Academic literature on the topic 'Particle Physics - Standard Model (SM)'

We present new models of particle physics beyond the Standard Model. These models include extensions to the ideas of extra dimensions, deconstruction, supersymmetry, and Higgsless electroweak symmetry breaking. Besides introducing new models and discussing their consequences, we also discuss how galaxy cluster surveys can be used to constrain new physics beyond the Standard Model.;We find that an ultraviolet completion of gauge theories in the Randall-Sundrum model can be found in a deconstructed theory. The warping of the extra dimension is reproduced in the low energy theory by considering a general potential for the link fields with translational invariance broken only by boundary terms. The mass spectrum for the gauge and link fields is found to deviate from the Randall-Sundrum case after the first couple modes. By extending this model to a supersymmetric theory space, we find that supersymmetry is broken by the generation of a cosmological constant. Unless the theory is coupled to gravity or messenger fields, the spectrum remains supersymmetric.;We also present a hybrid Randall-Sundrum model in which an infinite slice of warped space is added to the extra dimension of the original theory. The hybrid model has a continuous gravitational spectrum with resonances at the Kaluza-Klein excitations of the original orbifolded model. A similar model is considered where the infinite space is cutoff by the addition of a negative tension brane. SU(2)L x SU(2)R x U(1)B-L gauge fields are added to the bulk of our hybrid model and we find that electroweak symmetry is broken with an appropriate choice of boundary conditions. By varying the size of the extra dimension, we find that the S parameter can be decreased by as much as 60%.;Finally we review models of structure formation and discuss the possibility of constraining new physics with galaxy cluster surveys. We find that for a large scatter in the luminosity-temperature relation, the cosmological parameters favored by galaxy cluster counts from the 400 Square Degree ROSAT survey are in agreement with the values found in the WMAP-3 year analysis. We explain why X-Ray surveys of galaxy cluster number counts are insensitive to new physics that would produce a dimming mechanism.

This thesis is concerned with strongly coupled extensions to the Standard Model. The majority of the thesis is dedicated to the study of Composite Higgs models, which are a proposed solution to the hierarchy problem of the electroweak scale. In these models the Higgs is a composite pseudo-Nambu Goldstone boson which forms a part of a new strongly interacting sector. There are many different variations on the basic Composite Higgs theme { the current status of some of these variations is assessed in light of results from the Large Hadron Collider. A new kind of Composite Higgs model is presented and studied, which features an alternative mechanism for the breaking of electroweak symmetry. A mechanism for deforming one model into another is also discussed, which might find application to the UV completion of Composite Higgs models. The formalism used in the Composite Higgs literature is also applied to the study of inflation, where the inflaton is assumed to be a pseudo-Nambu Goldstone boson arising from strongly coupled dynamics. A study of the inflaton potential is performed and its cosmological implications discussed. A different extension to the Standard Model with interesting phenomenological consequences is also studied. Quirks are strongly interacting particles whose masses are significantly higher than their confining scale. If produced in colliders, they leave unusual tracks which current searches are mostly blind to. A new search strategy for these hypothetical particles is proposed.

The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.

Alain Connes a découvert une approche algébrique à la géométrie en remplaçant la géométrie Riemannienne de spin ordinaire par des triplets spectraux. Un triplet spectral est un ensemble avec trois membres : une algèbre, un opérateur de Dirac et un espace de Hilbert. Toutes les informations géométriques de la variété sont codées dans les triplets spectraux. Une qualité nouvelle de cette reformulation est la possibilité d'inclure des espaces non commutatifs. Ils sont représentés par des algèbres non commutatives, alors que les espaces ordinaires sont codés par des algèbres commutatives. Il est maintenant possible de rendre les algèbres commutatives, qui représentent l'espace-temps, un petit peu non commutatives, en prenant le produit tensoriel avec une somme d'algèbres matricielles. Alain Connes et Ali Chamseddine ont découvert que, pour un certain choix d'algèbre matricielle, on obtient la relativité générale et la théorie de champ classique du modèle standard de la physique des particules. Les géométries presque-commutatifs offrent aussi une interprétation naturelle pour le boson de Higgs comme connexion dans la partie non commutative de la géométrie. Chaque triplet spectral presque-commutatif représente un modèle de Yang-Mills-Higgs et peut être un canditat potentiel pour une théorie physique. Dans cette thèse doctorale des restrictions physiques supplémentaires seront imposées sur les triplets spectraux, par exemple que les masses des fermions soient non-dégénérées et que la théorie soir renormalisable. A partir de ces principes fondamentaux tous les triplets spectraux presque-commutatifs ont été classifiés en collaboration avec les professeurs Thomas Schücker et Bruno Iochum, et avec Jan-Hendrik Jureit. Il est surprenant que le modèle standard de la physique des particules occupe une position proéminente dans cette classification. La question de savoir s'il y a des modèles physiques avec plus de quatre algèbres reste ouverte

In this dissertation we consider spacetime modifications that result in new physics beyond the standard model. We investigate various collider implications of a particular Lorentz-conserving formulation of QED in which spacetime coordinates are noncommuting. We also consider collider implications of Universal Extra Dimensions. Specifically, we address the possible formation of bound states involving the first quark KK-modes, i.e. KK-quarkonium. In addition, we consider the use of boundary conditions in extra dimensions to break gauge symmetries in unified theories. These boundary conditions can be related to a boundary Higgs sector that decouples from the theory. This technique of "Higgsless" symmetry breaking is applied to several models based on the trinified gauge group GT = SU(3)C x SU(3) L x SU(3)R. In addition, we analyze various phenomenological issues such as coupling unification and proton decay.

xviii, 124 p. : ill. (some col.)<br>This dissertation discusses three topics on scenarios beyond the Standard Model. Topic one is the effects from a fourth generation of quarks and leptons on electroweak baryogenesis in the early universe. The Standard Model is incapable of electroweak baryogenesis due to an insufficiently strong enough electroweak phase transition (EWPT) as well as insufficient CP violation. We show that the presence of heavy fourth generation fermions solves the first problem but requires additional bosons to be included to stabilize the electroweak vacuum. Introducing supersymmetric partners of the heavy fermions, we find that the EWPT can be made strong enough and new sources of CP violation are present. Topic two relates to the lepton avor problem in supersymmetry. In the Minimal Supersymmetric Standard Model (MSSM), the off-diagonal elements in the slepton mass matrix must be suppressed at the 10-3 level to avoid experimental bounds from lepton avor changing processes. This dissertation shows that an enlarged R-parity can alleviate the lepton avor problem. An analysis of all sensitive parameters was performed in the mass range below 1 TeV, and we find that slepton maximal mixing is possible without violating bounds from the lepton avor changing processes: μ [arrow right] eγ; μ [arrow right] e conversion, and μ [arrow right] 3e. Topic three is the collider phenomenology of quirky dark matter. In this model, quirks are particles that are gauged under the electroweak group, as well as a \dark" color SU (2) group. The hadronization scale of this color group is well below the quirk masses. As a result, the dark color strings never break. Quirk and anti-quirk pairs can be produced at the LHC. Once produced, they immediately form a bound state of high angular momentum. The quirk pair rapidly shed angular momentum by emitting soft radiation before they annihilate into observable signals. This dissertation presents the decay branching ratios of quirkonia where quirks obtain their masses through electroweak symmetry breaking. This dissertation includes previously published and unpublished co-authored material.<br>Committee in charge: Dr. Davison Soper: Chair; Dr. Graham Kribs: Advisor; Dr. Ray Frey: Member; Dr. Michael Kellman: Outside Member

This thesis is an investigation into the current bounds on the trilinear R–parity–violating couplings in the Minimal Supersymmetric Standard Model without R–parity conservation. The model is described, and its implications are discussed. Bounds on the couplings are obtained from leptonic and mesonic decay data, approximating mediating sfermions as much heavier than the decaying particles and assuming that only one set of couplings is non–zero for each decay. Those bounds from the purely leptonic decay data are compared to bounds from the LEP–II data, over a large range of sfermion masses. A potential signal of R–parity–violation at existing lepton colliders is calculated assuming that certain couplings are close to their bounds. The signal is found to be feasible and the backgrounds to the process are found to be negligible.

The formalism for a helicity amplitude analysis of the exclusive semileptonic decays of B mesons (B → Dlv and B → D* lv for l = e, µ and r) is introduced. In particular it is shown how measurements of the angular distribution of the subsequent decay D* → Dπ can fully determine the theoretically uncertain hadronic (B → D,D*) matrix elements. A spectator quark based model for the hadronic amplitudes is introduced, and then compared to other existing models and with the presently available experimental data, to extract the quark mixing matrix element |V(_eb)|. The extraction of |V(_ub)|, using exclusive models for b → u decays, is also discussed. The predictions of the free-quark model of inclusive semileptonic B decays are compared with those of the exclusive models, in an attempt to test the reliability of the inclusive model's predictions for |V(_eb)| and |V(_ub)|. A phenomenological analysis of experimental measurements of K(^0) – K(^0) and B(^0) – B(0) mixing is made, incorporating the above determinations of the mixing matrix elements, with a view to constraining the parameters of the standard model, such as the mass of the top-quark.