Searcharxiv⌕ Search

arXiv subjects

Ann E. Nelson

Publications and source records attributed to Ann E. Nelson.

69 records · Page 4Linked to original sources
arXiv1997

Contact Terms, Compositeness, and Atomic Parity Violation

The most severe constraints on quark-lepton four-fermion contact interactions come from the agreement of atomic parity violation measurements with the Standard Model. In this letter I note that for contact interactions which arise in theories of composite quarks and leptons, other approximate global symmetries than parity can eliminate the contribution of contact terms to atomic parity violation. The most stringent tests of compositeness therefore come from the high energy collider experiments at LEP II, HERA, and the Tevatron.

hep-ph↗
arXiv1997

Horizontal, Anomalous U(1) Symmetry for the More Minimal Supersymmetric Standard Model

We construct explicit examples with a horizontal, ``anomalous'' $U(1)$ gauge group, which, in a supersymmetric extension of the standard model, reproduce qualitative features of the fermion spectrum and CKM matrix, and suppress FCNC and proton decay rates without the imposition of global symmetries. We review the motivation for such ``more'' minimal supersymmetric standard models and their predictions for the sparticle spectrum. There is a mass hierarchy in the scalar sector which is the inverse of the fermion mass hierarchy. We show in detail why DeltaS = 2 FCNC are suppressed when compared with naive estimates for nondegenerate squarks.

hep-ph↗
arXiv1997

B-factory Physics from Effective Supersymmetry

We discuss how to extract non-Standard Model effects from B-factory phenomenology. We then analyze the prospects for uncovering evidence for Effective Supersymmetry, a class of supersymmetric models which naturally suppress flavor changing neutral currents and electric dipole moments without squark universality or small CP violating phases, in experiments at BaBar, BELLE, HERA-B, CDF/D0 and LHC-B.

hep-ph↗
arXiv1996

A Realistic Supersymmetric Model with Composite Quarks

We describe a realistic, renormalizable, supersymmetric ``quindecuplet'' model in which the top quark, left handed bottom quark, and up-type Higgs boson are composite, with a compositeness scale $\sim 1-3$ TeV. The top-Higgs Yukawa coupling is a dynamically generated strong interaction effect, and is naturally much larger than any other Yukawa coupling. The light quark doublets and right-handed up-type quarks are also composite but at higher energies; the hierarchy of quark masses and mixings is due to a hierarchy in the compositeness scales. Flavor changing neutral currents are naturally suppressed, as is baryon number violation by Planck-scale dimension five operators. The model predicts that the most easily observable effects would be on $b$-quark physics and on the $ρ$ parameter. In particular a small negative $Δρ=-ε$ leads to $ΔR_b> +2ε$. There are effects on $B$ meson mixing and on flavor-changing neutral-current $b$-quark decays to leptons which might be detectable, but not on $b\rightarrow sγ$. The model also suggests the supersymmetry-breaking mass for the right handed top squark might be considerably larger than that of the left handed top squark.

hep-ph↗
arXiv1996

Electroweak Baryogenesis in Supersymmetric Models

The baryon density which may be produced during the electroweak phase transition in supersymmetric models is computed, taking into account the previously neglected effects of transport, strong and weak anomalous fermion number violation, thermal scattering, and a new method for computing \cp\ violating processes during the transition. We can account for the observed baryon asymmetry, provided new \cp-violating phases are greater than $\sim 10^{-(2-4)}$, and some superpartners are light enough to be relevant during the transition, which takes place at a temperature of (50-100) GeV. In one case, light superpartners are the top squarks and the charginos and/or the neutralinos; in another case the top squarks and both Higgs doublets are light. Our calculation is easily extended to the case of a general two Higgs model, where we find sufficient baryogenesis provided that a certain combination of parameters in the Higgs potential leads to a \cp\ violating space dependent phase in the top quark mass of order $ 10^{-3}$.

hep-ph↗
arXiv1995

A Viable Model of Dynamical Supersymmetry Breaking in the Hidden Sector

We propose a simple and natural model of dynamical supersymmetry breaking, which could be used as a mechanism for spontaneous supersymmetry breaking in a gravitationally coupled hidden sector. The gaugino masses in the visible sector are naturally of the same size as the squark, slepton, and gravitino masses.

hep-ph↗
arXiv1995

New Issues In Low Energy Dynamical Supersymmetry Breaking

Comparatively simple models, with low energy structure similar to that of the MSSM, but with far fewer arbitrary parameters, can be constructed in which supersymmetry is dynamically broken at low energies. The phenomenology of these models is somewhat different than that of the usual scenario with supersymmetry broken in a hidden sector.

hep-ph↗
arXiv1995

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 D terms and difficulties in generating a $μ$ 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, that may play a role in explaining the hierarchy in quark and lepton parameters, can generate a suitable $μ$ 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.

hep-ph↗
arXiv1995

Consequences of Low Energy Dynamical Supersymmetry Breaking

Relatively simple models can be constructed in which supersymmetry is dynamically broken at energies of $10^5-10^7$ GeV. Models of this kind do not suffer from the naturalness and cosmological difficulties of conventional supergravity models, and make definite predictions for the spectrum of supersymmetric particle masses. Thus ``Renormalizable Visible Sector Models'' are a viable alternative to more conventional approaches. This talk mostly summarizes the results of a recent paper written with Michael Dine and Yuri Shirman.

hep-ph↗
arXiv1993

R Symmetry Breaking Versus Supersymmetry Breaking

We point out a connection between R symmetry and \susy\ breaking. We show that the existence of an R symmetry is a necessary condition for \susy\ breaking and a spontaneously broken R symmetry is a sufficient condition provided two conditions are satisfied. These conditions are: {\it genericity}, \ie\ the effective Lagrangian is a generic Lagrangian consistent with the symmetries of the theory (no fine tuning), and {\it calculability}, \ie\ 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 {\it not} a feature of supersymmetric theories, even when nonperturbative 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.

hep-ph↗
arXiv1993

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 (\eg\ string theory moduli) are inconsistent with standard big bang nucleosynthesis unless the gravitino mass is greater than $\CO(3) \times 10^4$ 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.

hep-ph↗
arXiv1993

Naturally Large Tan $β$

We show that if there are only two Higgs doublets in the supersymmetric standard model, large $\tanβ$ requires a fine tuning in the parameters of the Lagrangian of order ($1/\tanβ$), which cannot be explained by any approximate symmetry. With an extended Higgs sector, large $\tanβ$ can be natural. We give an explicit example with four doublets in which it is possible to achieve large $\tanβ$ as a result of an approximate symmetry, without any light superpartners. The approximate symmetry can be extended to explain all the hierarchies in the quark mass matrix.

hep-ph↗
arXiv1993

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.

hep-ph↗
arXiv1992

Is CP a Gauge Symmetry?

We suggest here that CP is a discrete {\it gauge} symmetry, and is therefore not violated by quantum gravity. We show that four dimensional CP can arise as a discrete gauge symmetry in theories with dimensional compactification, if the original number of Minkowski dimensions equals $8k+1$, $8k+2$ or $8k+3$, and if there are certain restrictions on the gauge group; these conditions are met by superstrings. CP may then be broken spontaneously below $10^9$ GeV, explaining the observed CP violation in the kaon system without inducing a large EDMN. We discuss the phenomenology of such models, as well as the peculiar nature of cosmic ``CP strings'' which could be produced at the compactification scale. Such strings have the curious property that a particle carried around the string is turned into its CP conjugate. A single CP string renders four dimensional spacetime nonorientable.

hep-ph↗