Publications (79)236.4 Total impact
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ABSTRACT: The motivation for this workshop began with the discovery of the Higgs boson three years ago, and the realisation that many problems remain in particle physics, such as why there is more matter than antimatter, better determining the still poorly measured parameters of the strong force, explaining possible sources for dark matter, naturalness etc. While the newly discovered Higgs boson seems to be compatible with the Standard Model, current experimental accuracy is far from providing a definitive statement with regards to the nature of this new particle. There is a lot of room for physics beyond the Standard Model to emerge in the exploration of the Higgs boson. Recent measurements in highenergy heavy ion collisions at the LHC have shed light on the complex dynamics that govern highdensity quarkgluon interactions. An array of results from the ALICE collaboration have been highlighted in a recent issue of CERN courier. The physics program of highenergy heavy ion collisions promises to further unveil the intricacies of highdensity quarkgluon plasma physics. The great topicality of high energy physics research has also seen a rapid increase in the number of researchers in South Africa pursuing such studies, both experimentally through the ATLAS and ALICE colliders at CERN, and theoretically. Young researchers and graduate students largely populate these research groups, with little experience in presenting their work, and few support structures (to their knowledge) to share experiences with. Whilst many schools and workshops have sought to educate these students on the theories and tools they will need to pursue their research, few have provided them with a platform to present their work. As such, this workshop discussed the various projects being pursued by graduate students and young researchers in South Africa, enabling them to develop networks for future collaboration and discussion. The workshop took place at the iThemba Laboratories  North facility, in Gauteng, from the 11th to the 13th of February 2015, where excellent conference facilities with outdoors and indoor tea areas for discussions and interactions were provided, along with a stateoftheart remote access to the conference venue such that those who were unable to attend the workshop in person could also be present. The laboratory is located next door to the Wits Professional Development Hub (on the corner of Jan Smuts Avenue and Empire Road), which provided the catering for this workshop. A morning plenary session, followed 15+10 minute presentations, was the format across our three days. The topics covered being in highenergy theory and phenomenology (heavy ions, pp, ep, ee collisions), ATLAS physics and ALICE physics. The workshop website is http://hep.wits.ac.za/HEPPW2015.php  [Show abstract] [Hide abstract]
ABSTRACT: A proposed high energy Future Circular HadronElectron Collider would provide sufficient energy in a clean environment to probe diHiggs production. Using this channel we show that the azimuthal angle correlation between the missing transverse energy and the forward jet is a very good probe for the nonstandard $hhh$ and $hhWW$ couplings. We give the exclusion limits on these couplings as a function of integrated luminosity at 95\% C.L. using the fiducial cross sections. The Higgs selfcoupling could be measured to be within factors of $0.84 \, (0.89) < \gonehhh < 1.19 \, (1.12)$ of its expected Standard Model value at $\sqrt{s} = 3.5 \,(5.0)$ TeV for an ultimate 10 $\abinv$ of integrated luminosity.  [Show abstract] [Hide abstract]
ABSTRACT: A brief review on the physics beyond the Standard Model is given, as was presented in the High Energy Particle Physics workshop on the $12^{th}$ of February 2015 at the iThemba North Labs. Particular emphasis is given to the Minimal Supersymmetric Standard Model, with mention of extradimensional theories also.  [Show abstract] [Hide abstract]
ABSTRACT: The nature of spacetime at high energy is an open question and the link between extradimensional theories with the physics of the Standard Model can not be established in a unique way. The compactification path is not unique and supersymmetry breaking can be done in different ways. Compactifications based on hyperbolic orbifolds gather a large number of properties that are useful for this problem, like a Dirac spectrum chiral zero modes, a mass gap with the KaluzaKlein modes, discrete residual symmetries for the stability of dark matter, and interesting cosmological constructions. This shall be explored here for bulk scalar fields, with a roadmap provided for fermionic studies and beyond.  [Show abstract] [Hide abstract]
ABSTRACT: The measurement of the triple Higgs boson coupling is one of the most important goals of the Higgs physics program in present and future collider experiments. This would provide the first direct information on the Higgs potential, which is responsible for electroweak symmetry breaking mechanism. We present a double Higgs production scenario at the Large HadronElectron Collider (LHeC) and Future Circular HadronElectron Collider (FCC he) through e p collisions, which will provide information about trilinear coupling and the possibility of probing new physics, if there is any. The LHeC will provide e  beams to collide headon with proton beams of 7 TeV from the Large Hadron Collider (LHC). The prospect of replacing the LHC with the high energy FCC, with proton beams of 50 TeV, is used for FCChe studies. Energy of the e  is taken to be 60 GeV for both LHeC and FCChe. Effects of nonstandard CPeven and CPodd couplings for hhh, hWW and hhWW have been studied and constrained at a 95% C.L. 
Conference Paper: Twoloop renormalisation in UED models
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ABSTRACT: The evolution equations of the gauge and Yukawa couplings are derived for the twoloop renormalisation group equations in a fivedimensional SM compactified on a $S^1/Z_2$ to yield standard four spacetime dimensions. Different possibilities can be discussed, however, we shall consider the limiting case in which all matter fields are localised on the brane. We will compare our twoloop results to the results found at oneloop level, and investigate the evolution of $\sin^2 \theta_W$ in this scenario also. 
Conference Paper: Large trilinear $A_t$ soft supersymmetry breaking coupling from 5D MSSM
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ABSTRACT: The possibility of generating a large trilinear $A_t$ soft supersymmetry breaking coupling at low energies through renormalisation group evolution in the 5D MSSM is investigated. Using the power law running in five dimensions and a compactification scale in the 10$10^3$ TeV range, to show that gluino mass may drive a large enough $A_t$ to reproduce the measured Higgs mass and have a light stop superpartner below $\sim 1$ TeV as preferred by the fine tuning argument for the Higgs mass.  [Show abstract] [Hide abstract]
ABSTRACT: We attempt a simultaneous fit of the excess in Higgs boson transverse momentum distributions in the $\gamma\gamma$ and $ZZ^*$ decay channels as well as certain excesses in the search for diHiggs boson resonances observed with Run I data at the Large Hadron Collider. An answer is found in a scenario with a heavy scalar with mass in the range $275285$~GeV, together with a scalar dark matter candidate with mass around $5560$~GeV. This is consistent with all cosmological and direct dark matter search constraints, as well as the limit on the invisible decay width of the observed Higgs boson. In this scenario the producion of the heavy scalar in association with single top quark is not suppressed, compared to that of the Higgs boson. It is also important to look out for Higgs boson production in association with intermediate missing transverse energy. Another consequence is the possible decay of the heavy scalar into $VV$, where $V=Z$ and $W^{\pm}$.  [Show abstract] [Hide abstract]
ABSTRACT: We explore unification and natural supersymmetry in a five dimensional extension of the standard model in which the extra dimension may be large, of the order of 110 TeV. Power law running generates a TeV scale A_ term allowing for the observed 125 GeV Higgs and allowing for stop masses below 2 TeV, compatible with a natural SUSY spectrum. We supply the full oneloop RGEs for various models and use metastability to give a prediction that the gluino mass should be lighter than 3.5 TeV for A_t <= 2.5 TeV, for such a compactification scale, with brane localised 3rd generation matter. We discuss why models in which the 1st and 2nd generation of matter fields are located in the bulk are likely to be ruled out. We also look at electroweak symmetry breaking in these models.  [Show abstract] [Hide abstract]
ABSTRACT: The analysis of gravitino fields in curved spacetimes is usually carried out using the NewmanPenrose formalism. In this paper we consider a more direct approach with eigenspinorvectors on spheres, to separate out the angular parts of the fields in a Schwarzschild background. The radial equations of the corresponding gauge invariant variable obtained are shown to be the same as in the NewmanPenrose formalism. These equations are then applied to the evaluation of the quasinormal mode frequencies, as well as the absorption probabilities of the gravitino field scattering in this background. 
Conference Paper: Searching for BSM physics in Higgs to WW coupling with e+e collisions
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ABSTRACT: The study of Higgs production in e + e − collisions presents us with an avenue for studying Higgs to W W coupling in the tchannel. Our understanding of the tensor structure of the Higgs boson is furthered by learning the phenomenology of how it couples to the W W pair in these reactions. This can be done by applying effective coupling strength constants to an effective Lagrangian as beyond standard model (BSM) terms and performing Monte Carlo studies with these terms present. The investigation includes a two dimensional analysis of the polar angle and the Higgs boson momentum, such that the correlation between these variables can lead to enhanced sensitivity to new dynamics. We also present an energy scan of cross sections for the processes. A likelihood analysis is performed to show that an electron positron collider operating with an integrated luminosity of 5fb −1 would be enough to fully realise an admixture of BSM effects. 1. Introduction With the July 2012 discovery of what appears to be the Higgs boson [1, 2], we now have a great opportunity to further our knowledge of the particle. We do know that the particle which was discovered resembles the Higgs boson described by the standard model (SM), but a large amount of research is being conducted with the goal of searching for signatures associated with it which can only be described by physics beyond the standard model (BSM). The Large Hadron Collider (LHC) is the only active provider of data and information pertaining to Higgs production, but we cannot expect it to provide an answer to all of the questions which the scientific community can pose about the Higgs boson. This is why a thorough study of e + e − collisions is vital if we wish to find BSM physics intrinsic to Higgs production. Since e + e − collisions are seldom used to study Higgs production in general, it is necessary to first try and evaluate what BSM effects such a collider can produce. In this study, we do this by computationally modelling the channels in e + e − which are involved in Higgs production, namely the tchannel and schannel, incorporated with BSM parameters. Once the hypotheses are created, a likelihood analysis is used to determine the luminosity which an e + e − collider should have in order to comfortably detect BSM effects experimentally.  [Show abstract] [Hide abstract]
ABSTRACT: The signature produced by the Standard Model Higgs boson in the Vector Boson Fusion (VBF) mechanism is usually pinpointed by requiring two well separated hadronic jets, one of which (at least) of them tends to be in the forward direction. With the increase of instantaneous luminosity at the LHC, the isolation of the Higgs boson produced with the VBF mechanism is rendered more challenging. In this paper the feasibility of single jet tagging is explored in a highluminosity scenario. It is demonstrated that the separation in rapidity between the tagging jet and the Higgs boson can be effectively used to isolate the VBF signal. This variable is robust from the experimental and QCD stand points. Single jet tagging allows us to probe the spinCP quantum numbers of the Higgs boson. 
Conference Paper: Evolution of Quark Masses and Flavour Mixings in the 2UED
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ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are performed for the oneloop renormalisation group equations in sixdimensional models compactified in different possible ways to yield standard four spacetime dimensions. Different possibilities for the matter fields are discussed, that is where they are in the bulk or localised to the brane. These two possibilities give rise to quite similar behaviours when studying the evolution of the Yukawa couplings and mass ratios. We find that for both scenarios, valid up to the unification scale, significant corrections are observed. 
Article: Large $A_{t}$ Without the Desert
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ABSTRACT: Even if the unification and supersymmetry breaking scales are around 106 to 109 TeV, a large A t coupling may be entirely generated at low energies through RGE evolution in the 5D MSSM. Independent of the precise details of supersymmetry breaking, we take advantage of power law running in five dimensions and a compactification scale in the 10 − 103 TeV range to show how the gluino mass may drive a large enough A t to achieve the required 125.5 GeV Higgs mass. This also allows for subTeV stops, possibly observable at the LHC, and preserving GUT unification, thereby resulting in improved naturalness properties with respect to the four dimensional MSSM. The results apply also to models of “split families” in which the first and second generation matter fields are in the bulk and the third is on the boundary, which may assist in the generation of light stops whilst satisfying collider constraints on the first two generations of squarks. 
Article: Large $A_{t}$ Without the Desert
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ABSTRACT: Even if the unification and supersymmetry breaking scales are around $10^6$ to $10^{9}$ TeV, a large $A_t$ coupling may be entirely generated at low energies through RGE evolution in the 5D MSSM. Independent of the precise details of supersymmetry breaking, we take advantage of power law running in five dimensions and a compactification scale in the $1010^3$ TeV range to show how the gluino mass may drive a large enough $A_t$ to achieve the required $125.5$ GeV Higgs mass. This also allows for subTeV stops, possibly observable at the LHC, and preserving GUT unification, thereby resulting in improved naturalness properties with respect to the four dimensional MSSM. The results apply also to models of "split families" in which the first and second generation matter fields are in the bulk and the third is on the boundary, which may assist in the generation of light stops whilst satisfying collider constraints on the first two generations of squarks.  [Show abstract] [Hide abstract]
ABSTRACT: Two compact universal extra dimensional models are an interesting class of models for different theoretical and phenomenological issues, such as the justification of having three standard model fermion families, suppression of proton decay rate, dark matter parity from relics of the 6dimensional Lorentz symmetry, origin of masses and mixings in the standard model. However, these theories are merely effective ones, with typically a reduced range of validity in their energy scale. We explore two limiting cases of the three standard model generations all propagating in the bulk or all localised to a brane, from the point of view of renormalisation group equation evolutions for the Higgs sector and for the neutrino sector of these models. The recent experimental results of the Higgs boson from the LHC allow, in some scenarios, stronger constraints on the cutoff scale to be placed, from the requirement of the stability of the Higgs potential.  [Show abstract] [Hide abstract]
ABSTRACT: Probing signatures of anomalous interactions of the Higgs boson with pairs of weak vector bosons is an important goal of an e + e − collider commissioned as a Higgs factory. We perform a detailed analysis of such potential of a collider operating at 250 − 300 GeV. Mostly using higher dimensional operators in a gaugeinvariant framework, we show that substantial information on anomalous couplings can be extracted from the total rates of sand tchannel Higgs production. The most obvious kinematic distributions, based on angular dependence of matrix elements, are relatively less sensitive with moderate coefficients of anomalous couplings, unless one goes to higher centreofmass energies. Some important quantities to use here, apart from the total event rates, are the ratios of event rates at different energies, ratios of sand tchannel rates at fixed energies, and under some fortunate circumstances, the correlated changes in the rates for Wboson pairproduction. A general scheme of calculating rates with as many as four gaugeinvariant operators is also outlined. At the end, we perform a likelihood analysis using phenomenological parametrization of anomalous HWW interaction, and indicate their distinguishability for illustrative values of the strength of such interactions. 
Article: Evolution of Yukawa couplings and quark flavor mixings in two universal extra dimension models
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ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are derived for the oneloop renormalization group equations in sixdimensional models, compactified in different possible ways to yield standard four spacetime dimensions. Different possibilities for the matter fields are also discussed, such as the case of bulk propagating or brane localized fields. We discuss in both cases the evolution of the Yukawa couplings, the Jarlskog parameter and the CabibboKobayashiMaskawa matrix element, and find that for both scenarios, as we run up to the unification scale, significant renormalization group corrections are present. We also discuss the results of different observables of the fivedimensional universal extra dimension model in comparison with these sixdimensional models and the model dependence of the results. 
Conference Paper: Evolution of Yukawa Couplings and Quark Flavour Mixings in the 5D MSSM
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ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are derived for the oneloop renormalization group equations in the 5D Minimal Supersymmetric Standard Model on an {$S^1 / Z_2$} orbifold. Different possibilities for the matter fields are discussed such as the cases of bulk propagating or brane localised fields. We discuss in both cases the evolution of the mass ratios and the implications for the mixing angles. 
Publication Stats
685  Citations  
236.40  Total Impact Points  
Top Journals
Institutions

20092015

University of the Witwatersrand
 School of Physics
Johannesburg, Gauteng, South Africa


20052012

Kyoto University
 Yukawa Institute for Theoretical Physics
Kioto, Kyōto, Japan


20032011

Korea Institute for Advanced Study
Sŏul, Seoul, South Korea


20072008

Institut de Physique Nucléaire de Lyon
Lyons, RhôneAlpes, France 
Claude Bernard University Lyon 1
 Institut de physique nucléaire de Lyon (IPNL)
Villeurbanne, RhoneAlpes, France


20002008

University of Melbourne
 School of Physics
Melbourne, Victoria, Australia
