scalar masses. Finally, we show how the different schemes are related to each other by scale dependent field redefinitions.
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| 9. |
- Armesto, N., et al.
(författare)
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Heavy-ion collisions at the LHC-Last call for predictions
- 2008
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 35:5, s. 054001-
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Forskningsöversikt (refereegranskat)abstract
- This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.
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| 10. |
- Bandyopadhyay, Triparno, et al.
(författare)
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Complementary bound on the W′ mass from Higgs boson to diphoton decays
- 2019
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Ingår i: Physical Review D. - 2470-0010. ; 99:11
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Tidskriftsartikel (refereegranskat)abstract
- Using the left-right symmetric model as an illustrative example, we suggest a simple and straightforward way of constraining the W′ mass directly from the decay of the Higgs boson to two photons. The proposed method is generic and applicable to a diverse range of models with a W′-boson that couples to the Standard Model-like Higgs boson. Our analysis exemplifies how the precision measurement of the Higgs to diphoton signal strength can have a pivotal role in probing the scale of new physics.
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| 11. |
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| 12. |
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| 13. |
- Carloni, Lisa, et al.
(författare)
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Discerning secluded sector gauge structures
- 2011
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- New fundamental particles, charged under new gauge groups and only weakly coupled to the standard sector, could exist at fairly low energy scales. In this article we study a selection of such models, where the secluded group either contains a softly broken U(1) or an unbroken SU(N). In the Abelian case new gamma(v) gauge bosons can be radiated off and decay back into visible particles. In the non-Abelian case there will not only be a cascade in the hidden sector, but also hadronization into new pi(v) and rho(v) mesons that can decay back. This framework is developed to be applicable both for e(+) e(-) and pp collisions, but for these first studies we concentrate on the former process type. For each Abelian and non-Abelian group we study three different scenarios for the communication between the standard sector and the secluded one. We illustrate how to distinguish the various characteristics of the models and especially study to what extent the underlying gauge structure can be determined experimentally.
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| 14. |
- Coniavitis, Elias, 1982-
(författare)
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Charged Higgs Bosons at the ATLAS Experiment and Beyond
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the ATLAS experiment at the Large Hadron Collider (LHC) at CERN, direct searches for the elusive Higgs boson will be conducted, as well as for physics beyond the Standard Model. The charged Higgs boson (H±) is interesting both as a part of the Higgs sector, and as a clear sign of new physics. This thesis focuses on H± searches, with H± production in top-antitop pair events, and in particular the bW± bH±, H±→τhadν, W±→qq channel. Its potential was investigated as part of a larger study of the expected performance of the entire ATLAS experiment. Full simulation of the ATLAS detector and trigger was used, and all dominant systematics considered. It was shown to be the most promising H± discovery channel for mH±t.As hadronic τ decays are important for H± searches, their correct identification is critical. Possibilities of improving tau-jet identification in pile-up and top-antitop pair events were investigated. Redundant or even performance-reducing variables in the default likelihood identification were identified, as were new variables showing discriminatory power. This allows for increased rejection of QCD jets in these environments, and higher robustness of the method.Before any physics studies, a commissioned and well-understood detector is required. The Lorentz angle of the ATLAS Semi-Conductor Tracker (SCT) barrel was measured using 2008 cosmic-ray data. It is an important observable for the performance of several detector aspects. Potential sources of systematics were investigated and evaluated. The Lorentz angle in the SCT barrel was measured as θL = 3.93 ± 0.03(stat) ± 0.10(syst) degrees, agreeing with the model prediction.The Compact Linear Collider (CLIC) is a proposed successor to the LHC. The potential for charged and heavy neutral Higgs bosons at CLIC was investigated, in terms of both discovery and precision measurement of parameters like tanβ or the Higgs masses, up to and beyond 1 TeV, which would be challenging at the LHC
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| 15. |
- Dombey, S., et al.
(författare)
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QCD evolution of jets in the quark-gluon plasma
- 2008
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Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 808, s. 178-191
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Tidskriftsartikel (refereegranskat)abstract
- The quark-gluon plasma (QGP) can be explored in relativistic heavy ion collisions by the jet quenching signature, i.e. by the energy loss of a high energy quark or gluon traversing the plasma. We introduce a novel QCD evolution formalism in the leading logarithm approximation, where normal parton radiation is interleaved with scattering on the plasma gluons occuring at a similar time scale. The idea is elaborated in two approaches. One extends the DGLAP evolution equations for fragmentation functions to include scatterings in the medium, which facilitates numerical solutions for comparison with data and provides a basis for a Monte Carlo implementation. The other approach is more general by including also the transverse momentum dependence of the jet evolution, which allows a separation of the scales also for the scattering term and provides a basis for analytical investigations. The two approaches are shown to be related and give the same characteristic softening of the jet depending on the temperature of the plasma. A substantial effect is found at the RHIC energy and is further enhanced at LHC. Systematic studies of data on the energy loss could, therefore, demonstrate the existence of the QGP and probe its properties.
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| 16. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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LEPTO 6.5 - A Monte Carlo generator for deep inelastic lepton-nucleon scattering
- 1997
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Ingår i: COMPUTER PHYSICS COMMUNICATIONS. - : ELSEVIER SCIENCE BV. - 0010-4655. ; 101:1-2, s. 108-134
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Tidskriftsartikel (refereegranskat)abstract
- Physics and programming aspects are discussed for a Fortran 77 Monte Carlo program to simulate complete events in deep inelastic lepton-nucleon scattering. The parton level interaction is based on the standard model electroweak cross sections, which are f
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| 17. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Quarkonium production at the Fermilab Tevatron through soft color interactions
- 1997
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Ingår i: PHYSICAL REVIEW D. - : AMER INST PHYSICS. - 0556-2821. ; 56:11, s. 7317-7320
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Tidskriftsartikel (refereegranskat)abstract
- The direct charmonium and bottomonium production rate observed at high p(perpendicular to) in p (p) over bar collisions at the Fermilab Tevatron is factors of 10 larger than predictions based on conventional perturbative QCD. We show that this excess can
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| 18. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Rapidity Gaps in DIS through Soft Colour Interactions
- 1995
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Ingår i: In proc. of workshop `DIS and QCD', Paris, April 1995.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a new mechanism for the creation of large rapidity gaps in DIS events at HERA. Soft colour interactions between perturbatively produced partons and colour-charges in the proton remnant, modifies the colour structure for hadronization giving col
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| 19. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Soft Colour Exchanges and the Hadronic Final State
- 1999
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Ingår i: Proc. of workshop Monte Carlo Generators for HERA Physics. ; , s. 280-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The models for soft colour interactions and colour string re-interactions, implemented in the Monte Carlo program LEPTO, are investigated regarding hadronic final states in inclusive and diffractive deep inelastic scattering.
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| 20. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Soft colour interactions and the diffractive structure function
- 1996
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Ingår i: JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS. - : IOP PUBLISHING LTD. ; , s. 943-946
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Konferensbidrag (refereegranskat)abstract
- We discuss our model for soft colour interactions and present results on the diffractive structure function F-2(D)(beta, x(P), Q(2)) and inclusive transverse energy flows, which agree with available HERA data.
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| 21. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Soft colour interactions as the origin of rapidity gaps in DIS
- 1996
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Ingår i: PHYSICS LETTERS B. ; 366:1-4, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- We introduce soft colour interactions as a novel mechanism to understand the observed events with large rapidity gaps in $ep$ collisions at HERA. Colour exchanges between produced partons and colour-charges in the proton remnant modifies the colour struct
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| 22. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
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Unified description of rapidity gaps and energy flows in DIS final states
- 1997
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Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. - : SPRINGER VERLAG. - 0170-9739. ; 75:1, s. 57-70
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Tidskriftsartikel (refereegranskat)abstract
- We show that the 'orthogonal' characteristics of the observed rapidity gaps and large forward energy flows in deep inelastic scattering at HERA, can be described within a single framework. Our Monte Carlo model is based on perturbative QCD matrix elements
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| 23. |
- Edling, Lars, et al.
(författare)
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Celiac disease and giardiasis : a case report
- 2012
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Ingår i: European Journal of Gastroenterology and Hepathology. - : Lippincott Williams & Wilkins. - 0954-691X .- 1473-5687. ; 24:8, s. 984-987
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Tidskriftsartikel (refereegranskat)abstract
- When investigating a patient with suspected celiac disease (CD), several other conditions must be considered, including potential infection with Giardia lamblia. Although giardiasis is rare, its histopathological and serological picture may resemble that of CD. We report the case of a young man with diabetes mellitus and a family history of CD referred to our hospital because of diarrhoea and weight loss. Investigation showed, among other factors, partial villous atrophy in duodenal biopsies and elevated immunoglobulin A antitissue transglutaminase antibodies. The patient was diagnosed with CD and recommended a gluten-free diet. At the same time, faecal tests were conducted, indicating the presence of G. lamblia. The patient was treated and improved, even after discontinuing the gluten-free diet. Subsequent follow-up after 6 months showed total regression of mucosal histopathology and a normal antitissue transglutaminase antibodies level. Eur J Gastroenterol Hepatol 24:984-987 (c) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.
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| 24. |
- Ekstedt, Andreas
(författare)
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Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 25. |
- Enberg, Rikard, et al.
(författare)
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Higgs phenomenology in the Stealth Doublet Model
- 2015
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 91
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Enberg, Rikard, et al.
(författare)
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Higgs properties in a broken Inert Doublet Model
- 2013
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Berlin/Heidelberg. - 1126-6708 .- 1029-8479. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Enberg, Rikard, et al.
(författare)
-
Higgs properties in a softly broken Inert Doublet Model
- 2013
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :8
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a model for the Higgs sector with two scalar doublets and a softly broken Z(2) 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 Z(2) 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 -> gamma gamma 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.
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| 28. |
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| 29. |
- Eriksson, David, et al.
(författare)
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2HDMC - two-Higgs-doublet model calculator
- 2010
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 181:1, s. 189-205
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Tidskriftsartikel (refereegranskat)abstract
- We describe the public C++ code 2HDMC which can be used to perform calculations in a general, CP-conserving, two-Higgs-doublet model (2HDM). The program features simple conversion between different parametrizations of the 2HDM potential, a flexible Yukawa sector specification with choices of different Z_2-symmetries or more general couplings, a decay library including all two-body - and some three-body - decay modes for the Higgs bosons, and the possibility to calculate observables of interest for constraining the 2HDM parameter space, as well as theoretical constraints from positivity and unitarity. The latest version of the 2HDMC code and full documentation is available from: http://www.isv.uu.se/thep/MC/2HDMC.
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| 30. |
- Eriksson, David, et al.
(författare)
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Associated charged Higgs and W boson production in the MSSM at the CERN Large Hadron Collider
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the viability of observing charged Higgs bosons (H^+/-) produced in association with W bosons at the CERN Large Hadron Collider, using the leptonic decay H^+ -> tau^+ nu_tau and hadronic W-decay, within different scenarios of the Minimal Supersymmetric Standard Model (MSSM) with both real and complex parameters. Performing a parton level study we show how the irreducible Standard Model background from W+2 jets can be controlled by applying appropriate cuts and find that the size of a possible signal depends on the cuts needed to suppress QCD backgrounds and misidentifications. In the standard maximal mixing scenario of the MSSM we find a viable signal for large tan(beta) and intermediate H^+/- masses (~m_t) when using optimistic cuts whereas for more pessimistic ones we only find a viable signal for very large tan(beta) (>~50). We have also investigated a special class of MSSM scenarios with large mass-splittings among the heavy Higgs bosons where the cross-section can be resonantly enhanced by factors up to one hundred, with a strong dependence on the CP-violating phases. Even so we find that the signal after cuts remains small except for small masses (~< m_t) with optimistic cuts. Finally, in all the scenarios we have investigated we have only found small CP-asymmetries.
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| 31. |
- Eriksson, David, et al.
(författare)
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Associated charged Higgs and W boson production in the MSSM at the CERN Large Hadron Collider
- 2008
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 53:2, s. 267-280
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the viability of observing charged Higgs bosons () produced in association with bosons at the CERN large hadron collider, using the leptonic decay and hadronic decay, within different scenarios of the minimal supersymmetric standard model (MSSM) with both real and complex parameters. Performing a parton level study we show how the irreducible standard model background from jets can be controlled by applying appropriate cuts and find that the size of a possible signal depends on the cuts needed to suppress QCD backgrounds and misidentifications. In the standard maximal mixing scenario of the MSSM we find a viable signal for large and intermediate masses () when using softer cuts (, 50 GeV), whereas for harder cuts (, 100 GeV) we only find a viable signal for very large (). We have also investigated a special class of MSSM scenarios with large mass splittings among the heavy Higgs bosons where the cross-section can be resonantly enhanced by factors up to one hundred, with a strong dependence on the -violating phases. Even so we find that the signal after cuts remains small except for small masses () when using the softer cuts. Finally, in all the scenarios we have investigated we have only found small -asymmetries.
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| 32. |
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| 33. |
- Eriksson, David, et al.
(författare)
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Color rearrangements in B-meson decays
- 2009
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 79:1, s. 014011-
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Tidskriftsartikel (refereegranskat)abstract
- Wepresent a new model, based on color rearrangements, which atthe same time can describe both hidden and open charmproduction in B-meson decays. The model is successfully compared toboth inclusive decays, such as B-->J/psiX and B-->DsX, as wellas exclusive ones, such as B-->J/psiK(*) and B-->D(*)D(*)K. It alsogives a good description of the momentum distribution of directJ/psi's, especially in the low-momentum region, which earlier has beenclaimed as a possible signal for new exotic states.
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| 34. |
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| 35. |
- Eriksson, David, et al.
(författare)
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New angles on top quark decay to a charged Higgs
- 2009
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; 01:1, s. 024-
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Tidskriftsartikel (refereegranskat)abstract
- To properly discover a charged Higgs Boson (H±) requires its spin and couplings to be determined. We investigate how to utilize t spin correlations to analyze the H± couplings in the decay t → bH+ → bτ+ντ. Within the framework of a general Two-Higgs-Doublet Model, we obtain results on the spin analyzing coefficients for this decay and study in detail its spin phenomenology, focusing on the limits of large and small values for tan β. Using a Monte Carlo approach to simulate full hadron-level events, we evaluate systematically how the H± → τ±ντ decay mode can be used for spin analysis. The most promising observables are obtained from azimuthal angle correlations in the transverse rest frames of t(). This method is particularly useful for determining the coupling structure of H± in the large tan β limit, where differences from the SM are most significant.
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| 36. |
- Eriksson, David, 1977-
(författare)
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Phenomenology of Charged Higgs Bosons and B-meson Decays
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For more than 30 years the Standard Model has been the theoretical foundation for particle physics. The theory has been verified successfully by experimental tests. Its biggest shortcoming is the non-discovery of the Higgs boson,responsible for giving the other particles masses. Despite its success there are hints that the Standard Model is not the complete theory and many extensions of it, such as supersymmetry, have been proposed. Extended theories often predict the existence of a charged Higgs boson and its detection will be a clear sign of physics beyond the Standard Model. The main focus in this thesis is on various phenomenological aspects of the charged Higgs boson. For favorable mass and couplings direct detection is shown to be possible at the Large Hadron Collider in production with an associated W boson. It is also shown how a light charged Higgs can have measurable effects on spin correlations in decays of pair-produced top quarks. The charged Higgs boson can also be seen indirectly, in for example B-meson decays, which can be used to put constraints on its mass and fermion couplings. Exclusion limits in two supersymmetric models are given together with a comparison with the discovery potentials for the LHC experiments. A tool for calculating properties, such as masses and decays, of both charged and neutral Higgs bosons in the Two-Higgs-Doublet Model is also presented. B-meson decays can also be used to test aspects of the strong interaction. Part of this thesis deals with improving and applying phenomenological models to B-meson decays. Although these models are not derived from first principles, their success shows that they capture important features of non-perturbative strong interactions.
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| 37. |
- Gabrielli, Emidio, et al.
(författare)
-
Higgs-boson-plus-photon production at the CERN Large Hadron Collider : A clean probe of the b-quark parton densities
- 2008
-
Ingår i: Physical Review D. Particles and fields. - 0556-2821 .- 1089-4918. ; 77:1, s. 015007-
-
Tidskriftsartikel (refereegranskat)abstract
- Higgs boson production in association with a high p(T) photon at the CERN Large Hadron Collider is analyzed, in the framework of the MSSM model, for the heavier neutral Higgs bosons. The request of an additional photon in the exclusive Higgs boson final state selects b-quark pairs among the possible initial partonic states, since gluon-gluon initial states are not allowed by C-parity conservation. Hence, the measurement of cross sections for neutral Higgs boson plus photon production can provide a clean probe of the b-quark density in the proton as well as of the b-quark Yukawa coupling. The suppression of the production rates by the b-quark electromagnetic coupling can be compensated by the enhanced Higgs boson Yukawa coupling to b's in the large tan beta regime. The Higgs boson decay into a tau-lepton pair is considered, and irreducible backgrounds with corresponding signal significances are evaluated.
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| 38. |
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| 39. |
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| 40. |
- Ingelman, Gunnar, et al.
(författare)
-
Diffractive W-+/- production at hadron colliders as a test of color singlet exchange mechanisms
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 87:9, s. 094017-
-
Tidskriftsartikel (refereegranskat)abstract
- We revisit diffractive and exclusive (WX)-X-+/- production at hadron colliders in different models for soft color exchanges. The process pp -> p[(WX)-X-+/-]p, and in particular a W-+/- charge asymmetry, has been suggested as a way to discriminate diffractive processes as being due to pomeron exchange in Regge phenomenology or QCD-based color reconnection models. Our detailed analysis of the latter models at LHC energies shows, however, that they give similar results as pomeron models for leading protons and central (WX)-X-+/- production, including a vanishing W-+/- charge asymmetry. We demonstrate that soft color exchange models provide a continuous transition from diffractive to inelastic processes and thereby include the intrinsic asymmetry of inelastic interactions while being at the same time sensitive to the underlying hadronization models. Such sensitivity also concerns the differential distributions in proton momentum and W-+/- transverse momentum, which opens possibilities to discriminate between different color reconnection models.
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| 41. |
- Ingelman, Gunnar, et al.
(författare)
-
Rapidity gaps from colour string topologies
- 1999
-
Ingår i: Nuclear physics B, Proceedings supplements. - 0920-5632 .- 1873-3832. ; 79:1-3, s. 386-388
-
Tidskriftsartikel (refereegranskat)abstract
- Diffractive deep inelastic scattering at HERA and diffractive W and jet production at the Tevatron are well described by soft colour exchange models. Their essence is the variation of colour string-field topologies giving both gap and no-gap events, with a smooth transition and thereby a unified description of all final states.
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| 42. |
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| 43. |
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| 44. |
- Karlsson, Niklas
(författare)
-
Parametric model for astrophysical proton-proton interactions
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Observations of gamma-rays have been made from objects such as active galaxies and supernova remnants and also as diffuse emission from the Galactic ridge. The study of gamma-rays can provide information about production mechanisms and tell us about cosmic ray acceleration. In the high energy regime, the dominant mechanism for gamma-ray production is the decay of neutral pions produced in interactions of accelerated cosmic ray nuclei and interstellar matter. Having an accurate model for this is an integral part in the study of gamma-rays and the sources in which they are produced. We present here a parametric model for calculations of inclusive cross sections for stable secondary particles (gamma-rays, electrons, positrons, nue, anti nue, numu and anti numu) produced in proton-proton interactions. The model is based on the up-to-date proton-proton interaction model by Kamae et al., which includes the diffraction dissociation process, violation of the Feynman scaling law and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added to the model: one representing the Δ(1232) and the other multiple resonances with masses around 1600 MeV/c^2. The parametric model predicts the spectra for all secondary particles to be harder by about 0.05 in power-law index than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on Feynman scaling. The transverse momentum distributions for gamma-rays have also been calculated from the described proton-proton interaction model, showing the potential of also having a parametric model for the transverse momentum distributions.
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| 45. |
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| 46. |
- Mahmoudi, F., et al.
(författare)
-
Light Higgs bosons in phenomenological NMSSM
- 2011
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 71:4, s. 1608-
-
Tidskriftsartikel (refereegranskat)abstract
- We consider scenarios in the next-to-minimal supersymmetric model (NMSSM) where the CP-odd and charged Higgs bosons are very light. As we demonstrate, these can be obtained as simple deformations of existing phenomenological MSSM benchmarks scenarios with parameters defined at the weak scale. This offers a direct and meaningful comparison to the MSSM case. Applying a wide set of up-to-date constraints from both high-energy collider and flavor physics, the Higgs boson masses and couplings are studied in viable parts of parameter space. The LHC phenomenology of the light Higgs scenario for neutral and charged Higgs boson searches is discussed.
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| 47. |
- Moretti, M., et al.
(författare)
-
Production of light Higgs pairs in 2-Higgs doublet models via the Higgs-strahlung process at the LHC
- 2010
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :11, s. 097-
-
Tidskriftsartikel (refereegranskat)abstract
- At the Large Hadron Collider, we prove the feasibility to detect pair production of the lightest CP-even Higgs boson h of a Type II 2-Higgs Doublet Model through the process q (q) over bar ((')) -> V hh ( Higgs-strahlung, V = W-+/-, Z), in presence of two h -> b (b) over bar decays. We also show that, through such production and decay channels, one has direct access to the following Higgs self-couplings, thus enabling one to distinguish between a standard and the Supersymmetric version of the above model: lambda(Hhh) - which constrains the form of the Higgs potential - as well as lambda(W +/- H -/+ h) and lambda(ZAh) - which are required by gauge invariance. Unfortunately, such claims cannot be extended to the Minimal Supersymmetric Standard Model, where the extraction of the same signals is impossible.
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| 48. |
- Moretti, M., et al.
(författare)
-
Vector-Boson Production of Light Higgs Pairs in 2-Higgs Doublet Models
- 2007
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- At the Large Hadron Collider, we prove the feasibility to detect pair production of the lightest CP-even Higgs boson h of Type II 2-Higgs Doublet Models through qq(') -> qq(')hh (vector-boson fusion). We also show that, through the hh -> 4b decay channel in presence of heavy-flavour tagging, further exploiting forward/backward jet sampling, one has direct access to the lambda Hhh triple Higgs coupling - which constrains the form of the Higgs potential.
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| 49. |
- Moretti, Stefano, et al.
(författare)
-
Pair production of charged Higgs bosons in association with bottom quark pairs at the Large Hadron Collider
- 2004
-
Ingår i: The European Physical Journal C: Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 33:1, s. 41-52
-
Tidskriftsartikel (refereegranskat)abstract
- We study the process $gg\to b\bar b H^ + H^-$ at large $\tan\beta$ , where it represents the dominant production mode of charged Higgs boson pairs in a Type II 2-Higgs doublet model, including the minimal supersymmetric standard model. The ability to select this signal would in principle enable the measurements of some triple-Higgs couplings, which in turn would help understanding the structure of the extended Higgs sector. We outline a selection procedure that should aid in disentangling the Higgs signal from the main irreducible background. This exploits a signature made up by "four b-quark jets, two light-quark jets, a $\tau$ -lepton and missing energy". While, for $\tan\beta\gtrsim30$ and over a significant $M_{H^\pm}$ range above the top mass, a small signal emerges already at the Large Hadron Collider after 100 fb-1, ten times as much luminosity would be needed to perform accurate measurements of Higgs parameters in the above final state, rendering this channel a primary candidate to benefit from the so-called ldquoSuperrdquo Large Hadron Collider option, for which a tenfold increase in instantaneous luminosity is currently being considered.
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| 50. |
- Oredsson, Joel, et al.
(författare)
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ℤ 2 breaking effects in 2-loop RG evolution of 2HDM
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:2
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the effects of a ℤ 2 symmetry in the CP-conserving Two-Higgs-Doublet-Model (2HDM); which is often imposed to prevent Flavor-Changing-Neutral-Currents (FCNCs) at tree-level. Specifically, we analyze how a breaking of the ℤ 2 symmetry spreads during renormalization group evolution; employing general 2-loop renormalization group equations that we have derived. Evolving the model from the electroweak to the Planck scale, we find that while the case of an exact ℤ 2 symmetric 2HDM is very constrained, a soft breaking of the ℤ 2 symmetry extends the valid parameter space regions. The effects of a hard ℤ 2 breaking in the scalar sector as well as the stability of the flavor alignment ansatz are also investigated. We find that while a hard breaking of the ℤ 2 symmetry in the potential is problematic, since it speeds up the growth of quartic couplings, the generated FCNCs are heavily suppressed. Conversely, we also find that hard ℤ 2 breaking in the Yukawa sector at most gives moderate ℤ 2 breaking in the potential; whereas the FCNCs can become quite sizable far away from the ℤ 2 symmetric regions.
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