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Elizabeth H. Simmons

Publications and source records attributed to Elizabeth H. Simmons.

At least 109 records · Page 6Linked to original sources
arXiv2001

Current Bounds on Technicolor with Scalars

Technicolor with scalars is the simplest dynamical symmetry breaking model and one in which the predicted values of many observables may be readily calculated. This letter applies current LEP, Tevatron, CESR, and SLAC data from searches for neutral and charged scalars and from studies of b-quark physics to obtain bounds on technicolor with scalars. Expectations for how upcoming measurements will further probe the theory's parameter space are also discussed.

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arXiv2001

Composite Scalars at LEP: Constraining Technicolor Theories

LEPI and LEPII data can be used to constrain technicolor models with light, neutral pseudo-Nambu-Goldstone bosons, Pa. We use published limits on branching ratios and cross sections for final states with photons, large missing energy, jet pairs, and b bbar pairs to constrain the anomalous Pa Z0 Z0, Pa Z0 photon, and Pa photon photon couplings. From these results, we derive bounds on the size of the technicolor gauge group and the number of technifermion doublets in models such as Low-scale Technicolor.

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arXiv2000

Top Physics

The Run I experiments at the Fermilab Tevatron Collider discovered the top quark and provided first measurements of many of its properties. Run II (and eventually the LHC and NLC experiments) promise to extend our knowledge of the top quark significantly. Understanding the top quark's large mass, and indeed the origin of all mass, appears to require physics beyond the Standard Model. Thus, the top quark may have unusual properties accessible to upcoming experiments.

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arXiv2000

Finding Z' bosons coupled preferentially to the third family at CERN LEP and the Fermilab Tevatron

Z' bosons that couple preferentially to the third generation fermions can arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1)) gauge groups. We show that existing limits on quark-lepton compositeness set by the LEP and Tevatron experiments translate into lower bounds of order a few hundred GeV on the masses of these Z' bosons. Resonances of this mass can be directly produced at the Tevatron. Accordingly, we explore in detail the limits that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We also comment on the possibility of using hadronically-decaying taus to improve the limits.

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arXiv2000

Strongly-Interacting Heavy Flavors Beyond the Standard Model

The origin of mass must lie in physics beyond the Standard Model. Dynamical electroweak symmetry breaking models like technicolor can generate masses for the W and Z bosons. Providing the large top quark mass and large top-bottom mass splitting while keeping rho parameter and flavor-changing neutral currents small requires new strong dynamics for the top and bottom quarks. In consequence, new particles are predicted at scales up to 10 TeV with signatures in jets or heavy flavors. Searches for these states are underway at Fermilab and LEP II.

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arXiv2000

Weak-Singlet Fermions: Models and Constraints

We employ data from precision electroweak tests and collider searches to derive constraints on the possibility that weak-singlet fermions mix with the ordinary Standard Model fermions. Our findings are presented within the context of a theory with weak-singlet partners for all ordinary fermions and theories in which only third-generation fermions mix with weak singlets. In addition, we indicate how certain results can be applied more widely in theories containing exotic fermions.

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arXiv1999

Thinking About Top: Looking Outside The Standard Model

The top quark is by far the heaviest known fermion [1]. In consequence, experiment is just beginning to explore its properties, and some of them may yet prove to be distinctly non-standard. The very size of the top quark's mass even hints at the possibility of a special role for top in electroweak symmetry breaking. This talk examines the top quark in the context of physics beyond the standard model, and discusses how Run II can help elucidate the true nature of top.

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arXiv1998

Dijet Mass Spectrum Limits on Flavor-Universal Colorons

Using recent D0 data on the dijet mass spectrum, we present a limit on flavor-universal colorons. At 95% CL we find Mc/cot(theta) > 837 GeV. We discuss the implications of this limit for models of quark compositeness, non-standard gluon interactions, and dynamical electroweak symmetry breaking. In addition, we place a lower bound Lambda_A8 > 2.1 TeV on the scale of color-octet axial-vector contact interactions among quarks which could arise in models of quark compositeness.

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arXiv1998

Top-Bottom Splitting in Technicolor with Composite Scalars

We present a model of dynamical electroweak symmetry breaking in which the splitting between the top and bottom quark masses arises naturally. The W and Z masses are produced by a minimal technicolor sector, the top quark mass is given by the exchange of a weak-doublet technicolored scalar, and the other quark and lepton masses are induced by the exchange of a weak-doublet technicolor-singlet scalar. We show that, in the presence of the latter scalar, the vacuum alignment is correct even in the case of SU(2) technicolor. The fit of this model to the electroweak data gives an acceptable agreement (chi-squared = 28 for 20 degrees of freedom). The mass hierarchy between the standard fermions other than top can also be explained in terms of the hierarchy of squared-masses of some additional scalars. We discuss various possibilities for the compositeness of the scalars introduced here.

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arXiv1998

A Heavy Top Quark From Flavor-Universal Colorons

Ordinary technicolor and extended technicolor cannot produce the heavy top quark unaided. We demonstrate that a flavor-universal extension of the color interactions combined with an extended hypercharge sector that singles out the third generation can provide the necessary assistance. We discuss current experimental constraints and suggest how collider experiments can search for the predicted new heavy gauge bosons.

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arXiv1996

$Z\to b\bar b$ in $U(1)_R$ Symmetric Supersymmetry

We compute the one-loop corrections to the $Z \to b\bar{b}$ vertex in the $U(1)_R$ symmetric minimal supersymmetric extension of the standard model. We find that the predicted value of $R_b$ is consistent with experiment if the mass of the lighter top squark is no more than 180 GeV. Furthermore, other data combines to place a lower bound of 88 GeV on the mass of the light top squark. A top squark in this mass range should be accessible to searches by experiments at FNAL and LEP.

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arXiv1995

Limits on Pseudoscalar Bosons From Rare $Z$ Decays at LEP

Current LEP data on rare $Z$ decays constrain nonminimal technicolor models that contain light neutral pseudo-Nambu-Goldstone bosons ($P^a$). We discuss the production and decay of such particles, and show how LEP data on $γγγ$, $γ+ E\!\!\!/ $ and $γ+$hadrons constrain the size of the technicolor gauge group and the strength of the $ZγP^a$ coupling. The limits are then applied to several specific technicolor scenarios.

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arXiv1995

Strongly Coupled Electroweak Symmetry Breaking: Implications of Models

We discuss the phenomenology of models of dynamical electroweak symmetry breaking which attempt to generate the observed fermion mass spectrum. After briefly describing the variety of and constraints on proposed models, we concentrate on the signatures of colored pseudo-Nambu-Goldstone bosons and resonances at existing and proposed colliders. These particles provide a possibly unique signature: strongly produced resonances associated with electroweak symmetry breaking. (This is the subgroup report for the ``Electroweak Symmetry Breaking and Beyond the Standard Model" working group of the DPF Long Range Planning Study. This report will appear as a chapter in ``Electroweak Symmetry Breaking and Beyond the Standard Model", edited by T. Barklow, S. Dawson, H.E. Haber, and J. Siegrist, to be published by World Scientific.)

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arXiv1994

b \rightarrow s γAND Z \rightarrow b \overline{b} IN TECHNICOLOR WITH SCALARS

We consider the radiative decay $b\rightarrow s γ$, and the correction to the $Zb\overline{b}$ vertex in technicolor models with scalars. In these models, the scalar develops a vacuum expectation value when the technifermions condense, and the ordinary fermions develop masses via Yukawa couplings. Since the symmetry breaking sector involves both a fundamental scalar doublet and an isotriplet of composite scalars (the technipions), the phenomenology associated with the charged scalars is similar to that found in a type-I two-Higgs doublet model. We show that the correction to the $Zb\overline{b}$ vertex is small over the allowed parameter space of the model in the two limits that we consider, and that there can be large, potentially observable, contributions to the $b\rightarrow s γ$ branching fraction.

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arXiv1993

The Hunting of the MR Model

We consider experimental signatures of the standard model's minimal supersymmetric extension with a continuous $U(1)_R$ symmetry (MR model). We focus on the ability of existing and planned electron-positron colliders to probe this model and to distinguish it from both the standard model and the standard model's minimal supersymmetric extension with a discrete $R$-parity.

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arXiv1992

Critical Constraints on Chiral Hierarchies

We consider the constraints that critical dynamics places on models with a top quark condensate or strong extended technicolor (ETC). These models require that chiral-symmetry-breaking dynamics at a high energy scale plays a significant role in electroweak symmetry breaking. In order for there to be a large hierarchy between the scale of the high energy dynamics and the weak scale, the high energy theory must have a second order chiral phase transition. If the transition is second order, then close to the transition the theory may be described in terms of a low-energy effective Lagrangian with composite ``Higgs'' scalars. However, scalar theories in which there are more than one $Φ^4$ coupling can have a {\it first order} phase transition instead, due to the Coleman-Weinberg instability. Therefore, top-condensate or strong ETC theories in which the composite scalars have more than one $Φ^4$ coupling cannot always support a large hierarchy. In particular, if the Nambu--Jona-Lasinio model solved in the large-$N_c$ limit is a good approximation to the high-energy dynamics, then these models will not produce acceptable electroweak symmetry breaking.

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