Littérature scientifique sur le sujet « EW Bosons »

Motivated by the μ-problem and the axion solution to the strong CP-problem, we extend the MSSM with one more chiral singlet field X ew . The underlying PQ-symmetry allows only one more renormalizable term X ew Hu Hd in the superpotential. The spectrum of the Higgs system includes a light pseudoscalar aX (in addition to the standard CP-even Higgs boson), predominantly decaying to two photons: aX →γγ. Both Higgs bosons might be in the range accessible to current LHC experiments.

We review the present bounds on Kaluza–Klein (KK)-excitations of Standard Model gauge bosons, predicted by TeV size extra dimensions, which have been set by the ElectroWeak Precision Test (EWPT) and recently by the direct searches performed at the CERN Large Hadron Collider (LHC). Concerning the theoretical framework we present results for the Non-Universal Extra Dimension (NUED) model with matter localized at the boundaries and all gauge bosons propagating into the bulk and acquiring KK-excitations. We also discuss its simplified version, NUED(EW), where only the ElectroWeak SM gauge bosons are allowed to propagate in the extra dimension, and its next-to-minimal version ElectroWeak Universal Extra Dimension (UED)(EW) where SU(3) is localized on the brane while the SU(2)×U(1) particle content fully propagates into the bulk.

The Higgs mechanism for imparting masses to gauge bosons and matter particles is obviated by showing that Yang–Mills gauge bosons have intrinsic nonzero masses (rest-frame energies) from self-interactions. Electroweak (EW) mixing is ruled out because it produces a photon field that is massive, carries EW charge, and does not satisfy Maxwell's equations. Other fundamental difficulties of the Standard Model are identified. A new gauge theory of electromagnetic, weak and strong interactions is derived from the Dirac equation with no other postulates and no free parameters. The three forces are intrinsically unified, the photon field is Maxwellian, weak interactions derive from spin (not isospin), and the weak and strong bosons are naturally massive and chiral. Charge is naturally quantized to integral values. Three generations of lepton pairs and elementary-hadron pairs, all with integral charges, are predicted, contradicting the phenomenology of fractional quark charges, but in full accord with experimental data on weak and strong processes and composite hadrons. Neutrinos are massive. The Dirac masses, the fine structure constant, neutrino oscillations and Cabibbo mixing are shown to have a common origin in the gravitational field. The new theory leads to a new interpretation of "negative energies" with cosmological implications. Finally, it is shown that key expressions of the EW formalism agree with those of the new theory and with experiments only if the mixing angle θ is given by sin 2 θ = 0.25, which accounts for the EW model's successes.

Four-dimensional Higgs field is identified with the extra-dimensional component of gauge potentials in the gauge-Higgs unification scenario. [Formula: see text] gauge-Higgs EW unification in the Randall–Sundrum warped space is successful at low energies. The Higgs field appears as an Aharonov–Bohm phase [Formula: see text] in the fifth dimension. Its mass is generated at the quantum level and is finite. The model yields almost the same phenomenology as the standard model for [Formula: see text], and predicts [Formula: see text] bosons around 6–10 TeV with very broad widths. The scenario is generalized to [Formula: see text] gauge-Higgs grand unification. Fermions are introduced in the spinor and vector representations of [Formula: see text]. Proton decay is naturally forbidden.

In this talk we describe examples of renormalizable strongly interacting field theories where chiral symmetry, broken at the UV cutoff by the presence of some irrelevant d > 4 operators in the fundamental Lagrangian, is recovered at low energy owing to the tuning of certain Lagrangian parameters. The interference of UV effects with IR features coming from the spontaneous breaking of the recovered chiral symmetry yields non perturbatively generated elementary fermion masses parametrically expressed by formulae of the kind mq ~ Cq(α)ΛRGI with α the gauge coupling constant and ΛRGI the RGI scale of the theory. Upon introducing EW interactions, this mechanism can be extended to give mass to EW bosons and leptons and can thus be used as an alternative to the Higgs scenario. In order to give the top quark and the weak gauge bosons a mass of the phenomenologically correct order of magnitude, the model must necessarily include (yet unobserved) super-strongly interacting massive fermions endowed, besides ordinary Standard Model interactions, with super-strong interactions with a RGI scale, ΛT ΛQCD in the few TeV range. Though limited in its scope (here we ignore hypercharge and leptons and discuss only the case of one family neglecting weak isospin splitting), the model opens the way to a solution of the naturalness problem and an understanding of the fermion mass hierarchy.

We extend our previous work on the precision electroweak tests in the Sp (6)L× U (1)Y family model to include for the first time the important [Formula: see text] vertex corrections encoded in a new variable ∊b, utilizing all the latest LEP data. We include in our analysis the one-loop EW radiative corrections due to the new bosons in terms of ∊1,b and ΔΓZ. We find that the correlation between ∊1 and ∊b makes the combined constraint much stronger than the individual ones. The model is consistent with the recent CDF result of [Formula: see text] but it; cannot accommodate mt≳195 GeV .

Assuming the Multiple Point Principle (MPP) as a new law of Nature, we considered the existence of the two degenerate vacua of the Universe: (a) the first Electroweak (EW) vacuum at v 1 ≈ 246 GeV—“true vacuum”, and (b) the second Planck scale “false vacuum” at v 2 ∼ 10 18 GeV. In these vacua, we investigated different topological defects. The main aim of the paper is an investigation of the black-hole-hedgehogs configurations as defects of the false vacuum. In the framework of the f ( R ) gravity, described by the Gravi-Weak unification model, we considered a black-hole solution, which corresponds to a “hedgehog”—global monopole, that has been “swallowed” by the black-hole with mass core M B H ∼ 10 18 GeV and radius δ ∼ 10 − 21 GeV − 1 . Considering the results of the hedgehog lattice theory in the framework of the S U ( 2 ) Yang-Mills gauge-invariant theory with hedgehogs in the Wilson loops, we have used the critical value of temperature for the hedgehogs’ confinement phase ( T c ∼ 10 18 GeV). This result gave us the possibility to conclude that the SM shows a new physics (with contributions of the S U ( 2 ) -triplet Higgs bosons) at the scale ∼10 TeV. This theory predicts the stability of the EW-vacuum and the accuracy of the MPP.

In the present paper, assuming the Multiple Point Principle (MPP) as a new law of Nature, we considered the existence of the two degenerate vacua of the Universe: the first Electroweak (EW) vacuum at [Formula: see text][Formula: see text]GeV — “true vacuum”, and the second Planck scale “false vacuum” at [Formula: see text] GeV. In these vacua, we investigated different topological defects. The main aim of this paper is an investigation of the black-hole-hedgehogs configurations as defects of the false vacuum. In the framework of the [Formula: see text] gravity, described by the Gravi-Weak unification model, we considered a black-hole solution, which corresponds to a “hedgehog” — global monopole, that has been “swallowed” by the black-hole with mass core [Formula: see text][Formula: see text]GeV and radius [Formula: see text][Formula: see text]GeV[Formula: see text]. Considering the results of the hedgehog lattice theory in the framework of the [Formula: see text] Yang–Mills gauge-invariant theory with hedgehogs in the Wilson loops, we have used the critical value of temperature for the hedgehogs confinement phase ([Formula: see text][Formula: see text]GeV). This result gave us the possibility to conclude that the SM shows a new physics with contributions of the [Formula: see text]-triplet Higgs bosons at the scale [Formula: see text][Formula: see text]TeV. Theory predicts the stability of the EW-vacuum and the accuracy of the MPP.

Based on recent perturbative and non-perturbative lattice calculations with almost quark flavors and the thermal contributions from photons, neutrinos, leptons, electroweak particles, and scalar Higgs bosons, various thermodynamic quantities, at vanishing net-baryon densities, such as pressure, energy density, bulk viscosity, relaxation time, and temperature have been calculated up to the TeV-scale, i.e., covering hadron, QGP, and electroweak (EW) phases in the early Universe. This remarkable progress motivated the present study to determine the possible influence of the bulk viscosity in the early Universe and to understand how this would vary from epoch to epoch. We have taken into consideration first- (Eckart) and second-order (Israel–Stewart) theories for the relativistic cosmic fluid and integrated viscous equations of state in Friedmann equations. Nonlinear nonhomogeneous differential equations are obtained as analytical solutions. For Israel–Stewart, the differential equations are very sophisticated to be solved. They are outlined here as road-maps for future studies. For Eckart theory, the only possible solution is the functionality, H(a(t)), where H(t) is the Hubble parameter and a(t) is the scale factor, but none of them so far could to be directly expressed in terms of either proper or cosmic time t. For Eckart-type viscous background, especially at finite cosmological constant, non-singular H(t) and a(t) are obtained, where H(t) diverges for QCD/EW and asymptotic EoS. For non-viscous background, the dependence of H(a(t)) is monotonic. The same conclusion can be drawn for an ideal EoS. We also conclude that the rate of decreasing H(a(t)) with increasing a(t) varies from epoch to epoch, at vanishing and finite cosmological constant. These results obviously help in improving our understanding of the nucleosynthesis and the cosmological large-scale structure.

The recently reported CDF excess at 120–160 GeV in invariant mass distribution of jet pairs accompanying W-boson1 is tentatively interpreted as a bound state of two W decaying to quark–antiquark pair. Nonperturbative effects of EW interaction obtained by application of Bogoliubov compensation approach lead to such bound state due to existence of anomalous three-boson gauge-invariant effective interaction. The application of this scheme gives satisfactory agreement with existing data without any adjusting parameter but the bound state mass 145 GeV.

La these porte sur les corrections mixtes QCD-EW au niveau NNLO a la productionDrell-Yan de bosons Z et W. Le processus Drell-Yan est un processus fondamentalpermettant de tester avec precision le Modele Standard (MS) de physique des partic-ules au sein de collisionneurs hadroniques, car ce dernier presente une section ecaceimportante, une signature experimentale tres propre, ainsi qu'une tres haute sensi-bilite aux proprietes des bosons de jauge. Pour toutes ces raisons, une prediction theorique precise et able, siginant ici que l'on garde sous contr^ole lestermes provenant des corrections perturbatives d'ordre superieur de la section ecaceet des distributions du mecanisme de production de Drell-Yan, est exigee pour menera bien des etudes de physique au niveau de collisionneurs hadroniques.Dans cette thèse , nous étudions les corrections QCD mixtes - EW à Drell - Yan traite à la NNLO . D'un point de vue technique , le calcul d'un tel ensemble de corrections impliquerait le cal-tion de diagrammes de Feynman très compliquées , La plus grande contribution provient des diagrammes dans lesquels la particule de décomposition ( Z ou boson W ) est presque sur - coquille.En utilisant les règles Cutkosky , nous pouvons ré-écrire l'intégration sur l'espace de phase de latermes d'interférence ( une boucle 2 à 2 diagrammes interféré avec le niveau arbre 2 à 2 etarbre 2 ou 3 diagrammes carré ) en termes de combinaison des intégrales de propagationteurs ayant la prescription et propagateurs de causalité droite avec une face .Ces intégrales peuvent être traités de la même manière que les corrections virtuelles . Cette réduction se fait en utilisant l' algorithme Laporta \ " , sur la base del'intégration par parties identités . Le calcul de l' IM est réalisée en utilisant la méthode de la différenceéquations. En conséquence , nous obtenons l' IM exprimée en série de Laurent ,où D est la dimension de l'espace - temps , la multiplication d'un facteur qui prend entenir compte de la limite souple de l'intégrale en D dimensions
The thesis concerns the NNLO mixed QCD-EW corrections to the Drell-Yan (DY)production of Z andW bosons, via the following reactions: pp(p) Z+X to l + Xand pp to W + X to l + X. This is a fundamental process for an accurate testof the Standard Model (SM) at hadron colliders, since it has a large cross section, aclean experimental signature. In particular, the Drell-Yan production of Ws is important for an accuratedetermination (via transverse mass and pT distributions) of the W mass, mW, aninput parameter of the model. Because of all these reasons, an accurate and reliable theoretical prediction forthe cross section and the distributions of the Drell-Yan production mechanism, thatmeans control on the higher-order perturbative corrections, is demanded for physicsstudies at hadron colliders. In this thesis, we study the mixed QCD-EW corrections to Drell-Yan processes at the NNLO. From a technical point of view, the calculation of such a set of corrections would involve the calcu-lation of very complicated Feynman diagrams, The biggest contribution comes from the diagrams in which the decaying particle(Z or W boson) is nearly on-shell. Using the Cutkosky rules, we can re-write the integration over the phase-space of theinterference terms (one-loop 2 to 2 diagrams interfered with the tree-level 2 to 2 andtree 2 to 3 diagrams squared) in terms of a combination of integrals with propaga-tors having the right causality prescription and propagators with the opposite one.These integrals can be treated in the same way as the virtual corrections. This reduction is done using the \Laporta Algorithm", based onthe Integration-by-Parts Identities. The calculation of the MIs is performed using the method of differentialequations. As a result, we get the MIs expressed as a Laurent series ,where D is the dimension of the space-time, multiplying a factor which takes intoaccount the soft limit of the integral in D dimensions

In questo lavoro presento le implementazioni di due processi di produzione di una coppia di bosoni elettrodeboli (EW) dallo scattering di due adroni in due diversi generatori di eventi Monte Carlo all'ordine next-to-next-to-leading (NNLO) nella cromodinamica quantistica (QCD) combinati con la parton shower (PS). Nella prima parte della tesi discuto l'implementazione del processo di produzione di due coppie di leptoni privi di massa con lo stesso sapore e carica opposta dallo scattering protone-protone all'interno del generatore di eventi Monte Carlo Geneva. Dopo aver brevemente introdotto il metodo Geneva, fornisco una descrizione dettagliata di due delle sue funzioni recentemente implementate. Dopo aver passato gli eventi attraverso la parton shower di Pythia8, mostro infine diverse distribuzioni di interesse fenomenologico e le confronto con i dati degli esperimenti ATLAS e CMS al Large Hadron Collider (LHC). Il generatore di eventi Geneva consente di abbinare il calcolo NNLO con la resummazione all'ordine logaritmico next-to-next-to-leading primo (NNLL') della zero-jettiness e quella all'ordine logaritmico next-to-leading (NLL) della one-jettiness. Poiché il contributo della risommazione è differenziale nel solo parametro della N-jettiness, può essere utilizzato per generare eventi soltanto dopo aver fornito la sua dipendenza dall'intero spazio delle fasi di radiazione. Le funzioni utilizzate a questo scopo sono dette funzioni di splitting e devono essere normalizzate in modo da non compromettere l'accuratezza della risommazione. In questo lavoro presento un modo per normalizzarle on the fly, che fornisce una migliore stabilità all'integrazione Monte Carlo. Tuttavia, tale metodo richiede il calcolo analitico di diversi limiti dello spazio delle fasi che dipendono dalle mappe utilizzate per proiettare le configurazioni con N+1 partoni di stato finale su quelle con N partoni di stato finale. Dopo aver descritto tutte le proiezioni attualmente disponibili in Geneva, presento un calcolo dettagliato della normalizzazione delle corrispondenti funzioni di splitting. Successivamente discuto la sottrazione all'ordine next-to-leading (NLO) delle singolarità infrarosse di QCD per qualsiasi processo di produzione di un singoletto di colore. Poiché Geneva richiede l'integrazione Monte Carlo on-the-fly delle ampiezze reali sottratte, mostro un modo per ottimizzare l'efficienza dell'integrazione che può essere particolarmente utile per i processi in cui il calcolo degli elementi di matrice reali è computazionalmente impegnativa. Nella seconda parte della tesi discuto l'implementazione del processo di produzione di una coppia di fotoni da uno scattering protone-protone all'interno del generatore di eventi Monte Carlo Powheg Box + MiNNLOPS. Tale processo richiede un trattamento dedicato poiché è afflitto da divergenze di elettrodinamica quantistica (QED) nel limite in cui qualsiasi fotone diventa collineare a un quark. Dopo aver brevemente introdotto il generatore di eventi Powheg Box e il metodo MiNNLOPS, presento gli strumenti appositamente creati per questo calcolo. Comincio descrivendo una tecnica generale per trattare qualsiasi processo con una sezione d'urto Born divergente nel generatore di eventi Powheg Box senza applicare alcun taglio a livello di generazione. Presento quindi una mappa che impedisce che le configurazioni finite dal punto di vista della QED con un partone di stato finale siano proiettate su configurazioni singolari senza partoni di stato finale. Infine discuto alcune modifiche alla versione originale del metodo MiNNLOPS volte a ridurre l'impatto dei contributi spuri oltre il NNLO. Dopo aver passato gli eventi attraverso la parton shower di Pythia8, concludo mostrando diverse distribuzioni di interesse fenomenologico e confrontandole con i dati di LHC più recenti dall'esperimento ATLAS.
In this work, I present the implementations of two processes of electroweak (EW) boson pair production from hadronic scattering within two different Monte Carlo event generators at next-to-next-to-leading order (NNLO) in quantum chromodynamics (QCD) combined with parton showers (PS). In the first part of the work, I discuss the implementation of the process of production of two same-flavor opposite-charge pairs of massless leptons from proton-proton scattering within the Geneva Monte Carlo event generator. After briefly introducing the Geneva method, I provide a detailed description of two of its newly-implemented features. After passing the events through the Pythia8 parton shower, I finally show several distributions of phenomenological interest and compare them with the data from the ATLAS and CMS experiments at the Large Hadron Collider (LHC). The Geneva event generator provides a framework for matching the NNLO calculation with the next-to-next-to-leading logarithmic prime (NNLL') resummation of the zero-jettiness and next-to-leading logarithmic (NLL) resummation of the one-jettiness. Since the contribution from the resummation is only differential in the N-jettiness parameter, it can be used for generating events only after providing its dependence on the full radiation phase space. The functions used for this purpose are called splitting functions and must be normalized so as not to spoil the accuracy of the resummation. In this work, I present a way of normalizing them on the fly, which provides better stability to the Monte Carlo integration. However, such a method requires the analytic computation of several phase-space boundaries, which depend on the mappings used for projecting the configurations with N+1 final-state partons onto those with N final-state partons. After describing all the mappings currently available in Geneva, I present a detailed calculation of the normalization of the corresponding splitting functions. I then discuss the next-to-leading order (NLO) subtraction of the infrared QCD singularities for any process of production of a color singlet. Since Geneva requires the on-the-fly Monte Carlo integration of the subtracted real amplitudes, I show a way to optimize the efficiency of the integration, which can be particularly useful for processes where the evaluation of the real matrix elements is computationally demanding. In the second part of the work, I discuss the implementation of the process of production of a photon pair from a proton-proton scattering within the Powheg Box + MiNNLOPS Monte Carlo event generator. Such a process requires a dedicated treatment since it is plagued by quantum electrodynamics (QED) divergences in the limit where any photons become collinear to a quark. After briefly introducing the Powheg Box event generator and the MiNNLOPS method, I present the dedicated tools devised for this calculation. I begin by describing a generic way to deal with any process with a divergent Born cross section in the Powheg Box event generator without applying any generation-level cuts. I then present a mapping that prevents QED-finite configurations with one final-state parton from being projected to singular configurations with no final-state partons. Finally, I discuss several modifications to the original version of the MiNNLOPS method aimed at reducing the size of spurious contributions beyond NNLO. After passing the events through the Pythia8 parton shower, I conclude by showing several distributions of phenomenological interest and comparing them with the most recent LHC data from the ATLAS experiment.

AbstractIn this chapter, we summarize the structure of the standard EW theory and specify the couplings of the intermediate vector bosons W±, Z and of the Higgs particle with the fermions and among themselves, as dictated by the gauge symmetry plus the observed matter content and the requirement of renormalizability