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1
El, Faham Hesham. "Phenomenological Studies on Composite Higgs Models." Thesis, Uppsala universitet, Högenergifysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-359903.
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Composite Higgs Models (CHMs) are formulated in terms of strongly coupled theories. They often predict fermionic top partners with a mass around the TeV scale. Going beyond minimality enriches the spectrum of the theory with additional hypothetical scalars that significantly change the phenomenology. In this thesis, we explore an SO(6)/SO(5) CHM with an additional pseudo-scalar custodial singlet. The latter has anomalous couplings to the Standard Model vector bosons. We study the phenomenology of the singlet, including bounds from the available ATLAS and CMS searches in the relevant channels with di-boson and fermionic final states. We used HiggsBounds tool to test the model theoretical predictions against the current exclusion limits. The study is performed at the 8 and 13 TeV experiments at the LHC. We present a model parameter space from which the bounds on the (most sensitive) signal cross sections of the hypothetical singlet can be easily extracted.
2
Safari, Mahmoud. "Composite Higgs models and extra dimensions." Doctoral thesis, SISSA, 2012. http://hdl.handle.net/20.500.11767/4694.
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This thesis is organized as follows. Chapter 2 gives an introduction to the subject starting with a discussion of composite Higgs models where the Higgs arises as a PGB. This is followed by introducing the Minimal Composite Higgs Model (MCHM) as a promising example. A simple fact regarding deconstructed models is then addressed as a link to theories with an extra dimension. Chapter 3 is devoted to certain 5D theories and their holographic interpretation. In the first part of this chapter the holographic method for gauge fields is discussed. This method is then applied to the gauge sector of the minimal composite Higgs model in 5D flat space with boundary kinetic terms. A comparison with the more standard KK approach is made afterwards. Introduction to the notion of
holography for fermions will be the final part if this chapter. In chapter 4 we introduce three composite-Higgs/GHU models in flat space and study in detail their compatibility with EWPT. The gauge sector of these models is that of the MCHM described previously, and they differ in the way the SM fermions are embedded in complete multiplets of the bulk gauge group. In the first model, known as MCHM_5, fermions are embedded in four fundamental representations. In the second model fermions are embedded in two fundamentals, while in the third model they are embedded in one adjoint representation. Fermionic kinetic terms are also introduced on the UV boundary in the last two models. Details of the computation of the 1-loop corrections to the Z ̄bLbL vertex are collected in Appendix A. In Appendix B after a short introduction to EWPT, 1-loop computation of electroweak precision observables as well as the χ^2 fit performed for our three models are explained in detail.
3
Grant, Jackie. "Sphalerons in two Higgs doublet electroweak models." Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341066.
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Tesi, Andrea. "A natural Higgs boson: models and phenomenology." Doctoral thesis, Scuola Normale Superiore, 2014. http://hdl.handle.net/11384/85879.
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After a brief description of the Standard Model of Particle Physics, we introduce the Hierarchy
Problem and its possible resolutions. Among several possibilities we choose two
protection mechanisms that realize a Natural Fermi scale: Composite Higgs and Supersymmetry.
Our aim is to consider realistic natural models for the Fermi scale and compare them
with the experimental data coming (mainly) from precision measurements.
In the case of Composite Higgs, we discuss the ne tuning needed to realize a successful
electro-weak symmetry breaking and accommodate a 125 GeV Higgs. Composite Higgs can
naturally explain such light mass if new coloured fermions with the same quantum numbers
of the top are below or at 1000 GeV. Direct searches are starting to probe the natural region
of this kind of models. However, there are strong constraints on this picture coming from
electro-weak and
avour tests. Although non trivially, it is possible to satisfy the bounds if
appropriate representations of the composite fermions are chosen and an approximate U(2)3 flavour symmetry is at work.
The Minimal Supersymmetric Standard Model (MSSM) experiences a significant finetuning
because a 125 GeV Higgs boson is too heavy to be obtained naturally. After a brief
review of the MSSM and a discussion of its Higgs sector, we consider the Next-to-Minimal
Supersymmetric Standard Model (NMSSM). The NMSSM provides a 125 GeV Higgs boson
with milder tuning and it also mitigates naturalness upper bounds on stops and gluinos,
which start to be strongly constrained from below by direct searches. Another relevant
aspect of the NMSSM is the suggestion that the lightest new particles could be the CP-even
scalars of its extended Higgs sector. This possibility can be efficiently constrained from the
measurements of the Higgs mass and branching ratios at LHC. In many cases the Higgs fit is an important constraint, competitive with direct searches. When these constraints are
absent we outline possible strategies for future experimental searches.
We conclude with a brief summary and comment on the relative importance of electroweak
and Higgs precision measurements in the models discussed in the thesis.
5
Munir, Shoaib. "The Higgs sector of non-minimal supersymmetric models." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439369.
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MELO, MARCUS VINÍCIUS MARINHO PEREIRA DE. "STABILITY AND PERTURBATIVITY CONSTRAINTS ON HIGGS PORTAL MODELS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36052@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O Modelo Padrão é uma das teorias mais bem sucedidas da física de partículas. Com a descoberta do bóson de Higgs, além de ter sido uma demonstração robusta do poder preditivo do Modelo Padrão, foi aberto um novo caminho para a investigação de nova física interagindo por meio do portal de Higgs, incluindo cenários motivados por matéria escura e bariogênese. Investigamos a estabilidade do potencial e os pólos de Landau do Modelo Padrão sob efeito da interação entre o bóson de Higgs e uma partícula escalar. Focamos no regime onde os escalares são gerados primariamente via um off-shell Higgs. Prevemos o espaço de parâmetros disponível para acessar a teoria em diferentes valores de massa do campo escalar.
The Standard Model is one of the most successful theories in particle physics. With the discovery of the Higgs boson, a new pathway has been opened to investigate possible new physics interacting through the Higgs portal, including scenarios motivated by dark matter and baryogenesis. Supposing there is a neutral scalar state in the Standard Model coupled to it only through the Higgs portal, we investigate the potential stability and the Landau poles of the extended Standard Model potential. We focus on the regime in which the scalars are primarily generated via an off-shell Higgs. We predict the available parameter space to probe the theory for different mass values.
7
Yildirim, Emine. "Phenomenological aspects of elementary and composite Higgs models." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/415721/.
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This thesis presents the phenomenological analysis of the charged Higgs sector in 3-Higgs Doublet Models (3HDMs) and that of heavy Higgs bosons in Composite 2-Higgs Doublet Models (C2HDMs). In the first chapter, the main properties of five types of 3HDMs are summarised. In addition, the constraints from the measurements of the B > Xsy decay rate on the parameter space of 3HDMs are considered at the next-to-leading order in QCD and then limits from direct searches for H 1 and H2 at colliders are discussed. In the other chapters, we move on to the investigation of a C2HDM framework based on the spontaneous breakdown of a global symmetry SO(6) → SO(4) × SO(2) at the compositeness scale f. The motivations and the main properties of it are summarised. By requiring C2HDMs to full perturbative unitarity at energies, we obtain constraints on its parameters. We also study the Large Hadron Collider (LHC) phenomenology of C2HDMs of various Yukawa types by concentrating on the modications from Standard Model (SM) couplings of the discovered Higgs state (h) in addition to the production cross sections and Branching Ratios (BRs) of additional Higgs bosons. We find that, even if the same deviation in the hV V (V = W±Z) coupling is established in both a C2HDM and Elementary 2-Higgs Doublet Model (E2HDM), one can disentangle the two scenarios due to the structure of the Yukawa couplings by using the production and decay properties of additional Higgs bosons. Finally, we study single- and double-h production at future e+e− colliders in C2HDMs and E2HDMs. In particular, we study the differences in the cross sections between the two hypotheses when the deviation in the hV V (V = W±Z) coupling is set to be the same value in both scenarios.
8
Seniuch, Michael. "Analysis of the phase structure in extended Higgs models." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980777909.
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Thompson, David Ian. "Low energy consequences of some non-standard Higgs models." Connect to e-thesis, 2007. http://theses.gla.ac.uk/143/.
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Thesis (Ph.D.) - University of Glasgow, 2007.Ph.D. thesis submitted to the Department of Physics and Astronomy, Faculty of Physical Sciences, University of Glasgow, 2007. Includes bibliographical references. Print version also available.
10
Thompson, David I. "Low energy consequences of some non-standard Higgs models." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/143/.
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Little Higgs models offer an innovative solution of the naturalness problem of the Standard Model. These models contain new particles which cancel the quadratic divergences in the Higgs mass caused by the top, gauge and Higgs loops. These new particles contribute to loop induced interactions of the Higgs boson. The loop induced decays of the Higgs to gluon and photon pairs are examined in two Little Higgs models - the Littlest Higgs Model and the Schmaltz Model. The production of Higgs pairs from gluon fusion, which proceeds via heavy quark loops, is also examined in these models. Another idea considered is the multiple point principle (MPP) applied to the two Higgs doublet extension of the Standard Model. The MPP stipulates that the coupling constants will be tuned to allow the existence of a maximal number of degenerate vacua. This principle is shown to lead to a Peccei-Quinn type symmetry which naturally suppresses phenomenologically dangerous flavour changing neutral currents. Quasi-fixed points of the renormalization group are then used to derive predictions for the Higgs masses and couplings.
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Lebedev, Oleg. "Spontaneous CP-Violation in Two Higgs Doublet Supersymmetric Models." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30640.
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An alternative approach to the problem of CP-violation
is presented. It is based on the possibility of
spontaneous CP-breakdown in models with two Higgs doublets.
General features of the phenomenon such as stability of the
vacuum and the existence of a light axion are discussed.
We investigate the feasibility of spontaneously broken
CP in the minimal supersymmetric models - the MSSM and
NMSSM. The latter is shown to be experimentally viable.
The phenomenological implications of the model such as
CP-violating effects in the kaon systems and a nonzero
neutron electric dipole moment are studied.Ph. D.
12
Bazzocchi, Federica. "The Little-Higgs Mechanism in Electroweak and Flavor Physics." Doctoral thesis, SISSA, 2005. http://hdl.handle.net/20.500.11767/4196.
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Krenke, Christopher A. "Aspects of the Theory and Phenomenology of Twin Higgs Models." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193723.
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We begin by reviewing the basic theory and phenomenology of twin Higgs models. In these theories, the Higgs arises as a pseudo-Nambu-Goldstone boson of a spontaneously broken global symmetry. A discrete symmetry restricts the form of the radiatively generated Higgs potential such that dimensionful terms respect this global symmetry. The Higgs mass is then protected from receiving quadratically divergent contributions, allowing natural electroweak symmetry breaking up to a cutoff scale of about 10 TeV. We then show how to incorporate a tree level quartic into the left-right twin Higgs. The addition of such a term results in a substantial reduction in the fine tuning compared to that of the original twin Higgs. We do this by extending the symmetry of the theory to include two Z₂ symmetries, each of which is sufficient to protect Higgs mass from receiving quadratically divergent corrections. Although both parities are broken explicitly, the symmetries that the protect Higgs mass from getting a quadratically divergent mass are broken only collectively. Therefore, the Higgs mass parameter is free from quadratic divergences to one loop. Finally, we consider the collider signatures of the left-right twin Higgs in the limit that the right-handed neutrino mass is less than the right-handed gauge boson mass. In this limit, which has not been considered previously, new leptonic decay channels open up. This allows the discovery of the right-handed gauge boson WR and the heavy top partner T(H), which are responsible for canceling the one-loop quadratic divergences of the Higgs mass. Half of these events contain same-sign leptons without missing energy, which have no SM background. These signals may be used to complement other collider searches, and in certain regions of parameter space, may be the only way to observe the particles responsible for natural electroweak symmetry breaking in the left-right twin Higgs.
14
Nesti, Fabrizio. "Aspects of Large N Analysis for the Yang-Mills-Higgs Model and Matrix Models." Doctoral thesis, SISSA, 1996. http://hdl.handle.net/20.500.11767/4513.
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The first part of this work deals with some new large N ideas for the YMH
model in three dimensions. Needless to say there is a large historical and scientific
background and it is of course difficult to say something really new on these subjects.
Nevertheless some latest ideas on matrix models, subject on which I have worked
in the first part of my period here at SISSA, are a valuable tool and should find
applications in otherwise 'slow' fields. The study of large N model of monopole
gas are not investigated, to our knowledge, for example. This work wants to be a
starting point for this investigation.
Along this analysis we have found many and different problems to think about,
the principal is the reason how the Eguchi Kawai works, an issue that also has not
been completely clarified, despite of the volume of numerical calculations.
After one finds a reliable method for the functional determinant, it will be possible
to draw definite conclusions on the large N monopole gas, which seems promising
some interesting feature, due to the competition of factors which takes place in the
large N limit.
15
Wouda, Glenn. "Phenomenology of Higgs Bosons Beyond the Standard Model." Doctoral thesis, Uppsala universitet, Högenergifysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-240617.
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After a long history of searches, a Higgs boson H was discovered by the ATLAS and the CMS experiments at the Large Hadron Collider (LHC) in 2012. Its properties fit well the ones predicted by the Standard Model (SM) of particle physics. However, the SM can not explain other established properties of Nature, such as the existence of Dark Matter. For this reason, models beyond the SM should be considered. Such models often predict the existence of several Higgs bosons and this thesis explores some of those models. In particular, the possibility to discover a charged Higgs boson, which would be a clear sign of physics beyond the SM, is studied. A commonly studied extension of the SM is the framework of two-Higgs-doublet models (2HDMs), where there are five Higgs bosons. By confronting the parameter spaces of some 2HDMs with publically available data from the LHC, the prospects for finding the 2HDM Higgs bosons is presented through the calculation of production cross sections and decay branching ratios in various channels. A new kind of 2HDM, called the Stealth Doublet Model is presented and the properties of the Higgs bosons are studied. In this model, it is shown that in particular the properties of the charged Higgs boson H± have new features not exhibited in earlier studied models. Within the parameter space compatible with the LHC results, the production cross section for H± can be sizeable enough to be experimentally observed. Finally, the discovery prospects at the LHC, for a H± in the pp → tH± process, with the decays H± → HW± and H → bb, is studied in various models beyond the Standard Model. It is shown that for the supersymmetric models, this channel is beyond the discovery reach of the LHC. In some of the other studied models, in particular the Aligned 2HDM, the situation is improved and the channel is feasible.
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Bélusca, Hermès. "Recherche de nouvelle physique au LHC à partir d'une théorie des champs effective pour le boson de Higgs." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS032/document.
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La découverte au LHC d'un boson scalaire possédant des propriétés fortement similaires à celles du boson de Higgs du Modèle Standard, indique certainement que l'acteur principal du mécanisme de la brisure de symétrie électrofaible a été trouvé. Cependant, plusieurs théories au-delà du Modèle Standard prédisent l'existence d'une particule similaire provenant d'un secteur plus riche. La mesure des propriétés du boson scalaire découvert nous permettra de savoir si celui-ci correspond ou non à la particule prédite par le Modèle Standard. Pour ce faire, nous utilisons une approche modèle-indépendante via le cadre d'une théorie des champs effective (TCE) pour le boson de Higgs, afin de paramétrer les déviations de ses couplages à la matière par rapport au Modèle Standard. Nous nous focalisons sur une théorie basée sur un Lagrangien effectif de dimension 6, qui inclut à la fois des opérateurs de Charge-Parité paire et impaire. Dans un premier temps nous tentons d'obtenir des contraintes sur une partie des coefficients effectifs de Wilson, pertinents pour la physique du boson de Higgs au LHC, en utilisant les dernières données de taux du Higgs provenant du Run-I des expériences ATLAS et CMS, ainsi que des données de précision électrofaibles du LEP, SLC et du Tevatron. Nous montrons que les données actuelles sont capables de contraindre de manière significative les opérateurs de CP paire ainsi que certains opérateurs de CP impaire du Lagrangien effectif. Dans un second temps nous étudions de possibles désintégrations exotiques du boson de Higgs, qui ne sont générées qu'en tant que conséquence des opérateurs effectifs de dimension 6 (générés par de la nouvelle physique inconnue) et non par le Modèle Standard seul. Les limites expérimentales actuelles nous permettent de placer des bornes supérieures sur ces opérateurs. Pour finir nous analysons certaines limitations de l'approche effective, par la comparaison de certains processus avec boson de Higgs à l'ordre des arbres dans la TCE, avec les prédictions pour les mêmes processus calculés à l'arbre et à une boucle, dans une classe simple d'extensions du Modèle Standard connue sous le nom de "Two-Higgs doublet models"The discovery at the LHC of a scalar boson, the properties of which are strongly similar to the ones of the Standard Model Higgs boson, certainly indicate that the main actor of the electroweak symmetry breaking mechanism was found. However, many beyond-the-Standard Model theories predict the existence of such a similar particle coming from a richer sector. Measuring the properties of the discovered scalar will tell us whether or not it is the same particle as the one predicted by the Standard Model. To this aim we use a model-independent approach through a Higgs Effective Field Theory (EFT) framework to parametrize the deviations of its couplings to matter from the Standard Model. We focus on a Higgs EFT framework based on a dimension-6 effective Lagrangian, including both CP-even and CP-odd operators. We first attempt at putting constraints on a part of the effective Wilson coefficients relevant for Higgs physics at the LHC, using the latest Higgs rates data from the Run-I of the ATLAS and CMS experiments, as well as electroweak precision data from LEP, SLC and Tevatron. We show that the current data is able to significantly constrain CP-even and some CP-odd operators of the effective Lagrangian. We then move on to the study of possible exotic Higgs decays, that can only be generated as a consequence of the effective dimension-6 operators (generated from unknown new physics) and not from within the Standard Model alone, and derive upper bounds on those operators given the present experimental limits. Finally we analyze some of the limitations of the effective approach by comparing predictions on some Higgs processes at tree-level in EFT with respect to predictions at tree and 1-loop level on the same processes computed in a simple class of Standard Model extensions known as "Two-Higgs doublet models"
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Ferreira, Júnior José Geilson. "O Bóson de Higgs no contexto do modelo 331 supersimétrico reduzido." Universidade Federal da Paraíba, 2016. http://tede.biblioteca.ufpb.br:8080/handle/tede/9523.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work we built a supersymmetric version of the recently proposed reduced minimal 3-3-1 model using the superfield formalism. We study the mass spectrum of all particles emphasizing on the mass spectrum of the lightest scalars of the model. We show that Higgs mass of 125 GeV requires substantial radiative corrections. To do this, stops do not need develop a large mixing and must have mass around TeV. Moreover, some soft SUSY breaking terms may lie at the electroweak scale, which alleviates some tension concerning fine tuning of the related parameters. The lightest doubly charged scalar may have mass around few hundreds of GeV, which can be probed at the LHC, while the remaining scalars of the model have masses at TeV scale.
A presente tese busca construir a versão supersimétrica do modelo 3-3-1 mínimo reduzido, proposto recentemente, utilizando o formalismo de supercampos. Desenvolvemos o espectro de massa de todas as partículas, dando ênfase ao espectro de massa dos escalares mais leves do modelo. Mostramos que uma massa de 125 GeV para o bóson de Higgs requer correções radiativas substanciais. Para tal, os superparceiros do quark top não necessitam desenvolver uma grande mistura e devem ter massa em torno dos TeV. Além disso, alguns termos de quebra soft de supersimetria podem estar na escala eletrofraca, o que alivia um pouco o ajuste fino destes parâmetros. O mais leve escalar duplamente carregado pode ter massa em torno de algumas centenas de GeV, podendo ser sondado no LHC, enquanto os escalares restantes do modelo têm massas em escala TeV.
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Bertuzzo, Enrico. "Supersymmetric Models with a hierarchical squark spectrum and a heavy Higgs boson." Doctoral thesis, Scuola Normale Superiore, 2011. http://hdl.handle.net/11384/85851.
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Low energy Supersymmetry is one of the best motivated extensions of the
Standard Model of Particle Physics. Here we focus on a particular supersymmetric
framework, taking the masses of the squarks of the rest two generations much
larger than the others and a Higgs boson mass in the (200 ÷ 300) GeV range.
The motivation is twofold: on the one hand a high mass scale for the squarks
of the rest two generations allows at least to soften the Supersymmetric Flavour
problem; on the other hand, a higher Higgs boson mass allows to explain the
lack of signals in the Higgs sector. In Chapter 1 we summarise the main features
of supersymmetric models at the Fermi scale and we identify the problems that
shall be the subject of this thesis. In Chapter 2 we will consider the "Higgs boson
mass problem" and the "Supersymmetric Flavour problem" as related naturalness
problems. In Chapter 3 some phenomenological aspects of supersymmetric
theories with such a "non standard" sparticle spectrum will be studied, namely
gluino decays, production and decay rates of the lightest Higgs boson and some
aspects relevant for the Dark Matter direct detection. At last, in Chapter 4,
we will turn our attention to
flavour signals, implementing an eff ective Minimal
Flavour Violation in the case of a hierarchical squark spectrum and deriving lower
bounds on the masses of the heavy squarks that allow to have agreement with
experiments. The overall conclusions are summarised in Chapter 5.
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Köhlmann, Simon [Verfasser]. "Search for Higgs bosons in Two-Higgs-Doublet models in the h/H → WW(*) → evµv channel with the ATLAS detector / Simon Köhlmann." Wuppertal : Universitätsbibliothek Wuppertal, 2014. http://d-nb.info/1053770375/34.
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Sobolev, Ivan [Verfasser], and Georg [Akademischer Betreuer] Weiglein. "Precise predictions for Higgs physics in supersymmetric models / Ivan Sobolev ; Betreuer: Georg Weiglein." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1216629412/34.
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Carvalho, Dorsch Gláuber. "The electroweak phase transition in two-Higgs-doublet models and implications for LHC searches." Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/60614/.
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Da, Silva Caroline Dos Santos. "Cosmic strings and scalar tensor gravity." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4577/.
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This thesis is concerned with the study of cosmic strings. We studied the values for the Higgs mass and string coupling for which the gravitational effect of an infinite cosmic string in the context of the Einstein theory is not only locally but also globally weak. We conclude this happens for strings formed at scales less or equal to the Planck one with Higgs mass being less or equal to the boson vectorial mass. Then we examined the metric of an isolated self-gravitating abelian-Higgs vortex in dilatonic gravity for arbitrary coupling of the vortex fields to the dilaton. We looked for solutions in both massless and massive dilaton gravity. We compared our results to existing metrics for strings in Einstein and .Jordan-Brans-Dicke theories. We explored the generalisation of Bogomolnyi arguments for our vortices and commented on the effects on test particles. We then included the presence of an axion field and examined the metric of an isolated self-gravitating axionic-dilatonic string. Finally we studied dilatonic strings through black hole solutions in string theory. We concluded that the horizon of non-extreme charged black holes supports the long-range fields of the Nielsen-Olesen string that can be considered as black hole hair and whose gravitational effect is in general the production of a conical deficit into the metric of the black hole background. We also concluded that the effect of the dilaton on the horizon of these black holes is to generate an additional charge.
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Béjar, Latonda Santiago. "Flavor changing neutral decay effects in models with two Higgs boson doublets: Applications to LHC Physics." Doctoral thesis, Universitat Autònoma de Barcelona, 2006. http://hdl.handle.net/10803/3375.
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Pobbe, Federico. "Hiking the ALPs: Signatures and Models." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3425784.
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In this thesis work some aspects of the Axion-Like Particles (ALP) physics are presented. After a didascalic introduction on QCD axions and, more generally, on ALPs, an innovative approach to search for such type of particles at B-factories is explained. In the second part of the work, a solution for an ALP or axion to rise in a composite Higgs model framework is described, including some phenomenological results.
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Pyarelal, Adarsh, and Adarsh Pyarelal. "Hidden Higgses and Dark Matter at Current and Future Colliders." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/624536.
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Despite its indisputable successes, the Standard Model of particle physics (SM) is widely considered to be an effective low-energy approximation to an underlying theory that describes physics at higher energy scales. While there are many candidates for such a theory, nearly all of them predict the existence of additional particles beyond those of the Standard Model. In this work, we present three analyses aimed at discovering new particles at current and future particle colliders.
The first two analyses are designed to probe extended scalar sectors, which often arise in theories beyond the Standard Model (BSM). The structure of these extended scalar sectors can be described by a physically well-motivated class of models, known collectively as Two- Higgs Doublet Models (2HDMs). The scalar mass spectrum of 2HDMs is comprised of two CP-even states h and H, a CP-odd state A, and a pair of charged states H± . Traditional searches for these states at particle colliders focus on finding them via their decays to SM particles. However, there are compelling scenarios in which these heavy scalars decay through exotic modes to non-SM final states. In certain regions of parameter space, these exotic modes can even dominate the conven- tional decay modes to SM final states, and thus provide a complementary avenue for discovering new Higgs bosons.
The first analysis presented aims to discover charged Higgs bosons H± via top decay at the LHC. We find that the exotic decay modes outperform the conventional decay modes for regions of parameter space with low values of the 2HDM parameter tan β.
The second analysis aims to systematically cover all the exotic decay scenarios that are consistent with theoretical and experimental con- straints, at both the 14 TeV LHC and a future 100 TeV hadron collider. We find that the preliminary results are promising - we are able to ex- clude a large swathe of 2HDM parameter space, up to scalar masses of 3.5 TeV, for a wide range of values of tan β, at a 100 TeV collider.
In addition to these two analyses, we also present a third, aimed at discovering pair produced higgsinos that decay to binos at a 100 TeV collider. Higgsinos and binos are new fermion states that arise in the Minimal Supersymmetric Standard Model (MSSM). This heavily- studied model is the minimal phenomenologically viable incorporation of supersymmetry - a symmetry that connects fermions and bosons - into the Standard Model. In the scenario we consider, the bino is the lightest supersymmetric partner, which makes it a good candidate for dark matter. Using razor variables and boosted decision trees, we are able to exclude Higgsinos up to 1.8 TeV for binos up to 1.3 TeV.
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Bouchart, Charles. "Phenomenology of the electroweak sector in warped (supersymmetric) extra-dimensional models." Paris 11, 2010. http://www.theses.fr/2010PA112331.
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On se place dans le cadre des modèles à dimension supplémentaire courbe adressant le problème de hiérachie de jauge. On considère ainsi le scenario suggéré par Randall et Sundrum sous l'hypothèse habituelle d'une symétrie de jauge custodiale étendue à l'espace total à 5 dimensions, permettant de protéger le modèle de trop larges corrections dans le secteur électrofaible, où le champ de Higgs est indépendament localisé sur ce qui est appelée la TeV-brane. Après avoir revu les bases de théorie des champs en dimensions supplémentaires, on introduit le cadre théorique des modèles RS, nous exposons en détail la construction de notre modèle phénoménologique, ainsi que les effets engendrés par la brisure de symétrie électrofaible sur notre modèle. Nous déterminons ensuite les diverses représentations minimales des multiplets de quarks sous la symétrie custodiale permettant de résoudre l'anomalie sur l'asymétrie avant-arrière du quark bottom. Il est ensuite montré en detail qu'il existe de fortes corrections à la valeur moyenne dans le vide du Higgs induites par de forts mélanges des bosons de jauge Z et W avec leurs exitations de KK. Le lien avec les tests de précision électrofaible est développé. Nous trouvons ainsi de substancielles corrections dûes à RS aux divers couplages au Higgs, pouvant affecter sa phénoménologie. La fin de cette thèse est dédiée aux extensions SupersSymétriques des modèles à dimension supplémenaire courbe, le champ de Higgs étant toujours confiné sur la TeV-braneLn the framework of warped extra dimension models addressing the gauge hierarchy problem, we consider the Randall-Sundrum scenario under the usual hypothesis of a bulk custodial symmetry protecting the model from large ElectroWeak corrections together with a Higgs field localized on the so-called TeV-brane. After reviewing the basics of field theory in extra dimensions, we introduce the RS framework, and show in details the construction of our phenomenological model as well as the effects of EW symmetry breaking. We determine the several minimal quark representations allowing to address the anomalies in the forward-backward b-quark asymmetry. It is then shown in details that there can exist large corrections to the Higgs boson Vacuum Expectation Value induced by mixings of the gauge bosons with their KK excitations. The connection with EW precision tests is developed. We find possibly substantial RS corrections to the various Higgs couplings able to affect its phenomenology. The end of this thesis is dedicated to SuperSymmetric extension of warped models, the Higgs field still being confined on the TeV-brane
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Bernon, Jérémy. "Caractérisation du secteur de Higgs et aspects du problème de la saveur." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY020/document.
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Le Modèle Standard (MS) de la physique des particules s’est imposé comme étant la description la plus précise des interactions fondamentales entre les particules élémentaires. La découverte d’un boson de Higgs, avec une masse de 125 GeV, en Juillet 2012 au Large Hadron Collider (LHC), en a marqué sa confirmation définitive. Cependant, de nombreux problèmes observationnels et théoriques sont au coeur du MS, la plupart liés au secteur de Higgs. Etant une particule scalaire, le boson de Higgs souffre de très grandes corrections radiatives, ce qui déstabilise l’échelle électro-faible et mène au problème de hiérarchie. L’un des buts principaux du LHC est d’explorer précisément le secteur de Higgs, afin de caractériser le mécanisme à l’origine de la brisure de la symétrie électro- faible et de tester de possibles solutions au problème de hiérarchie. Le secteur de Higgs est également responsable de la génération des masses des fermions dans le MS, par le biais des couplages de Yukawa. Ces couplages sont extrêmement non génériques et cela mène aux problèmes de la saveur au delà du MS.La première partie de cette thèse se concentre sur la caractérisation précise du secteur de Higgs. En particulier, le code public Lilith est présenté, il permet de dériver des contraintes sur des scénarios de nouvelle physique à l’aide des mesures des propriétés du boson de Higgs en collisionneurs. Une analyse des couplages du boson de Higgs dans le contexte de plusieurs scénarios est ensuite effectuée. Dans la seconde partie, la phénoménologie des modèles à deux doublets de Higgs est étudiée à la lumière des résultats de la première phase du LHC. La limite d’alignement, ainsi que la possible présence de bosons de Higgs légers, sont étudiées en détail. Finalement, dans la dernière partie de cette thèse, l’hypothèse de Violation Minimale de la Saveur est introduite comme une solution potentielle aux problèmes de la saveur au delà du MS. Appliquée au Modèle Standard Supersymétrique Minimal, l’évolution des couplages baryoniques violant la parité R sous le groupe de renormalisation est analysée en détailThe Standard Model (SM) of particle physics stands as the most successful description of the fundamental interactions between elementary particles. The discovery of a Higgs boson, at a mass of 125 GeV, in July 2012 at the Large Hadron Collider (LHC), marked its ultimate confirmation. However, various observational and theoretical problems lie in the heart of the SM, with the majority of them linked to the Higgs sector. Being a scalar, the Higgs boson is subject to very large radiative corrections and this ultimately leads to the electroweak hierarchy problem. One of the main goals of the LHC program is to precisely probe the Higgs sector, in order to characterize the mechanism at the origin of the breaking of the electroweak symmetry and test possible solutions to the hierarchy problem. The Higgs sector is also responsible for the generation of the fermion masses, as it induces the Yukawa couplings. The SM flavor sector is highly hierarchical and this leads to flavor puzzles in theories beyond the SM.The first part of this thesis is dedicated to the precise characterization of the Higgs sector. In particular, the public tool Lilith is presented, which allows to derive constraints on new physics models based on the Higgs measurements at colliders. It is then used to perform global fits of the Higgs couplings in the context of various scenarios. In the second part, the phenomenology of two-Higgs-doublet models is studied in the light of the results from the first run of the LHC. The so-called alignment limit is explored in detail, as well as the possible presence of light scalar states. Finally, in the last part of this thesis, the Minimal Flavor Violation hypothesis is introduced as a possible solution to the flavor puzzles beyond the SM. Enforcing it in the Minimal Supersymmetric Standard Model, the renormalisation group evolution of the baryonic R-parity violating couplings is then studied in detail
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Niehoff, Christoph [Verfasser], Martin [Akademischer Betreuer] [Gutachter] Beneke, and Andreas [Gutachter] Weiler. "Indirect Constraints on Composite Higgs Models and Leptoquarks / Christoph Niehoff ; Gutachter: Andreas Weiler, Martin Beneke ; Betreuer: Martin Beneke." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1136718974/34.
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Williamson, Sophie. "Phenomenology and collider constraints of Supersymmetric models in the Run 2 era of the LHC." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS417.
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Il a longtemps été pensé que le modèle standard (MS) est une description incomplète de notre univers, mais les résultats expérimentaux obtenus jusqu'à présent ne confirment rien de plus. La supersymétrie minimale, concrétisée par le modèle standard supersymétrique minimal (MSSM), est une extension compétitive du MS et a été bien étudiée, en particulier dans le contexte de modèles simplifiés, au niveau des collisionneurs. Cependant, les techniques de recherche actuelles n'utilisent peut-être pas de manière optimale la capacité du collisionneur à tester l'espace de paramètre accessible. Au lieu d'utiliser un veto statique sur le momentum du jet pour minimiser les processus d'arrière-plan indésirables dans les recherches de signaux, il peut être démontré que l'utilisation d'un veto au jet dynamique construit à partir de plusieurs mesures d'activité hadronique et leptonique peut augmenter le potentiel de découverte des balayages MSSM simplifiés. Dans le même temps, il est indéniable que les limites imposées aux modèles simplifiés ne représentent pas fidèlement des scénarios plus complexes - en particulier les modèles de supersymétrie non minimaux dans lesquels les signatures de désintégration sont modifiées par un spectre plus complexe de chargino et de neutralino. Les gauginos de Dirac (DG) constituent une extension non minimale bien motivée qui semble plus plausible que le MSSM, qui est de plus en plus constraint par les observations. Ce travail peut être divisé en deux parties: (1) il étudie comment le contenu en particules élargi des modèles DG peut modifier les limites actuelles de la masse de gluino et de squark du Run 2 du LHC, et (2) effectue une étude approfondie du secteur de Higgs dans de tels modèles, qui est automatiquement aligné en raison de la supersymétrie étendue qui relie les couplages de Yukawa aux couplages de jauge dans le secteur électrofaibleIt has long been thought that the Standard Model (SM) is an incomplete description of our universe, yet experimental results thus far do not confirm anything beyond it. Minimal supersymmetry, embodied by the minimal supersymmetric standard model (MSSM), is a competitive extension of the SM and has been well investigated, especially in the context of simplified models, at colliders. However, current search techniques may not be making optimal use of the collider's ability to test the accessible parameter space. Instead of using a static veto on jet momentum to minimise undesirable background processes in signal searches, it can be shown that employing a dynamic jet veto constructed out of several measures of hadronic and leptonic activity can heighten the discovery potential of simplified MSSM scans. At the same time, it cannot be denied that the limits placed on simplified models are not a true representation of more complex scenarios - especially non-minimal supersymmetry models where decay signatures are altered by a more complex chargino and neutralino spectrum. Dirac gauginos (DG) are a well-motivated non-minimal extension that restore the naturalness being lost by the ever more stringent constraints on the MSSM. Here this work looks down two avenues: it (1) investigates how the enlarged particle content of DG models can lead to altered bounds on current gluino and squark mass limits from Run 2 of the LHC, and (2) makes an in depth study of the Higgs sector in such models, which is automatically aligned owing to extended supersymmetry that links the Yukawa couplings to the gauge couplings in the electroweak sector
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Cano, Victor Manuel Peralta. "Phenomenology of Vector-like Fermions in Physics Beyond the Standard Model." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06122017-083800/.
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The Standard model of particle physics provides a successful theory to understand the experimental results of the electroweak and strong interactions. However, it does not have a satisfactory explanation for the hierarchy problem. Many extensions of the Standard Model that solve the hierarchy problem result in new particles. We will study the phenomenology of vector-like fermions resulting in theories where the Higgs boson is typically a pseudo-Nambu-Goldstone boson. In these theories we study the case where a heavy fermion will be heavier than a heavy gluon, and then the channel of a heavy fermion decaying into a color octet is considered. We study this phenomenology at high energy colliders, both the LHC as well as future machines.O modelo padrão de física de partículas fornece uma teoria bem-sucedida para entender os resultados experimentais das interações eletrofracas e fortes. No entanto, não tem uma explicação satisfatória para o problema de hierarquia. Muitas extensões do Modelo Padrão que resolvem o problema hierarquia resultam em novas partículas. Estudaremos a fenomenologia de férmions vetoriais resultando em teorias onde o bóson de Higgs é tipicamente um bóson pseudo-Nambu-Goldstone. Nessas teorias, estudaremos o caso em que um férmion pesado será mais pesado do que um glúon pesado, e então o canal de um férmion pesado decaindo em um octeto de cor é considerado. Estudamos esta fenomenologia em colisores de alta energia, tanto para o LHC quanto as futuras máquinas.
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Stangl, Peter Paul [Verfasser], Andreas [Akademischer Betreuer] Weiler, Andreas [Gutachter] Weiler, and Danny van [Gutachter] Dyk. "Direct Constraints, Flavor Physics, and Flavor Anomalies in Composite Higgs Models / Peter Paul Stangl ; Gutachter: Andreas Weiler, Danny van Dyk ; Betreuer: Andreas Weiler." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1155923545/34.
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Stangl, Peter Paul Verfasser], Andreas [Akademischer Betreuer] [Weiler, Andreas [Gutachter] Weiler, and Danny van [Gutachter] Dyk. "Direct Constraints, Flavor Physics, and Flavor Anomalies in Composite Higgs Models / Peter Paul Stangl ; Gutachter: Andreas Weiler, Danny van Dyk ; Betreuer: Andreas Weiler." München : Universitätsbibliothek der TU München, 2018. http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20180315-1431578-1-7.
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Fournel, Cedric. "Théories de jauge et connexions généralisées sur les algébroïdes de Lie transitifs." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4036/document.
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Connus des mécaniciens de la géométrie de Poisson, les algébroïdes de Lie transitifs sont ici étudiés du point de vue de leurs sections afin de développer un formalisme algébrique plus proche de celui développé par les théories de jauge. Ici, les algébroïdes de Lie transitifs s'apparentent à une généralisation des champs de vecteurs sur la variété de base. Ce mémoire de thèse a pour objet l'étude des connexions généralisées sur les algébroïdes de Lie transitifs et la construction de théories de jauge. Les connexions ordinaires sur les algébroïdes de Lie transitifs sont définies par des 1-formes de connexion de l'algébroïde de Lie à valeurs dans son noyau et vérifiant une contrainte de normalisation sur ce noyau. En relâchant cette contrainte, on construit l'espace des 1-formes de connexions généralisées qui se décomposent, à l'aide d'une connexion ordinaire de fond, comme la somme d'une connexion ordinaire et d'un paramètre purement algébrique définit sur le noyau. Dans l'esprit des théories Yang-Mills, une action invariante de jauge est définie comme la “norme” de la courbure associée à une connexion généralisée. De cette action, il découle un lagrangien composé des termes des théories de jauge de type Yang-Mills-Higgs : le terme cinétique associé aux champs de jauge et le terme de couplage minimal pour un champ tensoriel scalaire plongé dans un potentiel quartique. La réduction du groupe de symétrie de la théorie s'effectue par une redistribution des degrés de liberté dans l'espace fonctionnel des champs de la théorie. Il résulte de ces manipulations la définition d'une théorie de type Yang-Mills dont les bosons vecteurs sont des champs massifsTransitive Lie algebroids are usually studied from the point of view of the geometry of Poisson. Here, they are preferentially defined in terms of sections of fiber bundle in order to get close to the formalism of the gauge field theory. Then, transitive Lie algebroids can be seen as a generalization of vector fields on the base manifold. This PhD thesis is concerned with the study of generalized connections on transitive Lie algebroids and the construction of gauge theories. Ordinary connections on transitive Lie algebroids are defined as the subset of 1-forms on Lie algebroids with values in its kernel which fulfill a normalization constraint on this kernel. By relaxing this constraint, we build the space of generalized connection 1- forms. Using a background connection, we show that any generalized connections can be decomposed as the sum of an ordinary connection and a purely algebraic parameter defined on the kernel. As in Yang-Mills theories, we define a gauge invariant functional action as the “norm” of the curvature associated to a generalized connection. Then, the Lagrangian associated to this action forms a Yang-Mills-Higgs type model composed with the field strength associated to gauge fields and a minimal coupling with a tensorial scalar field embedded into a quartic potential. In the case of Atiyah Lie algebroids, the symmetry group of the theory can be reduced by using an appropriate rearrangement of the degrees of freedom in the functional space of fields. We thus obtain a Yang-Mills type theory describing massive vector bosons
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Hessenberger, Stephan [Verfasser], Wolfgang F. L. [Akademischer Betreuer] Hollik, Alejandro [Gutachter] Ibarra, and Wolfgang F. L. [Gutachter] Hollik. "Two-Loop Corrections to Electroweak Precision Observables in Two-Higgs-Doublet-Models / Stephan Hessenberger ; Gutachter: Alejandro Ibarra, Wolfgang F. L. Hollik ; Betreuer: Wolfgang F. L. Hollik." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1152006819/34.
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Ghosh, Aishik. "Simulation of the ATLAS electromagnetic calorimeter using generative adversarial networks and likelihood-free inference of the offshell Higgs boson couplings at the LHC." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP058.
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Depuis la découverte du boson de Higgs en 2012, les expériences du LHC testent les prévisions du modèle standard avec des mesures de haute précision. Les mesures des couplages du boson de Higgs hors résonance permettront d'éliminer certaines dégénérescences qui ne peuvent pas être résolues avec les mesures sur résonance, comme la sonde de la largeur du boson de Higgs, ce qui pourrait donner des indications pour la nouvelle physique. Une partie de cette thèse se concentre sur la mesure des couplages hors résonance du boson de Higgs produit par la fusion du boson vecteur et se décomposant en quatre leptons. Ce canal de désintégration offre une occasion unique de sonder le boson de Higgs dans son régime hors résonance grâce à des sections efficaces augmentées au-delà de 2Mz (deux fois la masse du boson Z) de la région des quatre leptons. L'importante interférence quantique entre le signal et les processus de fond rend le concept d'"étiquettes de classe" mal défini, et pose un défi aux méthodes traditionnelles et aux modèles génériques de classification par apprentissage machine utilisés pour optimiser une mesure de la force du signal. Une nouvelle famille de stratégies d'inférence sans fonction de vraisemblance basées sur l'apprentissage machine, qui exploitent des informations supplémentaires pouvant être extraites du simulateur, a été adaptée à un problème de mesure de la force du signal. L'étude montre des résultats prometteurs par rapport aux techniques de base sur un ensemble de données de simulation rapide avec Delphes. Dans ce contexte, on a également introduit le réseau aspiration, un algorithme d'adverse amélioré pour la formation tout en maintenant l'invariance par rapport aux caractéristiques choisies. Les mesures de l'expérience ATLAS reposent sur de grandes quantités de données simulées précisément. Le logiciel de simulation actuel de Geant4 est trop coûteux en termes de calculs pour supporter la grande quantité de données simulées nécessaires aux analyses futures prévues. Autre partie de cette thèse se concentre sur une nouvelle approche de la simulation rapide utilisant un réseau advers génératif (GAN). La simulation de gerbe en cascade du calorimètre complexe d'ATLAS est la partie la plus lente de la chaîne de simulation utilisant Geant4. Son remplacement par un réseau de neurones qui a appris la distribution de probabilité des gerbes de particules en fonction des propriétés des particules incidentes et de la géométrie locale du détecteur augmente la vitesse de simulation de plusieurs ordres de grandeur, même sur des CPU à cœur unique, et ouvre la porte à une accélération supplémentaire sur les GPU. L'intégration dans le logiciel ATLAS permet pour la première fois de faire des comparaisons réalistes avec des simulations rapides paramétrées "à la main''. L'étude est réalisée sur une petite section du détecteur (0,20<|η|<0,25) en utilisant des photons et compare les distributions en utilisant des échantillons simulés par le modèle autonome ainsi qu'après intégration dans le logiciel ATLAS avec des échantillons Geant4 entièrement simulés. Des leçons importantes sur les mérites et les inconvénients des différentes stratégies, profitent à l'objectif ultime de simuler l'ensemble du calorimètre ATLAS avec des modèles générateurs profonds. L'étude révèle également un problème inhérent à le GAN de Wasserstein basé sur une pénalité de gradient, et propose une solutionSince the discovery of the Higgs boson in 2012, experiments at the LHC have been testing Standard Model predictions with high precision measurements. Measurements of the off-shell couplings of the Higgs boson will remove certain degeneracies that cannot be resolved with the current on-shell measurements, such as probing the Higgs boson width, which may lead to hints for new physics. One part of this thesis focuses on the measurement of the off-shell couplings of the Higgs boson produced by vector boson fusion and decaying to four leptons. This decay channel provides a unique opportunity to probe the Higgs in its off-shell regime due to enhanced cross-sections beyond 2Mz (twice the mass of the Z boson) region of the four lepton mass. The significant quantum interference between the signal and background processes renders the concept of `class labels' ill-defined, and poses a challenge to traditional methods and generic machine learning classification models used to optimise a signal strength measurement. A new family of machine learning based likelihood-free inference strategies, which leverage additional information that can be extracted from the simulator, were adapted to a signal strength measurement problem. The study shows promising results compared to baseline techniques on a fast simulated Delphes dataset. Also introduced in this context is the aspiration network, an improved adversarial algorithm for training while maintaining invariance with respect to chosen features. Measurements in the ATLAS experiment rely on large amounts of precise simulated data. The current Geant4 simulation software is computationally too expensive to sustain the large amount of simulated data required for planned future analyses. The other part of this thesis focuses on a new approach to fast simulation using a Generative Adversarial Network (GAN). The cascading shower simulation of the complex ATLAS calorimeter is the slowest part of the simulation chain using Geant4. Replacing it with a neural network that has learnt the probability distribution of the particle showers as a function of the incident particle properties and local detector geometry increases the simulation speed by several orders of magnitude, even on single core CPUs, and opens to door the further speed up on GPUs. The integration into the ATLAS software allows for the first time to make realistic comparisons to hand-designed fast simulation frameworks. The study is performed on a small section of the detector (0,20<|η|<0,25) using photons and compares distributions using samples simulated by the model standalone as well as after integration into the ATLAS software against fully simulated Geant4 samples. Important lessons on the merits and demerits of various strategies, benefit the ultimate goal of simulating the entire ATLAS calorimeter with a few deep generative models. The study also reveals an inherent problem with the popular gradient penalty based Wasserstein GAN, and proposes a solution
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Bonjour, Filipe. "Extended defects in curved spacetimes." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4966/.
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This Thesis is concerned with three particular aspects of extended cosmic strings and domain walls in cosmology: their dynamics, gravitation and interaction with a black hole. In Chapter 3, we study the dynamics of an abelian-Higgs cosmic string. We find its equations of motion from an effective action and compare, for three test trajectories, the resulting motion with that observed in the Nambu-Gotō approximation. We also present a general argument showing that the corrected motion of any string is generically antirigid. We pursue the investigation of the dynamics of topological defects in Chapter 5, where we find (from integrability conditions rather than an effective action) the effective equations governing the motion of a gravitating curved domain wall. In Chapter 4 we investigate the spacetime of a gravitating domain wall in a theory with a general potential V(ɸ). We show that, depending on the gravitational coupling e of the scalar ɸ, all nontrivial solutions fall into two categories interpretable as describing respectively domain wall and false vacuum-de Sitter solutions. Wall solutions cannot exist beyond a value (^4)(_3)ɛmax, and vacuum-de Sitter solutions are unstable to decaying into wall solutions below ɛmax at ɛmax we observe a phase transition between the two types of solution. We finally specialize for the Goldstone and sine-Gordon potentials. In Chapter 6 we consider a Nielsen-Olesen vortex whose axis passes through the centre of an extremal Reissner-Nordstr0m black hole. We examine in particular the existence of piercing and expelled solutions (where the string respectively does and does not penetrate the black hole's horizon) and determine that while thin strings penetrate the horizon — and therefore can be genuinely called hair — thick strings are expelled; the two kinds of solution are separated by a phase transition.
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Le, Corre Solen. "Higgs boson phenomenology beyond the Standard Model." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1028.
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Suite à la découverte du boson de Higgs en Juin 2012 au Large Hadron Collider, l’accélérateur de particules situé à la frontière franco-suisse, l’étude du secteur scalaire des particules élémentaires a connu un regain d’intérêt. En particulier, le boson de Higgs étant une particule clef au sein du Modèle Standard des particules, les expérimentateurs étudient ses propriétés avec beaucoup de soin.Le Modèle Standard, dont le but est de décrire les interactions entre particules élémentaires, n’est cependant pas une théorie complète. En effet, en plus de quelques problèmes d’ordre théorique, certains phénomènes observés expérimentalement ne peuvent pas être expliqués par ce modèle. Les théoriciens en physique des particules cherchent donc à établir une nouvelle théorie venant le compléter et permettant d’expliquer pleinement les observations expérimentales.Cette thèse est axée sur l’étude du secteur scalaire de modèles au-delà du Modèle Standard des particules. J’ai plus particulièrement travaillé sur un modèle à deux doublets de Higgs – modèle purement effectif mais qui peut être inclus dans d’autres théories plus abouties – ainsi que sur un modèle construit comme une combinaison entre les théories déjà très proches de techicouleur et de Higgs composites, et ce dans le cas particulier d’une brisure de symétrie SU (4) ? Sp(4). J’ai étudié ce dernier modèle d’un point de vue effectif mais la théorie complète est capable depallier un certain nombre des limitations du Modèle Standard.Chacun de ces modèles inclut un secteur scalaire plus riche que celui du Modèle Standard et contient au moins une particule pouvant être assimilée au boson de Higgs découvert au LHC. J’ai réalisé l’étude phénoménologique de chacun de ces modèles et les ai confrontés à des contraintes tant théoriques qu’expérimentales – en particulier celles obtenues grâce aux études les plus récentes, portant sur le boson de Higgs et sur de potentielles particules scalaires additionnelles, réalisées par les équipes du LHC. Cela m’a permis de contraindre les paramètres libres des modèles et en particulier de restreindre les valeurs possibles pour la masse des autres particules scalaires, permettant de mieux cibler les zones où ces nouvelles particules, si elles existent, pourraient être détectées au LHC.Ces deux théories, bien que très contraintes par les données expérimentales, ne sont toujours pas exclues par les contraintes expérimentales les plus récentesFollowing the discovery of the Higgs boson in June 2012 at the Large Hadron Collider, the particle collider located beneath the France-Switzerland border, interest in the study of the scalar sector in elementary particle physics significantly increased. In particular, as the Higgs boson plays a very special role in the Standard Model of particle physics, experimentalists study its properties with great care.The goal of the Standard Model is to describe the interactions between elementary particles. However the theory is not quite complete. Indeed, in addition to some purely theoretical problems, a number of experimental observations cannot be explained by the Standard Model. Theorists are therefore looking for a more comprehensive theory able to fully explain the observations.This thesis is based on the study of the scalar sector of two different extensions of the Standard Model of particle physics. I have worked on the Two-Higgs Doublet Model – this model is purely effective but can be included in more comprehensive theories – as well as on a model based on a combination of Technicolor and Composite Higgs theories in the framework of the SU (4) ? Sp(4) symmetry breaking pattern. I studied the latter via an effective approach but the full theory is able to get rid of some of the pitfalls of the Standard Model.These two models include a scalar sector that is richer than the one found in the Standard Model and contain at least one particle which can be assimilated to the Higgs boson discovered at the LHC.I performed a phenomenological study for these two models and tested them against both theoretical and experimental constraints. In particular I used the latest studies on the 125 GeV Higgs boson and on possible additional scalars performed by the ATLAS and CMS collaborations. The application of all these constraints drastically reduced the available parameter space of the two models. In particular it narrowed the possible mass range of the additional scalars, allowing to know more accurately where to search them experimentally in order to prove or rule out their possible existence.As of today the two theories I worked on are still not excluded by the latest experimentaldata
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Silva, Paulo José Ferreira Porfírio da. "Modelo de dois dubletos de higgs." Universidade Federal da Paraíba, 2013. http://tede.biblioteca.ufpb.br:8080/handle/tede/5756.
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In this dissertation we did a complete review of the StandardModel(SM), emphasizing the weak interactions, this in order to treat an extension of theMP with addition of a doublet of scalar theory, known in the literature asModel with Two Higgs doublets (2HDM). We will treat this model from the point of view of both aspects: when two doublets develop the expected value of the vacuum(vev) and when only one develops doublets vev, utilize the potential of 2HDM does not violate CP. These two models are particularly important because they are quite simple and can solve some problems that are open in Physics, one of the most important is the dark matter (DM). Furthermore, we will use the formalism of oblique parameters, radiative corrections involving first order, to parameterize the effects of New Physics (NP). We will present the phenomenology to obtain 2HDMI and regions that are in agreement with the experimental data.
Nesta dissertação fizemos uma revisão completa doModelo Padrão (MP), dando ênfase as interações fracas, isto com o intuito de tratarmos de uma extensão do MP com adição de um dubleto de escalar a teoria, conhecida na literatura como Modelo com Dois Dubletos de Higgs(2HDM)1. Iremos tratar deste modelo sob o ponto de vista de dois aspectos: quando os dois dubletos desenvolvem valor esperado do vácuo(vev) e quando apenas um dos dubletos desenvolve vev, utilizamos o potencial do 2HDM que não viola CP. Particularmente, esses dois modelos são importantes porque eles são bastante simples e podemresolver alguns problemas que estão emaberto na Física, um dosmais importantes é amatéria escura(ME). Além disso, iremos utilizar o formalismo de parâmetros oblíquos, que envolve correções radiativas de primeira ordem, para parametrizar os efeitos da Nova Física(NF). Apresentaremos a fenomenologia para o 2HDMI e obteremos as regiões que estão de acordo com os dados experimentais.
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Quevillon, Jérémie. "Higgs Physics Beyond the Standard Model." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01070196.
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On the 4th of July 2012, the discovery of a new scalar particle with a mass of order 125 GeV was announced by the ATLAS and CMS collaborations. An important era is now opening: the precise determination of the properties of the produced particle. This is of extreme importance in order to establish that this particle is indeed the relic of the mechanism responsible for the electroweak symmetry breaking and to pin down effects of new physics if additional ingredients beyond those of the Standard Model are involved in the symmetry breaking mechanism. In this thesis we have tried to understand and characterize to which extent this new scalar field is the Standard Model Higgs Boson and set the implications of this discovery in the context of Supersymmetric theories and dark matter models.In a first part devoted to the Standard Model of particle physics, we discuss the Higgs pair production processes at the LHC and the main output of our results is that they al-low for the determination of the trilinear Higgs self-coupling which represents a first important step towards the reconstruction of the Higgs potential and thus the final verifica-tion of the Higgs mechanism as the origin of electroweak symmetry breaking.The second part is about Supersymmetric theories. After a review of the topics one of our result is to set strong restrictions on Supersymmetric models after the Higgs discov-ery. We also introduce a new approach which would allow experimentalists to efficiently look for supersymmetric heavy Higgs bosons at current and next LHC runs.The third part concerns dark matter. We present results which give strong constraints on Higgs-portal models. We finally discuss alternative non-thermal dark matter scenario. Firstly, we demonstrate that there exists a tight link between the reheating temperature and the scheme of the Standard Model gauge group breaking and secondly we study the genesis of dark matter by a Z' portal.
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Madeira, Rômulo Brandão. "Largura do bóson de Higgs em dois fótons em modelos além do modelo padrão." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-11112016-003950/.
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Nesta dissertação, revisamos o desenvolvimento do mecanismo de Higgs e a sua importância para a estruturação do Modelo Padrão da física de partículas elementares sob um ponto de vista histórico e contemporâneo. Foi enfatizado como a introdução de um dubleto escalar complexo com as simetrias de gauge do modelo fez com que algumas partículas adquirissem massa. Foi apresentado o contexto da descoberta do bóson de Higgs consumada em 2012 e possíveis discrepâncias nos resultados obtidos no Large Hadron Collider que poderiam indicar a possibilidade de física nova, em especial no canal de decaimento H . Estudamos as contribuições para a largura deste bóson em dois fótons com a introdução de novas partículas fermiônicas e escalares. Uma síntese do cálculo da largura deste canal, assim como as técnicas envolvidas para realizá-lo, são apresentadas. Considerando apenas as duas contribuições dominantes, foi estimado um valor de 9,165 keV para a largura do decaimento, resultando em uma razão de ramificação de 2,24 · 10^.In this dissertation, we review the development of the Higgs mechanism and its importance to the structure of the Standard Model of elementary particles physics from a historical and contemporary point of view. It was emphasized how the introduction of a complex scalar doublet with the gauge symmetries of the model induces some particles to acquire mass. It was presented the context of Higgs boson discovery accomplished in 2012 and possible discrepancies in the results obtained at the Large Hadron Collider which may indicate the possibility of new physics, in particular in the H decay channel. We studied the contributions to the width of this boson decay into two photons with the introduction of new fermionic and scalar particles. A synthesis of computation of this channel width, as well as techniques involved to accomplish it, are presented. Considering the only two dominant contributions, it was estimated a value of 9.165 keV for the decay width, resulting in a branching ratio of 2.24 · 10^{3}.
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Kallarackal, Jim. "The Higgs boson resonance from a chiral Higgs-Yukawa model on the lattice." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16332.
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Das Higgs-Teilchen ist essentiell für die Erzeugung von Massen für Fermionen und Eich- bosonen der schwachen Wechselwirkung. Ziel dieser Arbeit ist es, die Masse und die Zerfallsbreite des Higgs-Teilchens einzugrenzen. Grundlage für die Berechnung physikalischer Größen ist dabei das Pfadintegral, welches mittels Monte-Carlo Simulationen bestimmt wird. Ein polynomieller Hybrid-Monte- Carlo-Algorithmus berücksichtigt dabei alle dynamischen Freiheitsgrade der Fermionen. Die chirale Natur der Fermionen werden mit Hilfe des Neuberger- Overlap-Operators beschrieben. In dieser Arbeit wird das Standardmodell auf den Higgs-Yukawa-Sektor eingegrenzt, welcher keine Eichbosonen enthält und lediglich ein degeneriertes Quark-Doublet berücksichtigt. Anhand des Higgs-Teilchen-Propagators werden die Ergebnisse aus der Git- terstörungsrechnung bis zu einer Schleife mit denen aus der Monte-Carlo- Simulation verglichen. Für die untersuchten Parameter, stimmen die Ergeb- nisse aus der Störungstheorie mit den Monte-Carlo-Daten sehr gut überein. Ein Schwerpunkt dieser Arbeit ist die Analyse der Resonanzparameter des Higgs-Teilchens. Die Resonanzmasse und die Resonanzbreite werden bei schwachen als auch bei starken quartischen Kopplungen untersucht. Das Higgs-Teilchen erscheint nicht als asymptotisch stabiles Teilchen, sondern als Resonanz. In allen Fällen liegt die Resonanzbreite unter 10% der Resonanzmasse. Die Resonanzmasse wird sodann mit der Propagatormasse verglichen. Für alle betrachteten Kopplun- gen gibt es eine hervorragende Übereinstimmung beider Größen. Zuletzt gilt es, den Einfluss einer schweren vierten Generation von Quarks auf die obere und untere Massenschranke des Higgs-Teilchens zu untersuchen. Alle numerischen Resultate involvieren eine umfassende Analyse der Volu- menabhängigkeit und erfordern zwingend eine Extrapolation ins unendliche Volumen.The Higgs boson is a central part of the electroweak theory and is crucial to generate masses for fermions and the weak gauge bosons. The goal of this work is to set limits on the mass and the decay width of the Higgs boson. The basis to compute the physical quantities is the path integral which is here evaluated by means of Monte Carlo simulations thus allowing for fully non perturbative calculations. A polynomial hybrid Monte Carlo algo- rithm is used to incorporate dynamical fermions. The chiral symmetry of the electroweak model is incorporated by using the Neuberger overlap operator. Here, the standard model is considered in the limit of a Higgs-Yukawa sector which does not contain the weak gauge bosons and only a degenerate doublet of top- and bottom quarks are incorporated. Results from lattice perturbation theory up to one loop of the Higgs boson propagator are compared with those obtained from Monte Carlo simulations. At all values of the investigated couplings, the perturbative results agree very well with the Monte Carlo data. A main focus of this work is the investigation of the resonance parameters of the Higgs boson. The resonance width and the resonance mass are investigated at weak and at large quartic couplings. The Higgs boson does not appear as an asymptotic stable state but as a resonance. In all considered cases the Higgs boson resonance width lies below 10% of the resonance mass. The obtained resonance mass is compared with the mass obtained from the Higgs boson propagator. The results agree perfectly at all values of the quartic coupling considered. Finally, the effect of a heavy fourth generation of fermions on the upper and lower Higgs boson mass bound is studied. All numerical results presented in this work involve extensive finite volume analysis and an extrapolation to infinite volume is inevitable.
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Riembau, Marc. "Exploration of the higgs sector after its discovery." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/663947.
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El descobriment del bosó de Higgs és la culminació d’una recerca que ha
durat 40 anys, i completa un marc teòric sota el qual gairebé totes del
dades obtingudes de col·lisionadors de partícules poden ser explicades consistentment.
Simultàniament, i paradoxalment, l’aparent con rmació d’una
separacó d’escales entre l’electrofeble i la que suposadament estabilitza la
masa del bosó de Higgs posa el relleu el problema de la jerarquia. En la
recerca d’una descripció del món que simpli qui els patrons i simetries del
Model Estàndard, l’exploració de l’escala dels TeVs i en particular l’estudi
del bosó de Higgs tindran un paper central. En aquesta tesi presentem les
possibilitats que el LHC i futurs col·lisionadors proveiran, amb énfasi en la
determinació de l’auto-acoblament del bosó de Higgs. També considerarem
l’estudi de la producció de bosons electrofebles com a eina per entendre les
interaccions dels bosons de Golstone que formen part del doblet de Higgs,
mostrant la seva rellevància al combinar-ho amb les dades del pol de la Z
i altres cerques al LHC. Finalment, ens centrem en com el moment dipolar
elèctric de l’electró posa fortes restriccions en models on el bosó de Higgs
és descrit com un estat compost.The discovery of the Higgs boson culminates a 40-year long hunt and completes a theoretical framework under which almost all collider data can be consistently explained. At the same time, paradoxically, the con rmation of an apparent mass gap above the electroweak scale exacerbates the problem of the electroweak hierarchy. In the search of a description of the world that simpli es the patterns and symmetries of the Standard Model, the exploration of the TeV scale and in particular the study of the Higgs boson will play a central role. In this thesis we explore the possibilities that the LHC and future colliders will bring, with particular emphasis on the determination of the Higgs self-coupling. We also consider the pair production of electroweak bosons as a probe of the Goldstone interactions in the Higgs doublet, and show its relevance as a way to improve the Z pole measurements and its interplay with other LHC searches. Finally, we focus on how the electron’s electric dipole moment can set strong constraints on models where the Higgs arises as a composite state.
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Correia, Fagner Cintra [UNESP]. "Física de sabores e modelos multi-Higgs." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/108884.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O modelo331 mínimo consiste em uma extensão ao Modelo Padrão amparada em SU'(3) IND.L' ? U'(1) IND. X'. Os férmions se transformam como tripletos ou anti-tripletos de SU'(3) IND. L' com componentes envolvendo quarks exóticos e partículas conhecidas da fenomenologia atual. Nosso objetivo aqui é explorar qualidades adicionais e limitar novos parâmetros do 331 a partir de processos que violem sabor, como a mistura de mésons neutros
The minimal 331 model has been proposed as an extension of the Standard Model based on the gauge group SU'(3) IND. L' ?U'(1) IND.X'. In this model, the left-handed fermions transform as triplets (or anti-triplets) under the action ofSU'(3) IND. L', whose generations correspond to the known SM fermions and new heavy quarks. Our purpose here is to constrain the 331 parameters considering the limits of ?avour changing processes as meson mixing
FAPESP: 11/16636-6
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Correia, Fagner Cintra. "Física de sabores e modelos multi-Higgs /." São Paulo, 2013. http://hdl.handle.net/11449/108884.
Full textAbstract:
Orientador: Vicente PleitezBanca: Jairo Alexis Rodríguez López
Banca: Orlando Luis Goulart Peres
Resumo: O modelo331 mínimo consiste em uma extensão ao Modelo Padrão amparada em SU'(3) IND.L' ⊗ U'(1) IND. X'. Os férmions se transformam como tripletos ou anti-tripletos de SU'(3) IND. L' com componentes envolvendo quarks exóticos e partículas conhecidas da fenomenologia atual. Nosso objetivo aqui é explorar qualidades adicionais e limitar novos parâmetros do 331 a partir de processos que violem sabor, como a mistura de mésons neutros
Abstract: The minimal 331 model has been proposed as an extension of the Standard Model based on the gauge group SU'(3) IND. L' ⊗U'(1) IND.X'. In this model, the left-handed fermions transform as triplets (or anti-triplets) under the action ofSU'(3) IND. L', whose generations correspond to the known SM fermions and new heavy quarks. Our purpose here is to constrain the 331 parameters considering the limits of flavour changing processes as meson mixing
Mestre
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Rocha, Leandro Seixas. "Um estudo sobre modelos de Little Higgs : o modelo mais simples e seu singleto escalar." reponame:Repositório Institucional da UFABC, 2009.
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Lindahl, Viveca. "Detection Prospects of Doubly Charged Higgs Bosons from the Higgs Triplet Model at the LHC." Thesis, Uppsala universitet, Högenergifysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-155961.
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In this thesis I explore the possibilities of detecting doubly charged Higgs bosons from the Higgs Triplet Model (HTM) at the Large Hadron Collider (LHC) at CERN. Higgs bosons are included into the Standard Model (SM) of particle physics in order to explain the origin of mass of the elementary particles. Even though the SM is considered to be a reliable starting point for any particle theory, no Higgs particles have to this day been found. There are therefore high expectations for the record-breaking energies of the LHC to lead to a Higgs discovery. The HTM produces seven different Higgs bosons, and among these we find the doubly charged ones. Because of their exotic charge, I focus on studying these Higgs particles in particular. To this purpose, I implement the full HTM theory as an alternative model option in standard particle physics Monte-Carlo software and then simulate LHC proton-proton collisions at a center of mass energy of 14 TeV. The investigated signal is defined as two like-signed leptons, four hard jets and missing energy in the final state. The main production mechanisms are pair-production and associated production with a singly charged Higgs. Since I choose to study a region of parameter space where the triplet vacuum expectation value is relatively large, the doubly charged Higgs decays into W's and the singly charged Higgs into WZ or tb. The results of the simulations show that the LHC could probe Higgs masses up to at least 300 GeV with an integrated luminosity of about 300 fb.1.
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Thrasher, Richard Keith. "Extensions of the Standard Model Higgs Sector." W&M ScholarWorks, 2018. https://scholarworks.wm.edu/etd/1550153848.
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The Standard Model is regarded as one of the most successful scientific theories, but there is compelling evidence that it is an incomplete theory of particle physics. There is currently no understanding of the observed baryon asymmetry, the nature of dark matter, and dark energy. Field theoretic considerations indicate parameters in the Standard Model are extremely fine-tuned. This suggests the existence of new physics, accessible at higher energies, to explain these seemingly unnatural tunings. to solve these puzzles, and others not addressed by the Standard Model, many extensions of the Standard Model have been proposed. It is of great importance that we fully understand the effects these models have on Standard Model physics and how these theories can be tested. in this dissertation we explore the phenomenology associated with beyond the Standard Model physics, specifically focusing on models with extended Higgs sectors. in chapter 2, we study two classes of lepton flavor violating two Higgs doublet models. Chapter 3 explores a model where the Higgs is a pseudo-Goldstone boson of a non-abelian orbifold projection and all other low energy states carry no Standard Model charges. Chapters 4 and 5 study Higgs phenomenology in the context of a warped five dimensional space-time. The former analyzes the effects of Higgs-radion mixing in two Higgs doublet models. The latter reviews a previous proposal where the Higgs doublet takes the role of a bulk stabilizer. The result is a model containing a single Higgs-radion state. in the final chapter, we present a higher derivative extension of the type-I and II two Higgs doublet models. The resulting theory gives rise to unusual partner states containing negative kinetic energy terms.
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Kling, Felix, Jose Miguel No, and Shufang Su. "Anatomy of exotic Higgs decays in 2HDM." SPRINGER, 2016. http://hdl.handle.net/10150/622345.
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Large mass splittings between new scalars in two-Higgs-doublet models (2HDM) open a key avenue to search for these new states via exotic heavy Higgs decays. We discuss in detail the different search channels for these new scalars at the LHC in the presence of a sizable mass splitting, i.e. a hierarchical 2HDM scenario, taking into account the theoretical and experimental constraints. We provide benchmark planes to exploit the complementarity among these searches, analyzing their potential to probe the hierarchical 2HDM parameter space during LHC Run 2.
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Dias, Otávio Augusto Trivério. "Escalares de Higgs e decaimentos leptônicos /." São Paulo, 2004. http://hdl.handle.net/11449/132575.
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Orientador: Vicente PleitezBanca: Mauro Donizeti Tonasse
Banca: Marcos Cardozo Rodriguez
Resumo: É estudado o decaimento do 'mü'- em dois diferentes modelos com simetrias de gauge 'SU(3) IND. c' X 'SU(3) IND. L' X 'U(1) IND. N'. Estes modelos coincidem com o modelo padrão a baixas energias, prevêem a existência de bósons de gauge bileptônicos e usualmente tem um setor escalar mais rico que o existente no modelo padrão. Fazendo uma redefinição da constante de Fermi, pode ser delimitada a massa do bóson de gauge dileptônico que aparece nos dois modelos e também é delimitada a massa de um escalar de Higgs
Abstract: We consider the 'mü'- leptonic decay in two different gauge models with 'SU(3) IND. c' X 'SU(3) IND. L' X 'U(1) IND. N' gauge symmetries. These models coincide with the standard model at low energies, predict the existence of bileptonic gauge bosons and its scalar sector is richer than the standard model one's. By redefining the Fermi constant, a limit for the bileptonic gauge boson may be set and, in case the new gauge boson is much heavier than the Higgs particle, a limit for the scalar may also be set
Mestre
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Ciccolini, Mariano L. "Standard Model Higgs boson phenomenology at hadron colliders." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/13398.
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In this thesis two different aspects of Standard Model Higgs boson phenomenology at hadron colliders are addressed. A precise theoretical knowledge of production cross sections is needed in order to assist in the Higgs boson search efforts of the experimental community. Consequently, the next-to-leading-order electroweak corrections to Higgs boson production in association with a vector boson at hadron colliders have been calculated. Significant corrections were found, and theoretical uncertainties were analysed. In addition to production cross sections, a deep knowledge of background processes is also needed, especially at hadron colliders. The gluon-induced contributions to offshell W-boson pair production have been calculated. The invariant amplitude has been used to calculate the contribution from gluon initiated processes to the non-resonant W-boson pair production background to the Higgs boson search channel at the CERN LHC. These contributions are evaluated in the approximation of massless quarks circulating the loops. These results were used to study the effect of experimental cuts proposed to increase the signal to background ratio of the above mentioned search channel.