Paul Langacker

Grand Unified Theories and Proton Decay

Grand unified theories, in which the strong and electroweak interactions are embedded into an underlying theory with a single gauge coupling constant, are reviewed. A detailed description is given of many of the necessary background topics, including gauge theories, spontaneous symmetry breaking, the standard SU2 x U1 electroweak model and its modifications and extensions, Majorana and Dirac neutrino masses, the induced cosmological term, CP violation, quantum chromodynamics and its symmetries, and dynamical symmetry breaking. The Georgi-Glashow SU5 model is examined in detail. Models based on unitary, orthogonal, exceptional, and semi-simple groups and general constraints on model building are surveyed. Phenomenological aspects of grand unified theories are described, including the determination of the unification mass, the prediction of sin2 θw in various models, existing and planned nucleon decay experiments, the predictions for the proton lifetime and branching ratios, general baryon number violating interactions, and the possible explanation of the matter-antimatter asymmetry of the universe. Other aspects of grand unified theories are discussed, including horizontal symmetries, neutrino and fermion masses, topless models, asymptotic freedom, implications for the neutral current, CP violation, superheavy magnetic monopoles, dynamical symmetry breaking, and the hierarchy problem.

TOWARD REALISTIC INTERSECTING D-BRANE MODELS

▪ Abstract We provide a pedagogical introduction to a recently studied class of phenomenologically interesting string models known as Intersecting D-Brane Models. The gauge fields of the Standard Model are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersections can give rise to chiral fermions. We address the basic issues and also provide an overview of the recent activity in this field. This article is intended to serve non-experts with explanations of the fundamental aspects of string phenomenology and also to provide some orientation for both experts and non-experts in this active field.

Theory of neutrinos: a white paper

This paper is a review of the present status of neutrino mass physics, which grew out of an APS sponsored study of neutrinos in 2004. After a discussion of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, it summarizes what can be learned about neutrino interactions as well as the nature of new physics beyond the Standard Model from the various proposed neutrino experiments. The intriguing possibility that neutrino mass physics may be at the heart of our understanding of a long standing puzzle of cosmology, i.e. the origin of matter?antimatter asymmetry is also discussed.

CERN LHC phenomenology of an extended standard model with a real scalar singlet

Gauge singlet extensions of the standard model (SM) scalar sector may help remedy its theoretical and phenomenological shortcomings while solving outstanding problems in cosmology. Depending on the symmetries of the scalar potential, such extensions may provide a viable candidate for the observed relic density of cold dark matter or a strong first order electroweak phase transition needed for electroweak baryogenesis. Using the simplest extension of the SM scalar sector with one real singlet field, we analyze the generic implications of a singlet-extended scalar sector for Higgs boson phenomenology at the Large Hadron Collider (LHC). We consider two broad scenarios: one in which the neutral SM Higgs and singlet mix and the other in which no mixing occurs and the singlet can be a dark matter particle. For the first scenario, we analyze constraints from electroweak precision observables and their implications for LHC Higgs phenomenology. For models in which the singlet is stable, we determine the conditions under which it can yield the observed relic density, compute the cross sections for direct detection in recoil experiments, and discuss the corresponding signatures at the LHC.

Physics at a future Neutrino Factory and super-beam facility

The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21–26 June 2005) and NuFact06 (Ivine, CA, 24–30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Superbeams, Laboratori Nazionali di Frascati, Rome, June 21-26, 2005) and NuFact06 (Irvine, California, 2430 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second generation super-beam experiments, beta-beam facilities, and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report. The ISS Physics Working Group Editors: S.F. King1, K. Long2, Y. Nagashima3, B.L. Roberts4, and O. Yasuda5.

Precision tests of the standard electroweak model

Part 1 The standard electroweak model: structure of the standard model, P. Langacker renormalization of the standard model, W. Hollik predictions for e+e- processes, W. Holik radiative corrections to neutral current processes, W. Marciano. Part 2 Precision tests at e+e-colliders: e+e- annihilation below the Z pole, D. Haidt and R. Marshall Z-pole experiments, D. Schaile polarization in e+e- annihilation, A. Blondel the LEP II program, D. Treille future e+e- colliders at high energy, D. Burke. Part 3 The weak neutral current: the measurement of electroweak parameters from deep inelastic neutrino scattering, F. Perrier elastic neutrino-nucleon scattering, A.K. Mann neutrino-electron scattering, J. Panman atomic parity violation experiments, C. Wieman the theory of atomic parity violation, J. Sapirstein charged lepton-hadron asymmetries in target experiments, P. Souder precision electroweak tests at HERA, H. Spiesberger. Part 4 The weak charged current: the unitarity of the Quark mixing matrix, A. Sirlin beta decay, right-handed currents and the search for new physics, J. Deutsch precision measurements in muon and tau decays, W. Fetscher and H.-J. Gerber muon decay and beta decay beyond the standard model, P. Herczeg. Part 5 Precision tests at hadron colliders, E. Einsweiler. Part 6 Implications of precision experiments: tests of the standard model and searches for new physics, P. Langacker exotic fermions, D. London. Part 7 The future, M Luo.

Uncertainties in coupling constant unification

The status of coupling constant unification in the standard model and its supersymmetric extension are discussed. Uncertainties associated with the input coupling constants,

Phase transitions and vacuum tunneling into charge and color breaking minima in the MSSM

{\mathit{m}}_{\mathit{t}}

Complex singlet extension of the standard model

, threshold corrections at the low and high scales, and possible nonrenormalizable operators are parametrized and estimated. A simple parametrization of a general supersymmetric new particle spectrum is given. It is shown that an effective scale

Implications of the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism of amplification of neutrino oscillations in matter

{\mathit{M}}_{\mathrm{SUSY}}