arXiv subjects

Ann E. Nelson

Publications and source records attributed to Ann E. Nelson.

At least 55 records · Page 3Linked to original sources

arXiv2003

Dynamical Electroweak Superconductivity from a Composite Little Higgs

I describe, from the bottom up, a sequence of natural effective field theories. Below a TeV we have the minimal standard model with a light Higgs, and an extra neutral scalar. In the 1-10 TeV region these scalars are part of a multiplet of pseudo Nambu-Goldstone Bosons. Interactions with additional TeV mass scalars, gauge bosons, and vector-like charge 2/3 quarks stabilize the Higgs mass squared parameter without finetuning. Electroweak superconductivity may be determined in this effective theory as a UV insensitive vacuum alignment problem. Above the 10 TeV scale we have strongly coupled new gauge interactions.

hep-ph↗

arXiv2002

The MSSM without mu term

We propose a supersymmetric extension of the standard model which does not have a ``mu'' supersymmetric Higgs mass parameter. The matter content of the MSSM is extended with three additional chiral superfields: one singlet, an SU(2) triplet and a color octet, and an approximate U(1)_R symmetry naturally guarantees that tan(beta) is large, explaining the top/bottom quark mass hierarchy. Unlike in the MSSM, there are significant upper bounds on the masses of superpartners, including an upper bound of 114 GeV on the mass of the lightest chargino. However the MSSM bound on the lightest Higgs mass does not apply.

hep-ph↗

arXiv2002

Extended Anomaly Mediation and New Physics at 10 TeV

In the MSSM, an unfortunate prediction of minimal anomaly mediated supersymmetry breaking is that the slepton masses squared are negative. This problem is particularly intractable because of the insensitivity of anomaly mediation to ultraviolet physics. In this paper we note that tree level couplings to the conformal compensator in the Kahler potential give 10 TeV as a natural mass scale for physics beyond the MSSM, and, moreover, that the SUSY breaking effects from physics at this scale do not generically decouple from the low-energy spectrum. We consider particular extensions, including the effects of vector-like matter at 10 TeV, and a specific model in which the leptons are placed in a triplet of an asymptotically free SU(3). We find that the features of minimal anomaly mediation are not a robust prediction of the general framework, and that the problem of negative slepton masses squared can easily be avoided.

hep-ph↗

arXiv2002

The Minimal Supersymmetric Model without a mu term

We propose a supersymmetric extension of the standard model which is a realistic alternative to the MSSM, and which has several advantages. No ``mu'' supersymmetric Higgs/Higgsino mass parameter is needed for sufficiently heavy charginos. An approximate U(1) R symmetry naturally guarantees that tan beta is large, explaining the top/bottom quark mass hierarchy. This symmetry also suppresses supersymmetric contributions to anomalous magnetic moments, b to s gamma, and proton decay, and these processes place no lower bounds on superpartner masses, even at large tan beta. The soft supersymmetry breaking mass parameters can easily be obtained from either gauge or Planck scale mediation, without the usual mu problem. Unlike in the MSSM, there are significant upper bounds on the masses of superpartners, including an upper bound of 114 GeV on the mass of the lightest chargino. However the MSSM bound on the lightest Higgs mass does not apply.

hep-ph↗

arXiv2002

Exact Results for Supersymmetric Renormalization and the Supersymmetric Flavor Problem

We explore the effects of a strongly-coupled, approximately scale-invariant sector on the renormalization of soft supersymmetry breaking terms. A useful formalism for deriving exact results for renormalization of soft supersymmetry breaking terms is given in an appendix, and used to generalize previously known results to include the effects of nontrilinear superpotential terms. We show that a class of theories which explain the flavor hierarchy without flavor symmetries can also solve the supersymmetric flavor problem by producing nearly degenerate masses for the first two generations of scalar superpartners within each charge sector. Effects from trilinear scalar terms are also suppressed, although their initial values must be relatively small. Our mechanism results in testable predictions for the superpartner spectrum.

hep-ph↗

arXiv2002

Gauge/Anomaly Syzygy and Generalized Brane World Models of Supersymmetry Breaking

In theories in which SUSY is broken on a brane separated from the MSSM matter fields, supersymmetry breaking is naturally mediated in a variety of ways. Absent other light fields in the theory, gravity will mediate supersymmetry breaking through the conformal anomaly. If gauge fields propagate in the extra dimension they, too, can mediate supersymmetry breaking effects. The presence of gauge fields in the bulk motivates us to consider the effects of new messenger fields with holomorphic and non-holomorphic couplings to the supersymmetry breaking sector. These can lead to contributions to the soft masses of MSSM fields which dramatically alter the features of brane world scenarios of supersymmetry breaking. In particular, they can solve the negative slepton mass squared problem of anomaly mediation and change the predictions of gaugino mediation.

hep-ph↗

arXiv2001

Large Extra Dimensions from a Small Extra Dimension

Models with extra dimensions have changed our understanding of the hierarchy problem. In general, these models explain the weakness of gravity by diluting gravity in a large bulk volume, or by localizing the graviton away from the standard model. In this paper, we show that the warped geometries necessary for the latter scenario can naturally induce the large volumes necessary for the former. We present a model in which a large volume is stabilized without supersymmetry. We comment on the phenomenology of this scenario and generalizations to additional dimensions.

hep-ph↗

arXiv2001

Lower Bound on the Propagation Speed of Gravity from Gravitational Cherenkov Radiation

Recently, interesting 4-D Lorentz violating models have been proposed, in which all particles have a common maximum velocity $c$, but gravity propagates (in the preferred frame) with a different maximum velocity $c_g \neq c$. We show that the case $c_g < c$ is very tightly constrained by the observation of the highest energy cosmic rays. Assuming a galactic origin for the cosmic rays gives a conservative bound of $c-c_g < 2 \times 10^{-15} c$; if the cosmic rays have an extragalactic origin the bound is orders of magnitude tighter, of order $c-c_g < 2 \times 10^{-19} c$.

hep-ph↗

arXiv2001

Testing m(up)=0 on the Lattice

A massless up quark is an intriguing solution to the strong CP problem. We discuss how lattice computations can be used in conjunction with chiral perturbation theory to address the consistency of $m_u=0$ with the observed hadron spectrum and interactions. It is not necessary to simulate very light quarks-three flavor partially quenched computations with comparable sea and valence quark masses on the order of the strange quark mass could suffice.

hep-lat↗

arXiv2000

Suppressing Flavor Anarchy

We present a new mechanism, which does not require any flavor symmetry, to explain the small Yukawa couplings and CKM mixing angles. The Yukawa matrices are assumed to be random at short distances and the hierarchical structure is generated in the infrared by renormalization group flow. The generic qualitative predictions of this mechanism are in good agreement with observation. We give several simple examples in supersymmetric theories. We show that our mechanism can also ameliorate the supersymmetric flavor problem, and make predictions for the superpartner mass spectrum. The mechanism is fully consistent with grand unification, and in SU(5)-based models of neutrino mass, predicts a large mixing angle for muon neutrino to tau neutrino oscillations.

hep-ph↗

arXiv1999

Gaugino Mediated Supersymmetry Breaking

We consider supersymmetric theories where the standard-model quark and lepton fields are localized on a "3-brane" in extra dimensions, while the gauge and Higgs fields propagate in the bulk. If supersymmetry is broken on another 3-brane, supersymmetry breaking is communicated to gauge and Higgs fields by direct higher-dimension interactions, and to quark and lepton fields via standard-model loops. We show that this gives rise to a realistic and predictive model for supersymmetry breaking. The size of the extra dimensions is required to be of order 10-100 times larger than fundamental scale (e.g. the string scale). The spectrum is similar to (but distinguishable from) the predictions of "no-scale" models. Flavor-changing neutral currents are naturally suppressed. The μterm can be generated by the Giudice-Masiero mechanism. The supersymmetric CP problem is naturally solved if CP violation occurs only on the observable sector 3-brane. These are the simplest models in the literature that solve all supersymmetric naturalness problems.

hep-ph↗

arXiv1999

Solar and Atmospheric Neutrino Oscillations from Bilinear R-Parity Violation

We discuss general predictions for neutrino masses and mixing angles from R parity violation in the Minimal Supersymmetric Standard Model. If the soft supersymmetry breaking terms are flavor blind at short distance, then the leptonic analogue of the CKM matrix depends on only two real parameters, which are completely determined by fits to solar and atmospheric neutrino oscillations. Either the small angle MSW, large angle MSW, or ``just-so'' solutions to the solar neutrino problem are allowed, although the large angle MSW solution requires substantial fine-tuning. The latter two cases require significant $ν_μ\toν_e$ oscillations of atmospheric neutrinos. We present a model which could explain bilinear R parity violation as a consequence of spontaneous symmetry violation by a dynamical supersymmetry breaking sector. The decay length and branching ratios of the LSP are estimated.

hep-ph↗

arXiv1999

Effective Field Theory, Black Holes, and the Cosmological Constant

Bekenstein has proposed the bound S < pi M_P^2 L^2 on the total entropy S in a volume L^3. This non-extensive 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: for example, the minimal correction to (g-2) for the electron from the constrained IR and UV cutoffs is larger than the contribution from the top quark.

hep-th↗

arXiv1998

Fermion Masses and Gauge Mediated Supersymmetry Breaking from a Single U(1)

We present a supersymmetric model of flavor. A single U(1) gauge group is responsible for both generating the flavor spectrum and communicating supersymmetry breaking to the visible sector. The problem of Flavor Changing Neutral Currents is overcome, in part using an `Effective Supersymmetry' spectrum among the squarks, with the first two generations very heavy. All masses are generated dynamically and the theory is completely renormalizable. The model contains a simple Froggatt-Nielsen sector and communicates supersymmetry breaking via gauge mediation without requiring a separate messenger sector. By forcing the theory to be consistent with SU(5) Grand Unification, the model predicts a large tan beta and a massless up quark. While respecting the experimental bounds on CP violation in the K-system, the model leads to a large enhancement of CP violation in B-(B bar) mixing as well as in B decay amplitudes.

hep-ph↗

arXiv1997

Dynamical Supersymmetry Breaking

I review the motivation for dynamical supersymmetry breaking, the various mechanisms which have been discovered, and the prospects for model building.

hep-ph↗

arXiv1997

New Multi-Scale Supersymmetric Models with Flavor Changing Neutral Current Suppression

We discuss the phenomenology of a class of supersymmetric models in which some of the quark and lepton superfields are an integral part of a dynamical supersymmetry breaking sector. The corresponding squarks and sleptons are much heavier than any other superpartners, and could naturally have masses as high as ~ 40 TeV. We discuss a general set of conditions for acceptable flavor-changing neutral currents and natural electroweak symmetry breaking, and identify two particularly interesting new classes of theories. We discuss how phenomenological signatures of such multi-scale models at the CERN LEP II and Fermilab Tevatron colliders could significantly differ from previously considered scenarios. In particular, we give experimental signals which could be present if the left-handed selectron is much lighter than the right-handed one.

hep-ph↗

arXiv1997

Counting 4 pi 's in Strongly Coupled Supersymmetry

We extend the "naive dimensional analysis" arguments used in QCD for estimating the strengths of operators in chiral Lagrangians to strongly coupled supersymmetric theories. In particular, we show how to count factors of 4 pi ---an inexact science, but nevertheless a useful art when such theories are used to model real particle physics.

hep-ph↗

arXiv1997

CP Violation and FCNC in the Third Family from Effective Supersymmetry

I discuss a ``more minimal'' modification of the minimal supersymmetric standard model, in which supersymmetry breaking is connected with the physics of flavor. Flavor Changing Neutral Currents (FCNC) for the first two families are suppressed, and for the third family may be of comparable size to the FCNC in the Standard Model.

hep-ph↗