Avec la recherche de nouvelles particules dont le Higgs, la mesure précise des caractéristiques du boson W était un des objectifs majeurs de l'accélérateur LEP. Par exemple, la production de 10.000 événements par expérience dans l'état final W+W- qui peuvent être complètement reconstruits permet de mesurer la masse du boson W avec une précision relative de 10^-4. Dans ce document, je m'intéresse plus particulièrement aux couplages du boson W aux particules Z et gamma. La théorie électrofaible basée sur le groupe de symétrie SU(2)_LxU(1)_Y prédit l'existence, à l'arbre, des vertex WWZ et WWgamma. Leur existence est confirmée par la mesure de la section efficace de production de paires de W au LEP. Les valeurs effectives de couplages sont modifiées par l'introduction de boucles de particules du Modèle Standard au niveau du vertex (effet de 10^-3). Ces boucles pouvant aussi inclure des particules au delà de ce modèle, elles induisent des déviations (de l'ordre de 10^-3 pour la plupart des modèles). Elles sont décrites par 14 paramètres complexes. Leur mesure permet la recherche indirecte de nouvelles particules. Toutefois, au LEP, le nombre d'événements n'est pas suffisant pour pouvoir les mesurer simultanément. L'analyse se restreint donc aux trois paramètres les plus prometteurs : g1z, kappa_gamma et lambda_gamma. Au LEP, les événements sensibles à ces couplages sont les états finaux WW et Wenu. Leurs sections efficaces de production totales et différentielles sont les variables utilisées pour extraire la valeur des couplages. Bien qu'ayant des précisions différentes, l'ensemble de leurs canaux de désintégrations sont analysés. La précision sur ces mesures est principalement apportée par l'analyse des distributions angulaires de l'état final WW ->l nu qq. L'ensemble des données collectées par l'expérience ALEPH sont traitées. Les résultats présentés sont les valeurs finales publiées par l'expérience. Une précision de l'ordre de 10^-2 est obtenue dominée par l'erreur statistique. La combinaison des mesures des quatre expériences LEP permet donc de réduire cette erreur d'un facteur 2. Ce document finit par une description des mesures qui seront faites aux prochains collisionneurs (LHC et collisionneurs linéaires e^+e^-). Les précisions attendues (~10^-4) donneront des indications sur la présence de nouvelles particules jusqu'à des échelles d'énergie de 10 TeV.

Cette thèse aborde deux problèmes ayant trait à la physique des gaz quantiques de basse dimensionnalité. Le premier système étudié est un mélange unidimensionnel de bosons et de fermions sans spin soumis à un potentiel aléatoire. Nous commençons par écrire un Hamiltonien de basse énergie et abordons la question de la localisation du point de vue de l'accrochage des ondes de densité par un désordre faible. En utilisant le Groupe de Renormalisation et une méthode variationnelle dans l'espace des répliques, le diagramme de phase peut être tracé en fonctions de deux paramètres : la force des interactions Bose-Bose et Bose-Fermi. La position et les propriétés des phases dépendent d'un paramètre additionnel, le rapport des vitesses du son de chaque composante du gaz. Quelque soit la valeur de ce rapport nous trouvons trois phases, (i) une phase totalement délocalisée, le liquide de Luttinger à deux composantes, (ii) une phase totalement localisée où les deux composantes sont accrochées par le désordre et (iii) une phase intermédiaire où seuls les fermions sont localisés. Le deuxième système est un gaz de bosons de cœur dur sur un réseau en échelle. Trois paramètres en contrôlent la physique : les amplitudes de saut transverse et longitudinale, et le remplissage. En utilisant plusieurs méthodes analytiques (théorie des perturbations, bosonisation et RG) nous proposons une interprétation de résultats numériques nouveaux obtenus par nos collaborateurs, notamment sur le paramètre de Luttinger du mode symétrique. Nous en déduisons un diagramme de phase en présence de désordre faible.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 100-103).

Les bosons chargés identiques confinés dans une grande boite dont les parois portent une charge de signe contraire mais de même densité assurant la neutralité du système, constituent un plasma neutre à une composante. On obtient un plasma neutre à deux composantes lorsque les bosons identiques de charge positive et ceux de charge négative de même densité sont contenus dans la même boite. Le plasma non-neutre des bosons s'obtient en confinant l'assemblée des bosons identiques chargés dans un piège des particules chargées de Penning ou de Paul. Nous avons fait l'étude théorique de la dégénérescence quantique du plasma non-neutre des bosons de spin zéro confinés dans un piège de Paul à haute densité et à très basse température. Cette étude a porté d'abord sur un système sans transition de phase dans le piège, et ensuite sur le régime gazeux (de Mathieu) et sur le régime intermédiaire (liquide). Nous avons utilisé la théorie microscopique en considérant le champ scalaire complexe ou champ des mésons chargés pour construire les opérateurs bosons chargés de spin zéro, définir l'espace des états quantiques du système, construire les opérateurs champs de création et d'annihilation des bosons d'impulsion p au point r . Ces derniers nous ont permis de construire l'opérateur Hamiltonien de la seconde quantification du plasma et la matrice densité à une particule. La matrice densité du plasma non neutre de bosons de spin zéro et la prescription de Bogoliubov révèlent l'occupation macroscopique d'un état quantique dans le piège harmonique radiofréquence de Paul. Nous avons déterminé pour ce plasma l'énergie de l'état fondamental, le spectre des excitations élémentaires, l'équation de Hartree-Fock etc. Nos résultats sont comparés dans un tableau aux résultats de l'application de la théorie microscopique aux assemblées des bosons neutres confinés dans un piège magnétique et au gaz électronique.

We present in this thesis a detailed analysis of Higgs boson interactions at future colliders. In particular we examine, in a model independent way, the sensitivity of an Linear Collider in probing the interaction of Higgs boson with a pair of vector bosons with/without the use of polarized initial beams and/or the information on final state fermion polarization. We devise several observables which have definite transformation properties under discrete symmetry operations to constrain the different anomalous parts of the Higgs boson interactions having the same transformation properties. We also investigate effects of initial state radiation (ISR) and beamstrahlung on probes of anomalous Higgs boson couplings at higher center of mass energies. We begin the first chapter with an introduction of the Standard Model (SM) of particle physics. We mainly focus on the Higgs sector of the SM. In this chapter we review the electroweak (EW) symmetry breaking mechanism, viz. the Higgs mechanism, responsible for generating masses of all the particles in the SM. We briefly summarize the high precision tests of the SM. We discuss constraints on the mass of the SM Higgs boson derived from theoretical considerations such as stability of the electroweak vacuum, unitarity in scattering amplitudes, perturbativity of the Higgs self-coupling and no fine-tuning in the radiative corrections in the Higgs sector. Next we present the experimental bounds on the mass of the SM Higgs boson obtained from the direct searches of the Higgs boson at LEP and from the electroweak high precision measurements. We then discuss the importance of a general model independent approach to study properties of the Higgs boson and to verify the uniqueness of the SM. In the context of low energy effective theory, this analysis can be made by using the effective Lagrangian that contains higher dimensional operators. We conclude this chapter giving examples of dimension-6 operators which can contribute to the anomalous Higgs boson interactions that we analyze in this thesis. Second chapter contains the dominant Higgs boson production processes at an collider.In a model independent analysis we consider the effects of the most general ¯ (V = W Z) vertex, consistent with Lorentz invariance, for the process where f is any light fermion. This vertex also includes the possibility of CP violation and can be written as: where ki denote the momenta of the two W’s (Z’s), ǫναβis the antisymmetric tensor with ǫ0123 = 1. Previous studies showed that the squared matrix element of the process e+e−ZH does not include all the anomalous parts of a general ZZH vertex. Also it is obvious that one cannot analyse anomalous WWH couplings using this process. Hence we consider the full process e+e−ffH to probe all the anomalous parts of the VVH vertex. We devise a general and very elegant procedure to probe these couplings at an e+e−collider. We construct various combinations by taking dot and scalar triple product of momenta of initial and final state particles. These combinations have definite transformation properties under CP and naive time reversal (T˜)transformations. Hence the corresponding observables constructed using expectation value of sign of these combinations can probe a specific part of the anomalous VVH couplings whose coefficient in the effective Lagrangian has same transformation properties. We investigate the possible sensitivity to which the anomalous VVH couplings can be probed at a Linear Collider using these observables in the process e+e−ffH for unpolarized beams [1, 2]. We consider the case of a Linear Collider, operating at center of mass energy of 500 GeV, with an integrated luminosityof 500 fb−1 and assume a Higgs boson of mass 120 GeV. We impose various kinematical cuts on different final state particles to reduce backgrounds ¯and consider the events where H decays into bb with branching ratio 0.68. We can enhance or suppress the effect of the s-channel, Z-exchange diagram by imposing cut on the ¯invariant mass of the ff system. We use b-tagging efficiency to be 70%; a value expected to be possible in the collider environment. We first consider asymmetries involving either the polar or azimuthal angular distributions. Then we combine these informations to construct combined polar-azimuthal asymmetries in order to enhance the sensitivity. We obtain strong constraints on most of the anomalous parts of the ZZH vertex using cross section and these asymmetries. The process e+eν¯ −νH has two missing ν’s in the final state. Hence their momenta are not available to construct any observables. Therefore, direct probes for T˜-odd WWH couplings viz. ℑ(bW), ℜ(˜bW), cannot be constructed and only weak, indirect bounds are possible. Further, without using polarized beams the contamination from the ZZH vertex cannot be eliminated in the determination of WWH couplings. In the third chapter we analyze use of linearly polarized e+/e−beams and/or information on final state lepton polarization in probingthe interaction of the Higgs boson with a pair of vector bosons[3, 4]. We make several combinations of different particle momenta and spins. We then define observables as expectation values of signs of these combinations for longitudinally polarized beams and/or for production of final state τ’s with a definite helicity state. Use of polarization allows us to devise more observables as compared to the unpolarized case. We list the observables for which use of polarization affords a distinct gain in sensitivity. In our analysis we divide the total luminosity of 500 fb−1 equally among different polarization states of initial state e−/e+ and take the values 80% and 60% for e−/e+ respectively, foreseen at the ILC. We construct numerical combinations of various linearly polarized cross sections to enhance the contribution of ℜ(bZ) while getting rid of ΔaZand vice versa. It is necessary to construct such combinations of cross section as ℜ(bZ), ΔaZhave same CP and T˜transformation properties and hence there are no asymmetries that can be constructed to probe them individually. With these combinations it is possible to probe both these CP-and T˜-even couplings cleanly, using linearly polarized beams. We find that longitudinal beam polarization can improve the sensitivity to CP-odd ZZH couplings viz. ℜ(˜bZ), ℑ(˜bZ), by a factor of about 6 −7. We also construct observables for final state τ’s with definite helicity. We make a plausible assumption that it should be possible to isolate events with τ’s in definite helicity state with an efficiency of 40%. With this assumption we demonstrate that the use of final state τ polarization can improve the sensitivity to the CP-even and T˜-odd ZZH coupling (ℑ(bZ)) by a factor of about 3. Moreover use of final state τ-polarization measurement along with linearly polarized beams can improve the sensitivity for one of the CP-odd ZZH couplings (ℜ(˜bZ))bya factor of about 2.Use of longitudinally polarized beams can also help to reduce the contamination in the measurement of the WWH couplings coming from the ZZH vertex contribution. We also perform χ2-analysis using the observables for different polarizations. The cross section of the t–channel diagram increases with increasing center of mass energy. Therefore, off hand it may look like that going to higher energy can increase the sensitivity to WWH couplings. Hence in this chapter we further investigate possible gain in sensitivity going to higher center of mass energies[3, 4]. We use the same observables constructed with unpolarized beams and consider various center of mass energies ranging from 300 GeV to 3 TeV. We find that it is possible to increase the bZ)byabouta factor 2 1 TeVas compared to the case of 500 GeV. In this analysis we include the effects of initial state radiation (ISR) and beamstrahlung. Both the ISR and beamstrahlung =500 GeV, the ISR can affect cross sections for s–channel processes by 10−15%.However, we observe that the effects of ISR and beamstrahlung change both the SM and anomalous contributions more beneficial for the study of anomalous V V H couplings. In the last chapter we investigate the role of transversely polarized beams to constrain the anomalous V V H couplings[5]. Using transverse spin direction of e±it is possible to devise observables which are nonzero only for transversely polarized beams. Use of transverse beam polarization allows construction of completely independent probes of both the CP-and T˜-even anomalous ZZH couplings (ΔaZ, ℜ(bZ)), leading to independent determination of all the anomalous parts of the ZZH vertex. In addition the use of transverse beam polarization can also add to the sensitivity for one of the CP-odd ZZH couplings viz. ℜ(˜bZ). Measurement of final state τ-polarization with transversely polarized beams can in fact also offer improvement on the sensitivity for ℑ(bZ) which is even under CP-and odd under T˜-transformation. Use of transverse beam polarization cannot improve the bounds on the anomalous WWH couplings as the squared matrix element of the t– channel WW–fusion diagram does not have any transverse beam polarization dependent term. A summary of the results obtained in this thesis is follows. We have developed a general procedure to construct observables with specific CP and T˜transformation properties to probe various anomalous couplings of the Higgs boson to a pair of vector bosons (V = W/Z) at an e+/e−Linear Collider. We investigate probes of these couplings in the process e+e−ffH. This process gives access to those anomalous couplings which cannot be probed using angular distribution of the Z boson in the process e+eZH. We showed that it would be possible to obtain stringent bounds on some of the parts of the anomalous ZZH vertex even without using polarized beams and/or information on polarization of final state particles. Use of longitudinal beam polarization and/or final state τ polarization can significantly enhance the sensitivity in probing most of the anomalous parts of a general ZZH vertex. Use of longitudinal beam polarization also reduces the contamination from the ZZH couplings in the determination of the ˜T-even anomalous WWH couplings (ℜ(bW), ℑ(˜bW)). However, two missing neutrinos in the final state do not allow any direct probe of the T˜-odd WWH couplings (ℑ(bW), ℜ(˜bW)).We find that use of transverse polarization of the beams is essential to construct independent probes of the two anomalous ZZH couplings, which are even under CP and T˜transformations, viz.ΔaZand ℜ(bZ).We observed that there will be no significant gain 500 GeV), but with polarized beams is preferable from the point of view of studying anomalous V V H coupling. (For mathematical equations pl see the pdf file.)

Quantum Chromodynamics (QCD) is believed to be the theory of strong interactions. At high energies, it has been successfully applied to explain the interactions in accelerators. At these energies, the method used to do the calculations is perturbation theory. But at low energies, since the strong coupling constant becomes large, perturbation theory is no longer applicable. Hence, one needs non-perturbative approaches. Some of these approaches are based on the fundamental QCD Lagrangian, such as the QCD sum rules or lattice calculations. Some others use an effective theory approach to relate experimental observables one to the other. Chiral Perturbation Theory (ChPT) is one of these approaches. In this thesis, we make a review of chiral perturbation theory and its applications to study the mixing phenomenon between the neutral pseudoscalar mesons eta and eta-prime.

This thesis describes an analysis of the process e⁺e^— → l⁺l^- (where l = e, μ,, τ) at centre-of-mass energies between 88 GeV and 94 GeV, using the data collected by the DELPHI detector between the years 1991 and 1993. The leptonic decays of the Z° boson are selected without attempting to separate the three lepton types, thus making it an inclusive lepton analysis. The theory behind lepton pair production is introduced and the extraction of various electroweak parameters from the experimental observables is discussed. The LEP collider and the DELPHI detector are described, with special emphasis being given to the sub-detectors used in the analysis. The criteria used to select a high purity leptonic sample are described along with calculations of various backgrounds and efficiencies. The sample of selected leptonic events is then used to measure the cross-sections and forward-backward asymmetries. Finally, a fit to these cross-sections and asymmetries, together with the hadronic (e⁺e^- → qq̄) cross-sections, is carried out. Various Z° parameters are obtained: the mass and total width Mz-91.1876 ± 0.0052 GeV/c², Γ_z = 2.4971 ± 0.0061 GeV, the ratio of the hadronic to leptonic partial widths R_l = 20.73 ± 0.09, and the pole leptonic asymmetry (A°_FB)¹ = 0.0195 ± 0.0042. Using these results and the value of the strong coupling constant (α_s), determined by the DELPHI collaboration, the number of light neutrino species is determined to be N_ν = 3.045 ± 0.035. The leptonic partial width is found to be: Γ_l = 83.82 ± 0.29 MeV. Using the measured leptonic forward-backward asymmetries, the squared vector and axial-vector couplings of the Z° to charged leptons are found to be (ĝ_v¹)^{2</sup = (1.65 ± 0.36) x 10^-3 and (ĝ_a¹)}2</sup> = 0.2505 ± 0.0009. These values can be used to determine the effective rho parameter and the effective weak mixing angle: p̂ = 1.0020 ± 0.0036, and sin² θ^eff_lept = 0.2297 ± 0.0024. A full Standard Model fit to the data gives the values of the strong coupling constant, α_s, and the mass of the top quark, m_top, as being: α_s = 0.123 ± 0.010, m_top = 178⁺²²_-25 (expt)<sup>+18<sup>_-16(Higg s)GeV/c², where 60 < m_Higgs (GeV/c²) < 1000 with a central value of 300 GeV/c². All the results obtained agree with the results from the lepton-identified analyses (analyses in which leptonic events are selected on the basis of their individual flavour) and with the predictions of the Standard Model.

The production of three gauge bosons in high-energy collisions - in particular in view of a next-linear collider with center of mass energies in the TeV range - offers an unique opportunity to probe the Standard Model (SM) of today's particle physics. In this thesis we pay particular attention to the electroweak sector of the theory. We investigate the gauge structure {i. e. possible deviations from the SM predictions of gauge boson self-interactions manifest e. g. in anomalous quartic gauge boson couplings and Radiation zeros) as well as electroweak radiative corrections in order to improve theoretical predictions for SM processes. Quartic gauge boson couplings can be regarded as a direct window on the sector of electroweak symmetry breaking. We have studied the impact of three such anomalous couplings on the processes e+e(^-) → WWγ, ZZγ and Zγγ at LEP2 and a future linear collider. In certain high-energy scattering processes involving charged particles and the emission of one or more photons, the scattering amplitude vanishes for particular configurations of the final state particles. The fact that gauge symmetry is a vital ingredient for the cancellation to occur means that radiation zeros can be used to probe physics beyond the standard model. For example anomalous electroweak gauge boson couplings destroy the delicate cancellation necessary for the zero to occur. We have studied the process qq → WWγ. To match the expected experimental precision at future linear colliders, improved theoretical predictions beyond next-to-leading order are required. By choosing an appropriate gauge, we have developed a formalism to calculate such corrections for arbitrary electroweak processes. As an example we consider here the processes e(^+)e → f f and e(^+)e(^-) → W(^+)(_T)W(^-)(_T), W(^+)(_L)W(^-)(_L) and study the perturbative structure of the electroweak Sudakov logarithms by means of an explicit two-loop calculation. In this way we investigate how the Standard Model, with its mass gap between the photon and Z boson in the neutral sector, compares to unbroken theories like QED and QCD. We observe that the two-loop corrections are consistent with an exponentiation of the one-loop corrections. In this sense the Standard Model behaves like an unbroken theory at high energies.

The inter-dimensional system of a three-dimensional bulk and a two-dimensional interface is analyzed for bosons with quasirelativistic dispersion relation. Using the energy-dependent Green's function, the inter-dimensional quasirelativistic density of states inside the interface is solved analytically. We find that in the low-energy limit the inter-dimensional quasirelativistic density of states shows three-dimensional behaviour, while in the high-energy limit the density of states shows two-dimensional behaviour. This work is the first step in a process that will lead to a fully-analytical model for fermions in topological materials.

Thesis (Ph.D.)--McMaster University, 2004. / Supervisor: R.K. Bhaduri. Includes bibliographical references (p. 127-133). Also available via World Wide Web.