Academic literature on the topic 'Higgs Sector'

The Higgs sector of supersymmetric models with an additional SU (2)× U (1)Y singlet or an additional pair of Higgs doublet superfields is investigated. It is shown that in the model with a Higgs singlet bounds on Higgs boson masses are considerably weaker than in the minimal supersymmetric model; in particular, all neutral scalars can be heavier than about 150 GeV or lighter than [Formula: see text], whereas the mass of the charged Higgs boson is essentially unconstrained. The four doublet model resembles the minimal model more closely; in particular, the bounds for the heaviest and lightest neutral scalar and the heaviest charged Higgs boson are unaltered. In this model, many relations between masses of different Higgs bosons can be found; 44 of the 66 possible decays of one Higgs boson into another Higgs boson plus a real W or Z boson are kinematically forbidden. It is also shown that in both models, the lightest neutral scalar becomes indistinguishable from the standard model Higgs boson if all other Higgs bosons of the model are much heavier than Mw.

While the existence of a Higgs boson with a mass near 125 GeV has been clearly established, the detailed structure of the entire Higgs sector is yet unclear. Besides the Standard Model interpretation, various possibilities for extended Higgs sectors are being considered. The minimal supersymmetric extension (MSSM) features two Higgs doublets resulting in five physical Higgs bosons, which are subject to direct searches. Alternatively, more generic Two-Higgs Doublet models (2HDM) are used for the interpretation of results. The Next-to-Minimal Supersymmetric Model (NMSSM) has a more complex Higgs sector with seven physical states. Also exotic Higgs bosons decaying to invisible final states are considered. This article summarizes recent findings based on results from collider experiments.

While the existence of a Higgs boson with a mass near 125 GeV has been clearly established, the detailed structure of the entire Higgs sector is yet unclear. Besides the Standard Model interpretation, various possibilities for extended Higgs sectors are being considered. The minimal supersymmetric extension (MSSM) features two Higgs doublets resulting in five physical Higgs bosons, which are subject to direct searches. Alternatively, more generic Two-Higgs Doublet models (2HDM) are used for the interpretation of results. The Next-to-Minimal Supersymmetric Model (NMSSM) has a more complex Higgs sector with seven physical states. Also exotic Higgs bosons decaying to invisible final states are considered. This article summarizes recent findings based on results from collider experiments.

One doublet of complex scalar fields is the minimal content of the Higgs sector in order to achieve spontaneous electroweak symmetry breaking and, in turn, to generate the masses of fundamental particles in the Standard Model. However, several theories beyond the Standard Model predict a nonminimal Higgs sector and introduce additional singlets, doublets or even higher-order weak isospin representations, thereby yielding additional Higgs bosons. With its high proton–proton collision energy (13 TeV during Run-2), the Large Hadron Collider opens a new window towards the exploration of extended Higgs sectors. This review article summarises the current state-of-the-art experimental results recently obtained in searches for new neutral and charged Higgs bosons with a partial or full Run-2 dataset.

We examine the allowed mass range of the charged Higgs field H+ in a minimal left-right symmetric model. We find that the mass of this Higgs is nearly degenerate with the mass of the flavor-changing neutral Higgs, and this implies MH+≳5~10 TeV. We examine a number of solutions, but fail to evade this restriction. If this constraint can not be avoided, the H+ (and very likely all other left-right extended Higgs particles) would be virtually undetectable at all experimental facilities, including the SSC.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 67-75).
In this thesis, we are investigating cosmological implications of hidden sector models which involve scalar fields that do not interact with the Standard Model gauge interactions, but couple directly to the Higgs field. We particularly focus on their relic particle density as a candidate for dark matter. For the case of hidden sector without a gauge field we have improved the accuracy of the bounds on the coupling constant and give bounds on the Lagrangian parameters. Models with Abelian and non-Abelian gauge fields are also studied with relic density bounds, BBN and galactic dynamics constraints. Several discussions on phase transitions and alternative dark matter candidates are included.
by Serkan Cabi.
Ph.D.

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.

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.

After reviewing the reasons to believe that the road to shed light to Beyond Standard Model physics pass through a better understanding of the Higgs sector, we outline two complementary approaches along this main line: either tackling the phenomenological challenge to extract as much information as possible from collider experiments, or undertaking a theoretical investigation of new physics scenarios in order to gain knowledge on possible explanations to the Higgs mysteries. In the first part of the dissertation, we adopt a phenomenological approach and discuss the general problem of including infrared Standard-Model-like corrections in a model-independent new physics characterisation of Higgs decay and production processes. We deal first with infrared electromagnetic corrections (bremsstrahlung), providing a compact formalism to generally describe fermion bremsstrahlung in leading logarithmic approximation and then exemplifying its effectiveness through the “h -> 2e 2mu” case study. Subsequently we switch to a discussion of double-logarithmic mass singularities stemming from the electroweak sector, which affects among the others also Higgs production processes in the high-energy regime. We provide here a detailed analysis of such mass singularities in generic new physics scenarios for the case study of Higgsstrahlung. In the second part of the dissertation, we adopt a complementary approach and perform a theoretical study of high-scale supersymmetry. We exploit the highly constrained structure of the Higgs sector in such theories, together with other of their important features such as gauge coupling unification and radiative breaking of electroweak symmetry, to draw intriguing conclusions regarding the viability of such theories in the plane of Higgs and top-quark masses.
Per svelare i misteri della fisica oltre il Modello Standard si deve innanzitutto capire appieno il Modello Standard stesso ed in particolare il settore di Higgs, di gran lunga il meno compreso. In questa dissertazione delineiamo due possibili approcci a tale riguardo: si può assumere un’atteggiamento fenomenologico, cercando di parametrizzare in maniera ottimale gli esperimenti ad LHC, oppure un punto di vista più formale cercando di aumentare la nostra comprensione teorica del settore di Higgs (nella speranza di comprenderne i misteri). Nella prima parte di questa dissertazione, affrontiamo la questione delle correzioni infrarosse nella fisica degli acceleratori di particelle. Il nostro obiettivo è una descrizione generale di tali correzioni, da poter utilizzare in modo “model-independent” quando si cerca di caratterizzare la fenomenologia di nuova fisica ad LHC. Innanzitutto ci focalizziamo sulle correzioni elettromagnetiche (bremsstrahlung), fornendo un formalismo compatto e generale per descrivere la bremsstrahlung da correnti fermioniche neutre. Esemplifichiamo poi i nostri risultati tramite l’esempio del decadimento “h -> 2e 2mu”. In seguito ampliamo la nostra discussione per includere le correzioni elettrodeboli, limitandoci ai cosiddetti contributi doppio-logaritmici (importanti per i processi di produzione dell’Higgs) e concentrandoci sul caso di produzione associata Higgs-Z e Higgs-W. Nella seconda parte di questa dissertazione adottiamo un approccio complementare e effettuiamo uno studio teorico di una classe di teorie supersimmetriche chiamate “high-scale SUSY”. Sfruttando la struttura estremamente rigida del settore di Higgs in tali teorie, traiamo conclusioni molto interessanti riguardo la loro fattibilità nel piano (“massa dell’Higgs”, “massa del top”).

Complete one-loop results for the decay widths of neutral Higgs bosons ( h(_a)) into lighter neutral Higgs bosons ( h(_b), h(_c). ) arc presented for the MSSM with complex parameters. The results are obtained in the Feynman-diagrammatic approach, taking into account the full dependence on the spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. The genuine triple-Higgs vertex contributions are supplemented with two-loop propagator-type corrections, yielding the currently most precise prediction for this class of processes. The genuine vertex corrections turn out to be very important, yielding a large increase of the decay width compared to a prediction based on the tree-level vertex. One-loop propagator-type mixing between neutral Higgs bosons and Goldstone and Z bosons is also consistently taken into account. Complete one-loop results for the decay of a neutral Higgs boson into fermions are also presented, which include the full dependence on complex phases. The new results are used to analyse the impact of the experimental limits from the LEP Higgs searches on the parameter space with a very light MSSM Higgs boson. It is found that a significant part of the parameter space of the CPX benchmark scenario exists where channels involving the decay h(_2)→ h(_1) h(_1) have the highest search sensitivity, and the existence of an unexcluded region with M(_h1) ~ 45 GeV is confirmed. The public code Higgs Bounds is also presented, which can be used in conjunction with models with an arbitrary number of neutral Higgs bosons to determine whether parameter points have been excluded at the 95% CL by the LEP and Tevatron Higgs searches.

Avec la découverte en juillet 2012 par les collaborations CMS et ATLAS d'un nouveau scalaire, aux propriétés similaires à celles d'un boson prédit plus de 50 ans auparavant, la phénoménologie au-delà du modèle standard (SM) a fait un grand pas. En effet, la découverte de cette pièce manquante du puzzle électrofaible a rendu certains modèles impossibles, tout en renforçant la crédibilité du SM. Cependant, on sait que le SM n'est pas le mot de la fin, car certaines de ses prédictions ne s'accordent pas avec les expériences, et ce boson est donc vu comme une porte vers de nouveaux secteurs de la physique. Après une introduction au SM et aux statistiques de la physique des particules, nous présenterons un paramétrage des couplages mesurés au LHC, afin de contraindre, via ces couplages, des modèles de physique au-delà du SM, plus fondamentaux. Ce paramétrage, s'intéressant particulièrement aux couplages à boucles, permettrait de lever une corrélation existant entre les paramètres actuellement utilisés. Nous étudierons ensuite la possibilité d'existence d'un scalaire, plus léger que celui observé, et ayant échappé aux recherches passées, et de sa recherche au LHC à l'aide de ce paramétrage. Nous donnerons des exemples de paramètres faisant apparaître un tel scalaire, dans le 2HDM et le NMSSM. Enfin, nous verrons que le scalaire peut influencer la production d'une paire de bosons de jauge faible, et qu'à l'aide de notre paramétrage, l'analyse de ce processus peut être utilisée de manière cohérente avec les mesures au pic de masse pour contraindre ces couplages. Nous finirons avec quelques limites de cette approche, ainsi que des propositions d'améliorations
With the discovery of a new particle in July 2012 by the CMS and ATLAS experiments, with properties resembling those of a boson predicted about 50 years earlier by theorists, the search for physics outside of the standard model of particle physics (SM) has made a big step. Indeed, the existence of this piece of the electroweak symmetry breaking proved wrong many theories, while giving more credit to the SM. However, because of some observations it fails to match, we know the SM cannot be the final word, and it is hoped that the study of this new particle will be a path to new sectors of physics. After a brief description of the SM and of the statistics of particle physics, we will present a way to parametrise the couplings measured at CERN, in order to constrain, through these couplings, more fundamental models describing physics beyond the standard model. This parametrisation, focusing on loop-induced couplings, would allow to lift a correlation existing between parameters currently used by experimentalists. We will then study the feasibility of a search for another scalar, lighter than the one discovered and which would have escaped previous searches, through the use of the same parametrisation. In two models, the 2HDM and the NSSSM, values of parameters yet unconstrained are shown.Finally, we will see that this scalar can also influence the joint production of two weak gauge bosons. We will show that the analysis of this process can be used in a coherent manner with on-shell Higgs measurements to constrain its couplings through our parametrisation. We will then end with a brief look at some limitation of this approach, before suggesting ways to overcome them

The Standard Model (SM) of elementary particles, a model experimentally verified to an un-precedented level of accuracy, foresees the existence a scalar particle, the so-called Higgs boson, that breaks the electroweak symmetry and explains the non-null value of fermion masses. The pursue of the Higgs boson has been carried out by several experiments at the LEP II and Tevatron colliders in the past, but unsuccessfully. However, during the year 2011, the ATLAS and CMS experiments at LHC began to observe some evidence of the elusive particle, finally confirming the discovering in 2012. Even if the Higgs boson and its observed properties represent a triumph for the Standard Model, there are many unresolved phenomena that the SM cannot explain. Several extensions have been proposed; some of the most relevant foresee several Higgs bosons instead of only one. After the commissioning of the LHC collider in 2011 and the first evidences of a light scalar boson, one of the fundamental questions to be answered was whether the new particle was the SM Higgs boson, or the lightest among the bosons foreseen by the theories extending the SM. The confirmation could come from the measurements of the Higgs couplings to the SM particles, or alternatively from the observation of new production processes and decays not predicted by the SM, or measured at a different rate. The associated production with b quarks of a Higgs boson, and its decay into pairs of b quarks, is a process with a small predicted cross section in the SM, and its observation would imply the presence of new physics. Previous searches at the Tevatron collider reported a slight excess in this channel. Afterwards the discovery of the Higgs boson in July 2012 by the CMS and ATLAS experiments, the knowledge of the properties of the Higgs boson and its mass become a valuable handle to increase the sensitivity of new physics searches. One of the most beneficial channels is the search of a heavy pseudoscalar A, and its decay into a Z boson and a light Higgs boson h, the latter assumed to be the recently-discovered 125 GeV boson. The Z boson is sought in its decay into a pair of electrons or muons, and the Higgs into a pair of b quarks. This channel, not predicted by the SM, probes a region in the parameter phase-space of beyond the SM theories which is, to some extent, complementary to the one of the multi-b search.
Il modello standard (SM) delle particelle elementari, verificato sperimentalmente ad alta precisione, prevede l’esistenza di una particella scalare, il bosone di Higgs, grazie al quale avviene la rottura di simmetria elettrodebole ed è possibile spiegare le masse non nulle dei fermioni. La ricerca del bosone di Higgs è stata perseguita in passato da diversi esperimenti ai collisori LEP II e Tevatron, ma sempre con esito negativo. Solo nell’anno 2011, all’acceleratore LHC gli esperimenti ATLAS ed CMS hanno cominciato ad osservare le prime evidenze dell’elusiva particella, per poi confermane definitivamente la scoperta nel 2012. Tuttavia, pur essendo l’esistenza e le caratteristiche osservate del bosone di Higgs l’ennesima verifica sperimentale della validità del modello standard, esistono fenomeni naturali che esso non è in grado di spiegare, come ad esempio la massa dei neutrini o la materia oscura. Diverse estensioni del modello standard sono state proposte; diverse tra le più accreditate prevedono non uno, ma più bosoni. Con l’entrata a regime di LHC nel 2011 e le prime evidenze di un bosone di Higgs, una delle domande fondamentali a cui dare risposta era se il segnale che si stava osservando fosse dovuto al bosone di Higgs dello SM, oppure al più leggero dei diversi bosoni previsti dalle teorie oltre il modello standard. La risposta poteva venire sia dalla misura degli accoppiamenti dell’Higgs alle particelle dello SM, sia osservando processi e decadimenti non previsti dallo SM, o misurati con una frequenza maggiore dell’atteso. La produzione di un bosone di Higgs in associazione con quarks b, e il suo successivo decadimento in una coppia di quark b, è un processo difficilmente osservabile nel modello standard, pertanto la sua osservazione averebbe significato la presenza di nuova fisica. Precedenti ricerche a Tevatron hanno evidenziato un lieve eccesso in questo canale. In seguito alla scoperta del bosone di Higgs nel Luglio 2012 da parte degli esperimenti CMS e ATLAS, la conoscenza delle proprietà di questa particella, ivi compresa la sua massa, diventano informazioni che possono essere utilizzate per aumentare la sensibilità a ricerche di processi di nuova fisica. Uno dei canali che beneficia di questa informazione è la ricerca di un bosone pseudoscalare A, in particolare nel suo decadimento in un bosone Z e un bosone di Higgs leggero h, che si assume essere quello di massa 125 GeV recentemente scoperto. Lo stato finale consiste in una coppia di elettroni o muoni originati dal decadimento del bosone Z, e una coppia di quark b dal decadimento dell’Higgs. Questo canale, non previsto dallo SM, permette di sondare una regione dello spazio dei parametri di teorie oltre il modello standard per certi versi complementare a quella del canale con molti b nello stato finale.

AdS/CFT correspondence combines ideas of holography and duality in a way that allows one to make calculations in the otherwise hardly accessible (strongly coupled) regime of the target theory. In this thesis we are interested in describing strongly coupled sectors in the Standard Model and beyond within the holographic framework. In particular, we use the bottom-up holographic approach in application to the phenomenology of QCD and Composite Higgs. In the latter a new strong interaction binds hyper-fermions into composite states at TeV energies, and the Higgs is one of the pseudo-Goldstone bosons appearing as a result of new flavor symmetry breaking. In the bottom-up model building the conformal invariance of the AdS space must be broken by the manual introduction of the wall in the extra dimension. We favor the soft wall models, because they reproduce linear radial Regge-like spectra of the states. In application to QCD, we provide results on the determination of the QCD deconfinement temperature in the bottom-up models of different types, and the study of the low-energy QCD physics triggered by a novel implementation of the chiral symmetry breaking in the soft wall model. The phenomenological outcome of the latter model is given in terms of the fit to fifteen QCD observables with the RMS error of 30%. Concerning the New Physics, we specialize on the minimal Composite Higgs case. We calculate masses of the new composite resonances, estimate several couplings between the new sector states and the electro-weak bosons and analyse the holographic realization of the first and second Weinberg sum rules. Experimental limitations on the electro-weak precision observables and the misalignment angle, as well as the known value of the elctro-weak scale, constrain the parameter space of the holographic model and specify the scale of its predictions. We conclude that the model is able to accommodate new vector resonances with masses in the range 2 TeV to 3 TeV without encountering phenomenological difficulties.
En esta tesis estudiamos sectores fuertemente acoplados en el Modelo Estándar (SM) y más allá (BSM) dentro del enfoque holográfico. Nuestro propósito es sobresalir el método en la aplicación a la física mejor estudiada y luego utilizar el conocimiento acumulado en el ámbito que está fuera del alcance de los experimentos contemporáneos. Las ideas holográficas aparecieron después de que se hiciera la observación de Bekenstein y Hawking sobre la naturaleza de la entropía del agujero negro. El principio holográfico general se formuló de la siguiente manera: todo el contenido de información de una teoría de la gravedad cuántica en un volumen dado se puede codificar en una teoría eficaz sobre la frontera. La correspondencia anti-de Sitter / teoría conforme de campos (AdS/CFT) combinó holografía y dualidades (por esa razón también se conoce con el nombre de dualidad gauge/gravedad) en una interesante propuesta para la investigación de la teoría de cuerdas y los aspectos de la gravedad cuántica. Sin embargo, pronto se descubrió que la teoría supersimétrica $ N = 4 $ de Yang-Mills, por la que Maldacena ha encontrado un la teoría dual de cuerdas, es en cierto modo similar a la cromodinámica cuántica (QCD) en el régimen fuertemente acoplado. Eso desvió la atención a la parte gauge de la correspondencia. Sorprendentemente, la teoría de cuerdas es más fácil de resolver que la teoría mundana de quarks y gluones porque se conjetura que está en el límite semiclásico y débilmente acoplado. Existen pocas herramientas teóricas para estudiar regímenes fuertemente acoplados. Para QCD, el más conocido es la formulación lattice de primer principio. Reveló mucho sobre la naturaleza de QCD. Por ejemplo, señaló que la transición de desconfinamiento de los estados de hadrones ligados al plasma de quark-gluones ocurre como un cruce suave. Desafortunadamente, no es omnipotente: además de las restricciones tecnológicas y la complejidad cada vez mayor de los cálculos numéricos, existe, por ejemplo, un problema mucho más profundo relacionado con la inclusión del potencial químico de los quarks finito. Este último define uno de los ejes del diagrama de fase QCD, de modo que la lattice QCD no puede analizarlo en su totalidad. A su vez, la holografía se puede utilizar para abordar varios aspectos de QCD: espectros de mesón, glueball y barión, interacciones hadrónicas y el proceso de hadronización en colisionadores, confinamiento y ruptura de simetría quiral, materia hadrónica en condiciones externas extremas. Sin embargo, existen varias limitaciones en QCD que aparecen en construcciones similares a AdS/CFT. Primero, se supone que debe estar en el límite de $N_c$ grande. Independientemente de la holografía, se demostró que este límite puede verse como una versión exagerada de QCD tricolor común: el número de excitaciones radiales de un estado dado es infinito, cada una de ellas es infinitamente estrecha, el desconfinamiento representa una transición de fase real, etc. En segundo lugar, la propiedad de confinamiento no se puede combinar con CFT; uno debería encontrar una manera de romper la invariancia conforme e introducir una escala QCD $ \ Lambda_ {QCD} $. No hace falta decir que se desconoce la teoría dual de cadena exacta para QCD. En esta tesis utilizamos el llamado enfoque holográfico bottom-up (AdS / QCD) que fue desarrollado para superar las dificultades teóricas y que se centra en la descripción exitosa de la fenomenología QCD. En AdS / QCD se construyen modelos de cinco dimensiones siguiendo las reglas del diccionario AdS / CFT. Los campos 5D corresponden a los operadores de interpolación en 4D y pueden considerarse como la conexión entre la fuente sobre la frontera y un punto en el volumen. Las funciones de Green, que definen la teoría 4D, se pueden calcular a partir de la acción 5D debido a la correspondencia entre las funciones de partición. Al mismo tiempo, la representación de Kaluza-Klein de un campo 5D contiene los grados de libertad físicos reales 4D con los números cuánticos de los operadores duales. Se puede extraer el espectro de masas de estos modos. La invariancia conforme del espacio $ AdS_5 $ se rompe mediante la introducción manual de la pared en la quinta dirección ($ z $). Básicamente, se pueden considerar paredes de dos tipos: la pared dura, que es solo un corte a una distancia finita en la dirección $ z $, y la pared blanda, donde se introduce un perfil exponencial en la acción para suprimir cualquier contribución en $ z $ -infinito. Hay esfuerzos para aplicar la holografía en varios sistemas físicos, incluso tan desconectados de la teoría de cuerdas como la física de la materia condensada. Nuestro interés particular es la incorporación de modelos AdS / QCD en el ámbito de la física BSM. Hay varias ideas sobre cómo podrían producirse dinámicas fuertes allí. Nos centramos en los modelos de Higgs compuesto (CH), donde la nueva interacción fuerte une a los hiper-fermiones en estados compuestos a energías TeV, en paralelo a QCD que une quarks de SM en mesones y bariones. Este nuevo sector a la escala energética de varios TeV puede resolver el problema de naturalidad del SM al precio de una afinación relativamente pequeña. Además, proporciona predicciones BSM dentro del alcance experimental del futuro cercano. Por lo tanto, en esta tesis informamos sobre nuestras investigaciones de QCD y CH dentro del enfoque holográfico bottom-up. Una revisión de una amplia gama de temas es un requisito previo en este tipo de estudio que combina construcciones teóricas sofisticadas y análisis de datos fenomenológicos. En el Capítulo 2 revisamos el formalismo teórico detrás de las dualidades gauge/gravedad. Los capítulos 3 y 4 se refieren a las características teóricas y fenomenológicas relevantes de la QCD. En el Capítulo 5 presentamos modelos simples de AdS/QCD y delineamos el análisis holográfico de los espectros de partículas. El Capítulo 6 contiene nuestros resultados originales sobre la determinación de la temperatura de desconfinación de QCD en el marco de AdS/QCD. El Capítulo 7 corresponde al artículo dedicado al estudio de la física de QCD de baja energía desencadenada por la implementación particular de la ruptura de simetría quiral en el modelo con la pared blanda. En el Capítulo 8 se presenta un trabajo sobre Higgs compuesto holográfico. Comenzamos en el Capítulo 2 con una descripción del formalismo central, el de la correspondencia AdS / CFT. Las prescripciones holográficas generales se recopilan en el diccionario AdS / CFT. Luego, especificamos al caso la dualidad de Maldacena entre la teoría de cuerdas tipo IIB en $ AdS_5 \ times S_5 $ espacio-tiempo y la teoría supersimétrica $N=4$ de Yang-Mills en cuatro dimensiones. Discutimos en qué sentido la parte gauge de esta dualidad es similar a large- $ N_c $ QCD y qué aspectos faltan. En el Capítulo 3 discutimos algunos temas seleccionados de QCD. Revisamos varios métodos bien establecidos que permiten estudiar la QCD en diferentes regímenes: a gran número de colores, a pequeñas energías, centrándonos en las implicaciones de la simetría quiral y a temperatura finita. También cubrimos la expansión de productos del operador, la formulación lattice de QCD, sus predicciones e implicaciones. Los observables fenomenológicos de hadrones se consideran en el Capítulo 4 e incluyen los espectros de masas de resonancia, los acoplamientos y los factores de forma. Investigamos en detalle la idea de excitaciones de mesones radiales que pertenecen a las trayectorias radiales lineales de Regge, y enfatizamos la noción de trayectorias de mesones radiales universales. También se analizan los espectros de glueballs, estudiados sobre lattice. Habiendo resaltado las características fenomenológicas relevantes de QCD, pasamos a su implementación holográfica bottom-up. El formalismo general de incluir resonancias QCD en el volumen 5D se presenta en el Capítulo 5. Presentamos varios modelos simples de AdS/QCD: pared dura, pared blanda y pared blanda generalizada. Se evalúan sobre la base de su éxito en la descripción de los espectros fenomenológicos. Los modelos de paredes blandas demuestran la linealidad de las trayectorias radiales esperadas en las teorías con la realización adecuada del confinamiento. Además, mencionamos la posibilidad de adquirir familias de perfiles de paredes blandas que conduzcan a los mismos espectros. En AdS / QCD se asume que la transición de la fase de desconfinamiento es dual a la transición Hawking-Page entre diferentes geometrías en la teoría 5D. Eso nos permite estimar la temperatura (pseudo) crítica de desconfinamiento, $T_c$. En el Capítulo 6 exploramos varios modelos holográficos con diferentes opciones para fijar sus parámetros con el fin de obtener el valor fenomenológico de $T_c$. Los resultados dependen bastante de la elección de los parámetros del modelo. Concluimos que hay un subconjunto que proporciona $T_c$ cerca de las estimaciones de quenched lattice y grande-$ N_c $, y aquellas que predicen $ T_c $ en el rango físico (temperatura de freeze-out, estimaciones lattice con quarks dinámicos). El mecanismo holográfico AdS / QCD para la implementación dual de la ruptura de la simetría quiral se desarrolla en el Capítulo 7. Elegimos el marco de pared blanda e introducimos varias características novedosas para acomodar mejor los modos Goldstone. El modelo resultante no tiene muchos parámetros libres y debido a este minimalismo proporciona interesantes interrelaciones entre diferentes sectores. Se extraen varios observables de interés. El resultado fenomenológico se da en términos del ajuste a quince QCD observables con el error cuadrático medio de $ ~ 30%$. En el Capítulo 8 comenzamos con la motivación para la extensión de BSM con el sector fuertemente acoplado y enfatizamos las ventajas de los modelos CH. Además, nos especializamos en el caso de CH mínimo con el patrón de ruptura de la nueva simetría de sabor tipo $SO (5) -> SO (4) $. Allí aplicamos la técnica AdS / QCD y, en concreto, utilizamos la experiencia del capítulo anterior. Sin embargo, las diferencias con el caso QCD no son tan simples como el intercambio de los grupos de "sabor" y "color". La reconsideración de la realización holográfica y el papel de los bosones de Goldstone es un desarrollo importante del capítulo. Calculamos las masas de las nuevas resonancias compuestas, estimamos varios acoplamientos entre los nuevos estados del sector y los bosones electro-débiles y analizamos la realización holográfica de la primera y segunda reglas de suma de Weinberg. Las limitaciones experimentales de los observables de precisión electro-débil y el ángulo de desalineación, así como el valor conocido de la escala electro-débil, restringen el espacio de parámetros del modelo holográfico y especifican la escala de sus predicciones. Concluimos que el modelo es capaz de acomodar nuevas resonancias vectoriales con masas en el rango de 2-3 TeV sin encontrar dificultades fenomenológicas. En conclusión, aunque los métodos AdS / QCD están lejos de ser precisos, son útiles aunque solo sea para proporcionar un marco bastante simple donde se pueden diseñar y probar diferentes escenarios. Al mismo tiempo, es fundamental tratar conscientemente la cantidad de libertad que otorga este marco fenomenológico. Nos esforzamos por encontrar este equilibrio y elaboramos para motivar bien las suposiciones y elecciones tomadas a lo largo de la construcción del modelo holográfico.

The electroweak sector of the SM described by an SUL(2)UY(1) gauge symmetry which is broken spontaneously to Uem(1) is introduced. The generation of boson and fermion masses by the Higgs effect is discussed. The properties of the Higgs sector are examined. The conditions for decoupling and the hierarchy problem are discussed.

Before the LHC, there was the Tevatron, which ran at the high-energy frontier for approximately 25 years. Many of the modern analysis tools used at the LHC were first developed at the Tevatron. In this chapter, benchmark data analyses (and related theoretical tools), such as for W/Z bosons, photons, and jets, are described. The apex of the Tevatron was the discovery of the top quark. Measurements of the top quark cross section and of the top quark mass are examined and tt¯ asymmetry measurements and predictions are reviewed. Although attributed to many Beyond-the-Standard Model scenarios, the ultimate explanation for the larger than expected asymmetry turned out to be higher order QCD. There were very active Higgs boson searches at the Tevatron. Although the Tevatron was able to somewhat exclude the allowed Higgs mass range, time ran out before any observation could be made. This was left to the LHC.

At the core of any theoretical description of hadron collider physics is a fixed-order perturbative treatment of a hard scattering process. This chapter is devoted to a survey of fixed-order predictions for a wide range of Standard Model processes. These range from high cross-section processes such as jet production to much more elusive reactions, such as the production of Higgs bosons. Process by process, these sections illustrate how the techniques developed in Chapter 3 are applied to more complex final states and provide a summary of the fixed-order state-of-the-art. In each case, key theoretical predictions and ideas are identified that will be the subject of a detailed comparison with data in Chapters 8 and 9.

In this chapter we present the solution to the problem of mass. It is based on the phenomenon of spontaneous symmetry breaking (SSB). We first give the example of buckling, a typical example of spontaneous symmetry breaking in classical physics. We extract the main features of the phenomenon, namely the instability of the symmetric state and the degeneracy of the ground state. The associated concepts of the critical point and the order parameter are deduced. A more technical exposition is given in a separate section. Then we move to a quantum physics example, that of the Heisenberg ferromagnet. We formulate Goldstone’s theorem which associates a massless particle, the Goldstone boson, to the phenomenon of spontaneous symmetry breaking. In the last section we present the mechanism of Brout–Englert–Higgs (BEH). We show that spontaneous symmetry breaking in the presence of gauge interactions makes it possible for particles to become massive. The remnant of the mechanism is the appearance of a physical particle, the BEH boson, which we identify with the particle discovered at CERN.

AbstractThis chapter, Chaps. 10.1007/978-3-030-38207-0_3 and 10.1007/978-3-030-38207-0_4 present a self-contained introduction to the Standard Model of fundamental interactions, which describes in the unified framework of gauge quantum field theories all of the fundamental forces of nature but gravity: the strong, weak, and electromagnetic interactions. This set of chapters thus provides both an introduction to the Standard Model, and to quantum field theory at an intermediate level. The union of the three chapters can be taken as a masters’ level course reference, and it requires as a prerequisite an elementary knowledge of quantum field theory, at the level of many introductory textbooks, such as Vol. 1 of Aitchison-Hey, or, at a somewhat more advanced level, Maggiore. The treatment is subdivided into three parts, each corresponding to an individual chapter, with more advanced field theory topics introduced along the way as needed. Specifically, this chapter presents the general structure of the Standard Model, its field content, and symmetry structure. This involves an introduction to non-abelian gauge theories both at the classical and quantum level. Also, it involves a discussion of spontaneous symmetry breaking and the Higgs mechanism, that play a crucial role in the architecture of the Standard Model, and their interplay with the quantization of gauge theories. Chapter 10.1007/978-3-030-38207-0_3 then presents the electroweak sector of the Standard Model. This requires introducing the concepts of CP violation and mixing, and of radiative corrections. Finally, Chap. 10.1007/978-3-030-38207-0_4 presents the strong sector of the theory, which requires a more detailed treatment of renormalization and the renormalization group.

AbstractIn the first two Sections I recount few episodes that highlight the unique personality of Bruno Touschek, and I propose to call ‘Bruno’s domain’ the electron–positron energy range dominated by the one-photon channel. Section 8.3, devoted to a presentation of the four LEP detectors, is followed by three Sections describing electroweak precision tests, in particular those involving the production of b-quarks, Higgs searches and the most accurate measurements of the strong coupling. In Sects. 8.7 and 8.8, the unification of the forces is discussed from a personal point of view and the legacy of LEP to the LHC experiments is highlighted.