Mediated SUSY Breaking Research Articles

Search for gauge mediated SUSY breaking topologies in ee collisions at centre-of-mass energies up to 209 GeV

A total of 628$\invpb$ of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge mediated SUSY breaking (GMSB) topologies. These topologies include two acoplanar photons, non-pointing single photons, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons plus missing energy final states. No evidence is found for new phenomena, and lower limits on masses of supersymmetric particles are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the next-to-lightest supersymmetric particle (NLSP) mass at 54$\gevcc$ and for the mass scale parameter $\Lambda$ at 10$\tevcc$, independently of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77$\gevcc$ is obtained and values of $\Lambda$ up to 16$\tevcc$ are excluded.

Twisted Moduli and Supersymmetry Breaking

We consider twisted moduli contributions to supersymmetry breaking in effective type I string constructions involving intersecting D5_i and D9-branes using Goldstino angles to parametrise the supersymmetry breaking. It is well known that twisted moduli enter at tree-level into the gauge kinetic functions, and can provide new sources of gaugino mass if they develop F-term vacuum expectation values. It is generally assumed that string states which are sequestered from the twisted moduli receive a zero soft mass in the twisted modulus domination limit, however the standard form of Kahler potential does not reproduce this expectation. We therefore propose a new form of the Kahler potential which is consistent at leading order with the sequestered form proposed by Randall and Sundrum, and show that it leads to exponentially suppressed sequestered soft masses. Including the effects of Green-Schwarz mixing, we write down the soft scalar masses and trilinears arising from a type I string construction involving intersecting D5_i and D9-branes in the presence of untwisted and twisted moduli. If the squarks and sleptons are identified with sequestered states then in the twisted moduli dominated limit this corresponds to gaugino mediated supersymmetry breaking, and we discuss two different scenarios for this. The general results will be useful for phenomenological studies involving a combination of gravity and gaugino mediated SUSY breaking due to the dilaton, untwisted and twisted moduli contributions, and enable the soft masses to be studied as a function of the different compactification radii.

Reach of the Fermilab Tevatron and CERN LHC for gaugino mediated SUSY breaking models

In supersymmetric models with gaugino mediated SUSY breaking (inoMSB), it is assumed that SUSY breaking on a hidden brane is communicated to the visible brane via gauge superfields which propagate in the bulk. This leads to GUT models where the common gaugino mass $m_{1/2}$ is the only soft SUSY breaking term to receive contributions at tree level. To obtain a viable phenomenology, it is assumed that the gaugino mass is induced at some scale $M_c$ beyond the GUT scale, and that additional renormalization group running takes place between $M_c$ and $M_{GUT}$ as in a SUSY GUT. We assume an SU(5) SUSY GUT above the GUT scale, and compute the SUSY particle spectrum expected in models with inoMSB. We use the Monte Carlo program ISAJET to simulate signals within the inoMSB model, and compute the SUSY reach including cuts and triggers approriate to Fermilab Tevatron and CERN LHC experiments. We find no reach for SUSY by the Tevatron collider in the trilepton channel. %either with or without %identified tau leptons. At the CERN LHC, values of $m_{1/2}=1000$ (1160) GeV can be probed with 10 (100) fb$^{-1}$ of integrated luminosity, corresponding to a reach in terms of $m_{\tg}$ of 2150 (2500) GeV. The inoMSB model and mSUGRA can likely only be differentiated at a linear $e^+e^-$ collider with sufficient energy to produce sleptons and charginos.

4D constructions of supersymmetric extra dimensions and gaugino mediation

We present 4D gauge theories which at low energies coincide with higher dimensional supersymmetric (SUSY) gauge theories on a transverse lattice. We show that in the simplest case of pure 5D SUSY Yang-Mills there is an enhancement of SUSY in the continuum limit without fine-tuning. This result no longer holds in the presence of matter fields, in which case fine-tuning is necessary to ensure higher dimensional Lorentz invariance and supersymmetry. We use this construction to generate 4D models which mimic gaugino mediation of SUSY breaking. The way supersymmetry breaking is mediated in these models to the MSSM is by assuming that the physical gauginos are a mixture of a number of gauge eigenstate gauginos: one of these couples to the SUSY breaking sector, while another couples to the MSSM matter fields. The lattice can be as coarse as just two gauge groups while still obtaining the characteristic gaugino-mediated soft breaking terms.

Oscillating neutrinos and μ→ e, γ

If neutrino masses and mixings are suitable to explain the atmospheric and solar neutrino fluxes, this amounts to contributions to FCNC processes, in particular μ→ e, γ. If the theory is supersymmetric and the origin of the masses is a see-saw mechanism, we show that the prediction for BR( μ→ e, γ) is in general larger than the experimental upper bound, especially if the largest Yakawa coupling is O(1) and the solar data are explained by a large angle MSW effect, which recent analyses suggest as the preferred scenario. Our analysis is bottom–up and completely general, i.e., it is based just on observable low-energy data. The work generalizes previous results of the literature, identifying the dominant contributions. Application of the results to scenarios with approximate top-neutrino unification, like SO(10) models, rules out most of them unless the leptonic Yukawa matrices satisfy very precise requirements. Other possible ways-out, like gauge mediated SUSY breaking, are also discussed.

The -Problem and a Seesaw-Type Mechanism in the Higgs Sector

We explore a new solution to the $\mu$-problem. In the scenario of SUSY-breaking mediation through anti-generation fields, we find that the $B\mu$ term has its origin in a seesaw-type mechanism as well as in a loop diagram through gauge interactions. It is shown that the dominant contributions to the $B\mu$ term are controlled by the flavor symmetry in the model.

Impact of the muon anomalous magnetic moment on supersymmetric models

The recent measurement of a_\mu =\frac{g_\mu -2}{2} by the E821 Collaboration at Brookhaven deviates from the quoted Standard Model (SM) central value prediction by 2.6\sigma. The difference between SM theory and experiment may be easily accounted for in a variety of particle physics models employing weak scale supersymmetry (SUSY). Other supersymmetric models are distinctly disfavored. We evaluate a_\mu for various supersymmetric models, including minimal supergravity (mSUGRA), Yukawa unified SO(10) SUSY GUTs, models with inverted mass hierarchies (IMH), models with non-universal gaugino masses, gauge mediated SUSY breaking models (GMSB), anomaly-mediated SUSY breaking models (AMSB) and models with gaugino mediated SUSY breaking (inoMSB). Models with Yukawa coupling unification or multi-TeV first and second generation scalars are disfavored by the a_\mu measurement.

A new type of a stable Q-ball in gauge mediated SUSY breaking and its cosmology

We obtain a new type of a stable Q ball in the context of gauge-mediated supersymmetry breaking scenario. It is so-called gravity-mediation type of Q ball, but also stable against the decay into nucleons, since the energy per unit charge is equal to gravitino mass m 3 2 , which can be smaller than nucleon mass in the gauge-mediation mechanism. We consider the cosmological consequences in this new Q-ball scenario, and find that this new type of the Q ball can be considered as the dark matter and the source for the baryon number of the universe simultaneously.

Searches for prompt light gravitino signatures in e +e − collisions at [formula omitted] GeV

Searches for final states expected in models with light gravitinos have been performed, including experimental topologies with multi-leptons with missing energy, leptons and photons with missing energy, and jets and photons with missing energy. No excess over the expectations from the Standard Model has been observed. Limits are placed on production cross-sections in the different experimental topologies. Additionally, combining with searches for the anomalous production of lepton and photon pairs with missing energy, results are interpreted in the context of minimal models of gauge mediated SUSY breaking. Exclusion limits at the 95% confidence level on the supersymmetric particle masses of m ℓ ̃ > 83 GeV and m χ ̃ 1 0 > 85 GeV for tan β=2, and m τ ̃ > 69 GeV, m e ̃ , μ ̃ > 88 GeV and m χ ̃ 1 0 > 76 GeV for tan β=20, are established.

Improved GUT and SUSY breaking by the same field

In a previous paper, we presented a model in which the {\em same} modulus field breaks SUSY and a simple GUT gauge group, and which has {\em dynamical} origins for {\em both} SUSY breaking and GUT scales. In this model, the supergravity (SUGRA) and gauge mediated (GM) contributions to MSSM scalar and gaugino masses are comparable - this enables a realistic spectrum to be attained since GM contribution to the right-handed (RH) slepton (mass)^2 by itself (i.e., neglecting SUGRA contribution to sfermion {\em and} gaugino masses) is negative. But, in general, the SUGRA contribution to sfermion masses (from non-renormalizable contact K\"ahler terms) leads to flavor violation. In this paper, we use the recently proposed idea of gaugino mediated SUSY breaking (\tilde{g}MSB) to improve the above model. With MSSM matter and SUSY breaking fields localized on separate branes in an extra dimension of size R \sim 5 M^{-1}_{Pl} (in which gauge fields propagate), the SUGRA contribution to sfermion masses (which violates flavor) is suppressed. As in 4 dimensions, MSSM gauginos acquire {\em non}-universal masses from both SUGRA and GM - gaugino masses (in particular the SUGRA contribution to gaugino masses), in turn, generate acceptable sfermion masses through RG evolution; the phenomenology is discussed briefly. We also point out that a) in models where SUSY is broken by a GUT non-singlet field, there is, in general, a contribution to MSSM gaugino (and scalar) masses from the coupling to heavy gauge multiplet which {\em might} be {\em comparable} to the SUGRA contribution and b) models of GM proposed earlier which also have negative RH slepton (mass)^2 can be rendered viable using the \tilde{g}MSB idea.

Reach of the CERN LHC for the minimal anomaly-mediated SUSY breaking model

We examine the reach of the CERN LHC pp collider for supersymmetric models where the dominant contribution to soft SUSY breaking parameters arises from the superconformal anomaly. In the simplest viable anomaly mediated SUSY breaking (AMSB) model, tachyonic slepton squared masses are made positive by adding a universal contribution m 0 2 to all scalars. We use the event generator ISAJET to generate AMSB signal events as a function of model parameter space. Assuming an integrated luminosity of 10 fb −1, the LHC can reach to values of m g ̃ ∼2.5 TeV for low values of m 0, where the dilepton plus jets plus E / T channel offers the best reach. For large m 0, the best signature is typically 0 or 1 isolated lepton plus jets plus E / T ; in this case the reach is typically diminished to values of m g ̃ ∼1.3 TeV. The presence of terminating tracks in a subset of signal events could serve to verify the presence of a long lived chargino which is generic in the minimal AMSB model.

Impact of physical principles at very high energy scales on the superparticle mass spectrum

We survey a variety of proposals for new physics at high scales that serve to relate the multitude of soft supersymmetry breaking parameters of the MSSM. We focus on models where the new physics results in non-universal soft parameters, in sharp contrast with the usually assumed mSUGRA framework. These include {\it i}) SU(5) and SO(10) grand unified (GUT) models, {\it ii}) the MSSM plus a right-handed neutrino, {\it iii}) models with effective supersymmetry, {\it iv}) models with anomaly-mediated SUSY breaking and gaugino mediated SUSY breaking, {\it v}) models with non-universal soft terms due to string dynamics, and {\it vi}) models based on $M$-theory. We outline the physics behind these models, point out some distinctive features of the weak scale sparticle spectrum, and allude to implications for collider experiments. To facilitate future studies, for each of these scenarios, we describe how collider events can be generated using the program ISAJET. Our hope is that detailed studies of a variety of alternatives will help point to the physics underlying SUSY breaking and how this is mediated to the observable sector, once sparticles are discovered and their properties measured.

Phenomenology of flavor-mediated supersymmetry breaking

The phenomenology of a new economical SUSY model that utilizes dynamical SUSY breaking and gauge-mediation (GM) for the generation of the sparticle spectrum and the hierarchy of fermion masses is discussed. Similarities between the communication of SUSY breaking through a messenger sector, and the generation of flavor using the Froggatt-Nielsen (FN) mechanism are exploited, leading to the identification of vector-like messenger fields with FN fields, and the messenger U(1) as a flavor symmetry. An immediate consequence is that the first and second generation scalars acquire flavor-dependent masses, but do not violate FCNC bounds since their mass scale, consistent with effective SUSY, is of order 10 TeV. We define and advocate a minimal flavor-mediated model (MFMM), recently introduced in the literature, that successfully accommodates the small flavor-breaking parameters of the standard model using order one couplings and ratios of flavon field vevs. The mediation of SUSY breaking occurs via two-loop log-enhanced GM contributions, as well as several one-loop and two-loop Yukawa-mediated contributions for which we provide analytical expressions. The MFMM is parameterized by a small set of masses and couplings, with values restricted by several model constraints and experimental data. The next-to-lightest sparticle (NLSP) always has a decay length that is larger than the scale of a detector, and is either the lightest stau or the lightest neutralino. Similar to ordinary GM models, the best collider search strategies are, respectively, inclusive production of at least one highly ionizing track, or events with many taus plus missing energy. In addition, D^0 - \bar{D}^0 mixing is also a generic low energy signal. Finally, the dynamical generation of the neutrino masses is briefly discussed.

Higher dimensional operator corrections to the goldstino Goldberger–Treiman vertices

The goldstino-matter interactions given by the Goldberger-Treiman relations can receive higher dimensional operator corrections of $ O(q^{2}/M^{2})$, where $M$ denotes the mass of the mediators through which SUSY breaking is transmitted. These corrections in the gauge mediated SUSY breaking models arise from loop diagrams, and an explicit calculation of such corrections is presented. It is emphasized that the Goldberger-Treiman vertices are valid only below the mediator scale and at higher energies goldstinos decouple from the MSSM fields. The implication of this fact on gravitino cosmology in GMSB models is mentioned.

Gauge mediated supersymmetry breaking and neutrino anomalies

Supersymmetric standard model with softly broken lepton symmetry provides a suitable framework to accommodate the solar and atmospheric neutrino anomalies. This model contains a natural explanation for large mixing and hierarchal masses without fine tuning of the parameters. Neutrino spectrum is particularly constrained in the minimal messenger model (MMM) of gauge mediated SUSY breaking, since all SUSY breaking effects are controlled in MMM by a single parameter. We study the structure of neutrino masses and mixing both in MMM and in simple extensions of it in the context of solar and atmospheric neutrino anomalies.

Measurements in gauge mediated SUSY breaking models at the CERN LHC

Characteristic examples are presented of scenarios of particle production and decay in supersymmetry models in which the supersymmetry breaking is transmitted to the observable world via gauge interactions. The cases are chosen to illustrate the main classes of LHC phenomenology that can arise in these models. A new technique is illustrated that allows the full reconstruction of supersymmetry events despite the presence of two unobserved particles. This technique enables superparticle masses to be measured directly rather than being inferred from kinematic distributions. It is demonstrated that the LHC is capable of making sufficient measurements so as to severely over-constrain the model and determine the parameters with great precision.

Electric dipole moments in gauge mediated models and a solution to the SUSY CP problem

The SUSY CP problem in the framework of gauge mediated SUSY breaking model is considered. We first discuss the electric dipole moments of the electron and neutron, which are likely to be larger than the experimental upper bound if all the phases in the Lagrangian are O(1). We derive a constraint on the phases in the so-called μ- and B μ -parameters and gaugino masses. Then, we discuss a model in which the CP violating phase can be adequately suppressed. If the μ- and B μ -parameters originate from the same superpotential interaction as the SUSY breaking field, the CP violating phase vanishes. However, in this class of models, the ratio B μ / μ becomes too large, and we discuss a possible scenario to fix this problem.

Large squark and slepton masses for the first-two generations in the anomalous U(1) SUSY breaking models

Considering that the soft SUSY breaking scalar masses come from a vacuum expectation value of the D-term for an external gauge multiplet, the renormalization of the scalar masses is related to the gauge anomaly. Then, if the external gauge symmetry is anomaly-free and has no kinetic mixing with the other U(1) gauge symmetries, the scalar masses are non-renormalized at all orders assuming that the gaugino masses are negligibly small compared with the scalar masses. Motivated by this, we construct models where the sfermion masses for the first-two generations are much heavier than the other superparticles in the minimal SUSY standard model in a framework of the anomalous U(1) mediated SUSY breaking. In these models we have to introduce extra chiral multiplets with the masses as large as those for the first-two generation sfermions. We find that phenomenologically desirable patterns for the soft SUSY breaking terms can be obtained in the models.

Search for sleptons in e+e− collisions at centre–of–mass energies up to 184 GeV

The data collected by the ALEPH experiment at LEP at centre–of–mass energies around 183 GeV are analysed to search for sleptons, the partners of leptons in supersymmetric theories. The previously published search for acoplanar leptons and missing energy has been updated. New searches have been developed to cover a wider range of slepton signals. These include single electrons, acoplanar leptons accompanied by two photons plus missing energy as well as particles with lifetime. No evidence for the production of any such particles is found. Slepton mass limits are reported within gravity mediated and gauge mediated SUSY breaking scenarios.

Realistic GUT with gauge mediated supersymmetry breaking

We present an example of the gauge mediated SUSY breaking flipped SU(5) model. The messengers of the SUSY breaking are either only colour triplets which belong to the minimal content of the scalar supermultiplets or together with triplets as a messengers emerge the ordinary Higgs doublets. In both cases the model predicts light gauginos in respect of the squarks and sleptons, which could be tested in the nearest LEP experiments. In both cases ''all order`` solution of the doublet-triplet splitting problem is obtained, the $\mu $-term of the order of 100 GeV is generated and the left handed neutrino masses are suppressed.