Flavor Symmetries and Fermion Masses


Book Description

We introduce several ways in which approximate flavor symmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutrality of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand unified theories are discussed. First, we show that the successful predictions for the Kobayashi-Maskawa mixing matrix elements, V{sub ub}/V{sub cb} = √m{sub u}/m{sub c} and V{sub td}/V{sub ts} = √m{sub d}/m{sub s}, are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay [beta] → s[gamma] constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tan[Beta], is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.




A Domino Theory of Flavor


Book Description

We argue that the fermion masses and mixings are organized in a specific pattern. The approximately equal hierarchies between successive generations, the sizes of the mixing angles, the heaviness of just the top quark, and the approximate down-lepton equality can all be accommodated by many flavor models but can appear ad hoc. We present a simple, predictive mechanism to explain these patterns. All generations are treated democratically and the flavor symmetries are broken collectively by only two allowed couplings in flavor-space, a vector and matrix, with arbitrary [Omicron](1) entries. Repeated use of these flavor symmetry breaking spurions radiatively generates the Yukawa couplings with a natural hierarchy. We demonstrate this idea with two models in a split supersymmetric grand unified framework, with minimal additional particle content at the unification scale. Although flavor is generated at the GUT scale, there are several potentially testable predictions. In our minimal model the usual prediction of exact b-[tau] unification is replaced by the SU(5) breaking relation m{sub {tau}}/m{sub b} = 3/2, in better agreement with observations. Other SU(5) breaking effects in the fermion masses can easily arise directly from the flavor model itself. The symmetry breaking that triggers the generation of flavor necessarily gives rise to an axion, solving the strong CP problem. These theories contain long-lived particles whose decays could give striking signatures at the LHC and may solve the primordial Lithium problems. These models also give novel proton decay signatures which can be probed by the next generation of experiments. Measurement of the various proton decay channels directly probes the flavor symmetry breaking couplings. In this scenario the Higgs mass is predicted to lie in a range near 150 GeV.




An Explicit SU(12) Family and Flavor Unification Model with Natural Fermion Masses and Mixings


Book Description

We present an SU(12) unification model with three light chiral families, avoiding any external flavor symmetries. The hierarchy of quark and lepton masses and mixings is explained by higher dimensional Yukawa interactions involving Higgs bosons that contain SU(5) singlet fields with VEVs about 50 times smaller than the SU(12) unification scale. The presented model has been analyzed in detail and found to be in very good agreement with the observed quark and lepton masses and mixings.




From My Vast Repertoire...: Guido Altarelli's Legacy


Book Description

'What makes this collection unusual and refreshing is that it is not the more common ‘Festschrift’ written by specialists for specialists, but a broad set of topical summaries and analyses addressed to a wide readership of particle physicists. Inevitably, some of the sections are more advanced in their treatment than others, but most of the material will be accessible and helpful to researchers at all levels, and in particular to those working on experiments at CERN, where Altarelli spent many years in the theory group. It is hard to do justice to the varied contents of this excellent collection … I can only recommend that anyone involved in particle research should turn to the web for a full description of the richness of material that is included here … There is something here for everyone, and much for most. I’m sure Altarelli would have been pleased with that! The Editors are to be complimented for their initiative in making this unique volume possible.'Contemporary PhysicsGuido Altarelli was a leading figure in 20th century particle physics. His scientific contributions and leadership played a key role in the development of the Standard Model of fundamental interactions, as well as the current search for new physics beyond it, both at and beyond CERN. This book is a collection of original contributions, at the cutting edge of scientific research, by some of the leading theoretical and experimental high-energy physicists currently in the field. These were inspired by Guido's ideas, whether directly or indirectly. This book is ideal for researchers looking to keep up with the latest developments in high-energy physics.




An Introduction to Non-Abelian Discrete Symmetries for Particle Physicists


Book Description

These lecture notes provide a tutorial review of non-Abelian discrete groups and show some applications to issues in physics where discrete symmetries constitute an important principle for model building in particle physics. While Abelian discrete symmetries are often imposed in order to control couplings for particle physics - in particular model building beyond the standard model - non-Abelian discrete symmetries have been applied to understand the three-generation flavor structure in particular. Indeed, non-Abelian discrete symmetries are considered to be the most attractive choice for the flavor sector: model builders have tried to derive experimental values of quark and lepton masses, and mixing angles by assuming non-Abelian discrete flavor symmetries of quarks and leptons, yet, lepton mixing has already been intensively discussed in this context, as well. The possible origins of the non-Abelian discrete symmetry for flavors is another topic of interest, as they can arise from an underlying theory - e.g. the string theory or compactification via orbifolding – thereby providing a possible bridge between the underlying theory and the corresponding low-energy sector of particle physics. This text explicitly introduces and studies the group-theoretical aspects of many concrete groups and shows how to derive conjugacy classes, characters, representations, and tensor products for these groups (with a finite number) when algebraic relations are given, thereby enabling readers to apply this to other groups of interest.




U(2) Flavor Physics Without U(2) Symmetry


Book Description

The authors present a model of fermion masses based on a minimal, non-Abelian discrete symmetry that reproduces the Yukawa matrices usually associated with U(2) theories of flavor. Mass and mixing angle relations that follow from the simple form of the quark and charged lepton Yukawa textures are therefore common to both theories. They show that the differing representation structure of the horizontal symmetry allows for new solutions to the solar and atmospheric neutrino problems that do not involve modification of the original charged fermion Yukawa textures, or the introduction of sterile neutrinos.




Flavor Physics for the Millennium


Book Description

This book is devoted to the broad subject of flavor physics, embracing the question of what distinguishes one type of elementary particles from another. The articles range from the forefront of formal theory (treating the physics of extra dimensions) to details of particle detectors. Although special emphasis is placed on the physics of kaons, charmed and beauty particles, top quarks, and neutrinos, the articles also dealing with electroweak physics, quantum chromodynamics, supersymmetry, and dynamical electroweak symmetry breaking. Violations of fundamental symmetries such as time reversal invariance are discussed in the context of neutral kaons, beauty particles, electric dipole moments, and parity violation in atoms. The physics of the CabibboOCoKobayashiOCoMaskawa matrix and of quark masses are described in some detail, both from the standpoint of present and future experimental knowledge and from a more fundamental viewpoint, where physicists are still searching for the correct theory. Contents: The Electroweak Theory (C Quigg); CP Violation (L Wolfenstein); Precision Electroweak Physics (Y-K Kim); Kaon and Charm Physics: Theory (G Buchalla); Kaon Physics: Experiments (T Barker); The Status of Mixing in the Charm Sector (J P Cumalat); Basics of QCD Perturbation Theory (D E Soper); Lattice QCD and the CKM Matrix (T DeGrand); The Strong CP Problem (M Dine); A Bibliography of Atomic Parity Violation and Electric Dipole Moment Experiments (C E Wieman); The CKM Matrix and the Heavy Quark Expansion (A F Falk); CP Violation in B Decays (J L Rosner); Lectures on the Theory of Nonleptonic B Decays (M Neubert); Asymmetrical e Collisions (A Roodman); Pathological Science (S Stone); Top Physics (E H Simmons); Neutrino Mass, Mixing, and Oscillation (B Kayser); Flavor in Supersymmetry (H Murayama); Technicolor and Compositeness (R S Chivukula); Models of Fermion Masses (G G Ross); Physics of Extra Dimensions (J D Lykken). Readership: Graduate students, postdoctoral fellows and senior researchers in high energy physics."




Discrete Flavour Symmetries


Book Description

The flavour puzzle is an open problem both in the Standard Model and in its possible supersymmetric or grand unified extensions. In this monograph, we discuss possible explanations of the origin of fermion mass hierarchies and mixings by the use of non-Abelian discrete flavour symmetries. We present several realisations in which the flavour symmetry contains either the double-valued group T' or the permutation group S4: the spontaneous breaking of the flavour symmetry produces realistic fermion mass hierarchies and mixing schemes. We consider also the constraints on flavour violating processes arising from introducing a flavour symmetry: in particular we concentrate on the lepton sector, analysing some lepton flavour violating decays and the discrepancy between the theoretical prediction and the experimental measurement of the anomalous magnetic moment of the muon. We develop the study both in the Standard Model scenario and in its minimal supersymmetric extension, using at first an effective operator approach and then a complete loop computation. Interesting hints for the scale of New Physics and for the forthcoming experimental results from LHC are found.




Neutrinos in High Energy and Astroparticle Physics


Book Description

This self-contained modern textbook provides a modern description of the Standard Model and its main extensions from the perspective of neutrino physics. In particular it includes a thorough discussion of the varieties of seesaw mechanism, with or without supersymmetry. It also discusses schemes where neutrino mass arises from lighter messengers, which might lie within reach of the world's largest particle accelerator, the Large Hadron Collider. Throughout the text, the book stresses the role of neutrinos due to the fact that neutrino properties may serve as a guide to the correct model of unification, hence for a deeper understanding of high energy physics, and because neutrinos play an important role in astroparticle physics and cosmology. Each chapter includes summaries and set of problems, as well as further reading.