Ann E. Nelson

Effective field theory, black holes, and the cosmological constant

Bekenstein has proposed the bound S{le}{pi}M{sup 2}{sub P}L{sup 2} on the total entropy S in a volume L{sup 3} . This nonextensive scaling suggests that quantum field theory breaks down in large volume. To reconcile this breakdown with the success of local quantum field theory in describing observed particle phenomenology, we propose a relationship between UV and IR cutoffs such that an effective field theory should be a good description of nature. We discuss implications for the cosmological constant problem. We find a limitation on the accuracy which can be achieved by conventional effective field theory. {copyright} {ital 1999} {ital The American Physical Society}

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.}

Dynamical supersymmetry breaking at low energies.

Conventional approaches to supersymmetric model building suffer from several naturalness problems: they do not explain the large hierarchy between the weak scale and the Planck mass, and they require fine-tuning to avoid large flavor-changing neutral currents and particle electric dipole moments. The existence of models with dynamical supersymmetry breaking, which can explain the hierarchy, has been known for some time, but efforts to build such models have suffered from unwanted axions and difficulties with asymptotic freedom. In this paper we describe an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and give a realistic example.

Strange goings on in dense nucleonic matter

Abstract It has been suggested that charged pions form a Bose-Einstein condensate in baryonic matter at zero temperature and about twice nuclear density. In this letter it is shown that at somewhat higher densities one finds a charged kaon condensate, driven to a large extent by the “stgma term” interaction with baryons. Using the SU(3) × SU(3) chiral lagrangian to model meson-baryon interactions it is found that baryonic matter acquires a strangeness-per-baryon ratio approaching one at several times nuclear density. The relevance of kaon condensation as a route to strange matter and its role in neutron stars are discussed.

Progress in electroweak baryogenesis

Recent work on generating the excess of matter over antimatter in the early universe during the electroweak phase transition is reviewed.

The More minimal supersymmetric standard model

Abstract Effective Supersymmetry is presented as a theory of physics above the electroweak scale which has significant theoretical advantages over both the standard model and the Minimal Supersymmetric Standard Model (MSSM). The theory is supersymmetric at short distances but differs significantly from the MSSM. Flavor symmetry violation is intimately related to supersymmetry breaking. There is a new physics scale M ∼ 5–20 TeV which sets the mass of the first two sparticle families. Supersymmetric sources of CP violation and flavor changing neutral currents for the first two families are suppressed. Effective Supersymmetry can be implemented with automatic suppression of baryon and lepton number violation and a dynamically generated μ term, while maintaining naturalness in the Higgs sector. There are implications for new particle searches, flavor and CP violation experiments, as well as for the construction of theories of flavor and dynamical supersymmetry breaking.

Tests of the gravitational inverse square law

▪ Abstract We review recent experimental tests of the gravitational inverse-square law and the wide variety of theoretical considerations that suggest the law may break down in experimentally accessible regions.

Cosmological implications of dynamical supersymmetry breaking

We provide a taxonomy of dynamical supersymmetry-breaking theories, and discuss the cosmological implications of the various types of models. Models in which supersymmetry breaking is produced by chiral superfields which only have interactions of gravitational strength (e.g., string theory moduli) are inconsistent with standard big bang nucleosynthesis unless the gravitino mass is greater than [similar to]3[times]10[sup 4] GeV. This problem cannot be solved by inflation. Models in which supersymmetry is dynamically broken by renormalizable interactions in flat space have no such cosmological problems. Supersymmetry can be broken either in a hidden or the visible sector. However, hidden sector models suffer from several naturalness problems and have difficulties in producing an acceptably large gluino mass.

R symmetry breaking versus supersymmetry breaking

Abstract We point out a connection between R-symmetry and supersymmetry breaking. We show that the existence of an R-symmetry is a necessary condition for supersymmetry breaking and a spontaneously broken R-symmetry is a sufficient condition provided two conditions are satisfied. These conditions are: genericity, i.e. the effective lagrangian is a generic lagrangian consistent with the symmetries of the theory (no fine tuning), and calculability, i.e. the low-energy theory can be described by a supersymmetric Wess-Zumino effective lagrangian without gauge fields. All known models of dynamical supersymmetry breaking possess such a spontaneously broken R-symmetry and therefore contain a potentially troublesome axion. However, we use the fact that genericity is not a feature of supersymmetric theories, even when non-perturbative renormalization is included, to show that the R-symmetry can in many cases be explicitly broken without restoring supersymmetry and so the axion can be given an acceptably large mass.

Dirac Gaugino Masses and Supersoft Supersymmetry Breaking

We introduce a new supersymmetric extension of the standard model in which the gauge sector contains complete N = 2 supersymmetry multiplets. Supersymmetry breaking from the D-term vev of a hidden sector U(1) gauge field leads to Dirac soft supersymmetry breaking gaugino masses, and a new type of soft scalar trilinear couplings. The resulting squark and slepton masses are finite, calculable, positive and flavor universal. The Higgs soft mass squared is negative. The phenomenology of these theories differs significantly from the MSSM. We discuss a variety of possible origins for the soft operators and new fields, including models in both four and higher dimensions.