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Jonathan A. Bagger

Publications and source records attributed to Jonathan A. Bagger.

18 recordsLinked to original sources
arXiv2007

Decoupling and Destabilizing in Spontaneously Broken Supersymmetry

The supersymmetric analog of the Goldberger-Treiman relation plays a critical role in the low energy effective theory of models in which supersymmetry is spontaneously broken in a hidden sector. The interactions that connect the hidden and visible sectors break a global symmetry, which implies that the low energy theory must be constructed consistently in inverse powers of the messenger scale. The Goldberger-Treiman relation determines the couplings of the Goldstino to the visible sector fields. These couplings are fixed by the soft supersymmetry breaking terms within a power counting scheme that is stable under radiative corrections. We describe the power counting of the low energy effective theory, first for a toy model of extended technicolor and then for the supersymmetric standard model. One implication of this work for supersymmetry phenomenology is the observation that Goldstino loops can destabilize the weak scale if the low energy theory is not constructed consistently. Another is that Goldstino loops induce all visible sector operators not forbidden by symmetries. The magnitudes of these operators are determined by the consistent power counting of the low energy effective theory.

hep-ph↗
arXiv2004

Brane-Localized Goldstone Fermions in Bulk Supergravity

We construct the action and transformation laws for bulk five-dimensional AdS supergravity coupled to one or two brane-localized Goldstone fermions. The resulting bulk-plus-brane system gives a model-independent description of brane-localized supersymmetry breaking in the Randall-Sundrum scenario. We explicitly reduce the action and transformation laws to spontaneously broken four-dimensional supergravity.

hep-th↗
arXiv1999

Superheavy Supersymmetry from Scalar Mass--A Parameter Fixed Points

In supersymmetric models, the well-known tension between naturalness and experimental constraints is relieved if the squarks and sleptons of the first two generations are superheavy, with masses of order 10 TeV, and all other superpartners are light, with masses of order 1 TeV. We show that even if all scalar masses and trilinear A parameters are of order 10 TeV at some high scale, a mass-squared hierarchy of order 400 may be generated dynamically through renormalization group evolution. The required high energy relations are consistent with grand unification, or, alternatively, may be realized in moduli-dominated supersymmetry-breaking scenarios.

hep-ph↗
arXiv1999

Precision Observables and Electroweak Theories

We compute the bounds from precision observables on alternative theories of electroweak symmetry breaking. We show that a cut-off as large as 3 TeV can be accomodated by the present data, without unnatural fine tuning.

hep-ph↗
arXiv1998

New supersymmetry algebras from partial supersymmetry breaking

In this talk we will study the partial breaking of supersymmetry in flat and anti de Sitter space. We will see that partial breaking in flat space can be accomplished using either of two representations for the massive N=1 spin-3/2 multiplet. We will "unHiggs" each representation and find a new N=2 supergravity and a new N=2 supersymmetry algebra. We will also see that partial supersymmetry breaking in AdS space can give rise to a new N=2 supersymmetry algebra, one that is necessarily nonlinearly realized.

hep-th↗
arXiv1997

Supersymmetry at LHC and NLC

This talk discusses the prospects for supersymmetry studies at the LHC and NLC. The results are based on those of the Supersymmetry Working Group at the 1996 Snowmass Workshop.

hep-ph↗
arXiv1997

QCD Corrections to Flavor-Changing Neutral Currents in the Supersymmetric Standard Model

We compute the leading QCD corrections to K-Kbar mixing in the supersymmetric standard model with general soft supersymmetry-breaking parameters. We construct the ΔS=2 effective Lagrangian for three hierarchies of supersymmetric particle masses, namely, when the gluino mass is comparable to, much greater than, or much less than the masses of the first two generation squarks. We find that the QCD corrections tighten the limits on squark mass splittings by more than a factor of two.

hep-ph↗
arXiv1997

Precision Corrections in the Minimal Supersymmetric Standard Model

In this paper we compute one-loop corrections to masses and couplings in the minimal supersymmetric standard model. We present explicit formulae for the complete corrections and a set of compact approximations which hold over the unified parameter space associated with radiative electroweak symmetry breaking. We illustrate the importance of the corrections and the accuracy of our approximations by scanning over the parameter space. We calculate the supersymmetric one-loop corrections to the W-boson mass, the effective weak mixing angle, and the quark and lepton masses, and discuss implications for gauge and Yukawa coupling unification. We also compute the one-loop corrections to the entire superpartner and Higgs-boson mass spectrum. We find significant corrections over much of the parameter space, and illustrate that our approximations are good to O(1%) for many of the superparticle masses.

hep-ph↗
arXiv1997

Gauge and Yukawa Unification in Models with Gauge-Mediated Supersymmetry Breaking

We examine gauge and Yukawa coupling unification in models with gauge-mediated supersymmetry breaking. We work consistently to two-loop order, and include all weak, messenger and unification-scale threshold corrections. We find that successful unification requires unification-scale threshold corrections that are in conflict with the minimal SU(5) model, but are consistent with the modified missing doublet SU(5) model for small tan beta, and large tan beta with mu>0.

hep-ph↗
arXiv1996

Weak-scale phenomenology of models with gauge-mediated supersymmetry breaking

We study in some detail the spectral phenomenology of models in which supersymmetry is dynamically broken and transmitted to the supersymmetric partners of the quarks, leptons and gauge bosons, and the Higgs bosons themselves, via the usual gauge interactions. We elucidate the parameter space of what we consider to be the minimal model, and explore the regions which give rise to consistent radiative electroweak symmetry breaking. We include the weak-scale threshold corrections, and show how they considerably reduce the scale dependence of the results. We examine the sensitivity of our results to unknown higher-order messenger-sector corrections. We compute the superpartner spectrum across the entire parameter space, and compare it to that of the minimal supergravity-inspired model. We delineate the regions where the lightest neutralino or tau slepton is the next-to-lightest supersymmetric particle, and compute the lifetime and branching ratios of the NLSP. In contrast to the minimal supergravity-inspired model, we find that the lightest neutralino can have a large Higgsino component, of order 50%. Nevertheless, the neutralino branching fraction to the gravitino and the light Higgs boson remains small, < 10^{-4}, so the observation of such a decay would point to a non-minimal Higgs sector.

hep-ph↗
arXiv1996

Weak-Scale Supersymmetry: Theory and Practice

These lectures contain an introduction to the theory and practice of weak-scale supersymmetry. They begin with a discussion of the hierarchy problem and the motivation for weak-scale supersymmetry. They continue by developing the coset approach to superfields. They use superfield techniques to construct the minimal supersymmetric version of the standard model and to discuss soft supersymmetry breaking and its implications. The lectures end with a brief survey of expectations for future collider experiments.

hep-ph↗
arXiv1995

Destabilizing Divergences in Supergravity Theories

We study the stability of the gauge hierarchy in hidden-sector supergravity theories. We show that a destabilizing tadpole can appear if a theory has a gauge- and global-symmetry singlet with renormalizable couplings to the visible fields. We also find a quadratically divergent two-loop contribution to the supersymmetric effective potential. This term illustrates the difficulty of using the "LHC mechanism" to control quadratic divergences in theories with Planck-scale vevs.

hep-ph↗
arXiv1995

The Status of Supersymmetry

Supersymmetry searches are about to enter an important new era. With LEP 200 and the Main Injector, they will, for the first time, begin to probe significant regions of the supersymmetric parameter space. There is a real chance that supersymmetry might indeed be found before the advent of the LHC.

hep-ph↗
arXiv1993

Electroweak Symmetry Breaking at the Supercollider

Invited talk presented at the Workshop on Physics at Current Accelerators and the Supercollider, Argonne, Illinois, and at the 17th Johns Hopkins Workshop on Current Problems in Particle Theory, Budapest, Hungary.

hep-ph↗
arXiv1992

Electroweak Symmetry Breaking at the SSC and LHC

In this talk we survey the SSC and LHC signals and backgrounds for the physics of electroweak symmetry breaking. We study the process $pp \rightarrow WWX$ and compute the rate for the ``gold-plated'' signals $W^\pm \rightarrow \ell^\pm ν$ and $Z \rightarrow \ell^+\ell^-$ $(\ell = e,μ)$ for a wide variety of models. We use a forward jet tag and central jet veto to suppress the standard-model backgrounds. In this way we estimate the SSC and LHC sensitivities to the physics of electroweak symmetry breaking.

hep-ph↗
arXiv1992

Observing Electroweak Symmetry Breaking at the SSC

In this talk we survey the SSC signals and backgrounds for the physics of electroweak symmetry breaking. We study the process $pp \rightarrow WWX$ and compute the rate for the ``gold-plated'' signals $W^\pm \rightarrow \ell^\pm ν$ and $Z \rightarrow \ell^+\ell^-$ $(\ell = e,μ)$ for a wide variety of models. We use a forward jet tag and central jet veto to suppress the standard-model backgrounds. In this way we estimate the SSC sensitivity to the physics of electroweak symmetry breaking. (Revised version contains style file ichep.sty.)

hep-ph↗
arXiv1992

Quantum Corrections to Deep Bags

Nontopological solitons, or ``bags,'' can arise when fermions acquire their mass through a Yukawa coupling to some scalar field. Bags have played an important role in models of baryons, nuclei, and more recently, in the idea that a Higgs condensate may form around a very heavy top quark. It has been claimed that deep bags, which correspond to tightly-bound states of fermions, will form when the Yukawa coupling is strong. Quantum corrections, however, are significant in this regime. We examine the effects of these quantum corrections on the formation of nontopological solitons in an exactly solvable large-$N$ model. We find that quantum bags differ dramatically from those of the classical theory. In particular, for large Yukawa coupling, the bags remain shallow and the fermions weakly bound.

hep-ph↗