Yosef Nir

New tools for low-energy dynamical supersymmetry breaking

We report the construction of large new classes of models which break supersymmetry dynamically. We then turn to model building. Two of the principal obstacles to constructing simple models of dynamical supersymmetry breaking are the appearance of Fayet-Iliopoulos {ital D} terms and difficulties in generating a {mu} term for the Higgs fields. Among the new models are examples in which symmetries prevent the appearance of Fayet-Iliopoulos terms. A gauge singlet field, which may play a role in explaining the hierarchy in quark and lepton parameters, can generate a suitable {mu} term. The result is a comparatively simple model, with a low energy structure similar to that of the MSSM, but with far fewer arbitrary parameters. We begin the study of the phenomenology of these models. {copyright} {ital 1996 The American Physical Society.}

The importance of flavor in leptogenesis

We study leptogenesis from the out-of-equilibrium decays of the lightest heavy neutrino N1 in the medium (low) temperature regime, T1012 GeV (109 GeV), where the rates of processes mediated by the τ (and μ) Yukawa coupling are non negligible, implying that the effects of lepton flavors must be taken into account. We find important quantitative and qualitative differences with respect to the case where flavor effects are ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of magnitude; (ii) The sign of the asymmetry can be opposite to what one would predict from the sign of the total lepton asymmetry 1; (iii) Successful leptogenesis is possible even with 1 = 0.

Flavor Physics Constraints for Physics Beyond the Standard Model

Over the past decade, much progress in experimentally measuring and theoretically understanding flavor physics has been achieved. Specifically, the accuracy of the determination of the CKM elements has been greatly improved, and a large number of (a) flavor-changing neutral-current processes involving b→d, b→s, and c→u transitions and (b) CP-violating asymmetries have been measured. No evidence for new physics has been established. Consequently, strong constraints on new physics at a high scale apply. In particular, the flavor structure of new physics at the teraelectronvolt scale is strongly constrained. We review these constraints and discuss future prospects to better understand the flavor structure of physics beyond the Standard Model.

Neutrino masses and mixing: Evidence and implications

Measurements of various features of the fluxes of atmospheric and solar neutrinos have provided evidence for neutrino oscillations and therefore for neutrino masses and mixing. We review the phenomenology of neutrino oscillations in vacuum and in matter. We present the existing evidence from solar and atmospheric neutrinos as well as the results from laboratory searches, including the final status of the LSND experiment. We describe the theoretical inputs that are used to interpret the experimental results in terms of neutrino oscillations. We derive the allowed ranges for the mass and mixing parameters in three frameworks: First, each set of observations is analyzed separately in a two-neutrino framework; Second, the data from solar and atmospheric neutrinos are analyzed in a three active neutrino framework; Third, the LSND results are added, and the status of accommodating all three signals in the framework of three active and one sterile light neutrinos is presented. We review the theoretical implications of these results: the existence of new physics, the estimate of the scale of this new physics and the lessons for grand unified theories, for supersymmetric models with R-parity violation, for models of extra dimensions and singlet fermions in the bulk, and for flavor models.

Should squarks be degenerate

Abstract For generic squark masses, box diagrams with squarks and gluinos give unacceptably large contributions to neutral meson (K, B and D) mixing. The standard solution to this problem is to assume that squarks are degenerate to a very good approximation. We suggest an alternative mechanism to suppress squark contributions to flavor changing neutral currents: the alignment of quark with squark mass matrices. This mechanism arises naturally in the framework of abelian horizontal symmetries.

Mass matrix models: The Sequel

Abstract The smallness of the quark sector parameters and the hierarchy between them could be the result of a horizontal symmetry broken by a small parameter. Such an explicitly broken symmetry can arise from an exact symmetry which is spontaneously broken. Constraints on the scales of new physics arise from new flavor-changing interactions and from Landau poles, but do not exclude the possibility of observable signatures at the TeV scale. Such a horizontal symmetry could also lead to many interesting results: (i) quark—squark alignment that would suppress, without squark degeneracy, flavor-changing neutral currents induced by supersymmetric particles, (ii) exact relations between mass ratios and mixing angles, (iii) a solution of the μ-problem and (iv) a natural mechanism for obtaining hierarchy among various symmetry-breaking scales.

Mass matrix models

Abstract It is possible that the hierarchy in the masses and mixing of quarks is a result of a horizontal symmetry. The smallness of various parameters is related to their suppression by high powers of a scale of new physics. We analyze in detail the structure of such symmetries in view of new experimental data and present explicit models consistent with all phenomenological constraints. We show that it is possible that the flavor dynamics can be at accessible energies - as low as a TeV.

KL → π0νν beyond the standard model☆

Abstract We analyze the decay K L → π 0 ν ν in a model independent way. If lepton flavor is conserved the final state is (to a good approximation) purely CP even. In that case this decay mode goes mainly through CP violating interference between mixing and decay. Consequently, a theoretically clean relation between the measured rate and electroweak parameters holds in any given model. Specificaly, Γ(K L → π 0 ν ν ) Γ(K + → π + ν ν ) = sin 2 θ (up to known isospin corrections), where θ is the relative CP violating phase between the K - K mixing amplitude and the s → dν ν decay amplitude. The experimental bound on BR (K + → π + ν ν ) provides a model independent upper bound: BR (K L → π 0 ν ν ) −8 . In models with lepton flavor violation, the final state is not necessarily a CP eigenstate. Then CP conserving contributions can dominate the decay rate.

New physics and CP violation in singly Cabibbo suppressed D decays

We analyze various theoretical aspects of

Variations on Minimal Gauge Mediated Supersymmetry Breaking

CP