Scales, couplings revisited and low-energy phenomenology in M-theory on S^1/Z_2

We reconsider the dimension-11 Planck scale, the physical scale of the eleventh dimension, the physical scale of the Calabi–Yau manifold and the coupling in the hidden sector in M-theory on . Also we discuss reasonable bounds on them. Considering the F-term of the dilaton and moduli SUSY breaking and choosing two representative points which correspond to the scalar quasi-massless scenario and the dilaton dominant SUSY breaking scenario, respectively, we analyze experimental constraints on the parameter space. The sparticle spectrum and some phenomenological predictions are also given. Received: 9 June 1999 / Revised version: 12 July 2000 / Published online: 27 November 2000     

Supersymmetry for Fermion Masses

It is proposed that supersymmetry （SUSY） may be used to understand fermion mass hierarchies. A family symmetry ZSL is introduced, which is the cyclic symmetry among the three generation SU（2） doublets. SUSY breaks at a high energy scale - 10^11 GeV. The electroweak energy scale- 100 GeV is unnaturally small No additional global symmetry, like the R-parlty, is imposed. The Yukawa couplings and R-parity violating couplings all take their natural values, which are О（10^0 -10^-2）. Under the family symmetry, only the third generation charged ferrnions get their masses. This family symmetry is broken in the soft SUSY breaking terms, which result in a hierarchical pattern of the fermion masses. It turns out that for the charged leptons, the r mass is from the Higgs vacuum expectation value （VEV） and the sneutrino VEVs, the muon mass is due to the sneutrino VEVs, and the electron gains its mass due to both ZZL and SUSY hreaking. The large neutrino mixing are produced with neutralinos playing the partial role of right-handed neutrinos. │Ve3│, which is for Ve-Vr mixing, is expected to be about 0.1. For the quarks, the third generation masses are from the Higgs VEVs, the second generation masses are from quantum corrections, and the down quark mass due to the sneutrino VEVs. It explains me/ms, ms/me, md 〉 mu and so on. Other aspects of the model are discussed.     

Low scale direct gauge mediation with perturbatively stable vacuum

In a class of direct gauge mediation with a perturbatively stable SUSY breaking vacuum, gaugino masses vanish at the leading order of SUSY breaking F-term. We study the allowed parameter space of the gauge mediation models. By imposing a Tevatron bound on the lightest chargino mass \( {m_{\tilde \chi_1^\pm }} \gtrsim 270\;{\text{eV}} \) and a warm dark-matter mass bound on the light gravitino mass m _3/2 ? 16 eV, we find that almost all the parameter space is excluded. Near future experiments may completely exclude, or possibly discover, the scenario.     

Soft supersymmetry breaking, scalar top-charm mixing and Higgs signatures

The squark mass-matrix from the soft supersymmetry (SUSY) breaking sector contains a rich flavor-mixing structure that allows O(1) mixings among top- and charm-squarks while being consistent with all the existing theoretical and experimental bounds. We formulate a minimal flavor-changing-neutral current scheme in which the squark mixings arise from the non-diagonal scalar trilinear interactions. This feature can be realized in a class of new models with a horizontal U(1)_H symmetry which generates realistic quark-mass matrices and provides a solution to the SUSY μ-problem. Finally, without using the mass-insertion approximation, we analyze SUSY radiative corrections to the H^±bc and h⁰tc couplings, and show that these couplings can reveal exciting new discovery channels for the Higgs boson signals at the Tevatron and the LHC.     

Measuring gauge-mediated supersymmetry breaking parameters at a 500 GeV e^+e^- linear collider

We consider the phenomenology of a class of gauge-mediated supersymmetry (SUSY) breaking (GMSB) models at a Linear Collider (LC) with up to 500 GeV. In particular, we refer to a high-luminosity ( cm s) machine, and use detailed simulation tools for a proposed detector. Among the GMSB-model building options, we define a simple framework and outline its predictions at the LC, under the assumption that no SUSY signal is detected at LEP or Tevatron. We assess the potential of the LC to distinguish between the various SUSY model options and to measure the underlying parameters with high precision, including for those scenarios where a clear SUSY signal would have already been detected at the LHC before starting the LC operations. Our focus is on the case where a neutralino () is the next-to-lightest SUSY particle (NLSP), for which we determine the relevant regions of the GMSB parameter space. Many observables are calculated and discussed, including production cross sections, NLSP decay widths, branching ratios and distributions, for dominant and rare channels. We sketch how to extract the messenger and electroweak scale model parameters from a spectrum measured via, e.g. threshold-scanning techniques. Several experimental methods to measure the NLSP mass and lifetime are proposed and simulated in detail. We show that these methods can cover most of the lifetime range allowed by perturbativity requirements and suggested by cosmology in GMSB models. Also, they are relevant for any general low-energy SUSY breaking scenario. Values of as short as 10's of m and as long as 10's of m can be measured with errors at the level of 10% or better after one year of LC running with high luminosity. We discuss how to determine a narrow range () for the fundamental SUSY breaking scale , based on the measured , . Finally, we suggest how to optimise the LC detector performance for this purpose. Received: 19 May 1999 / Published online: 8 December 1999     

NMSSM from alternative deflection in generalized deflected anomaly mediated SUSY breaking

We propose a new approach to generate messenger–matter interactions in deflected anomaly mediated SUSY breaking mechanism from typical holomorphic messenger–matter mixing terms in the Kahler potential. This approach is a unique feature of AMSB and has no analog in GMSB-type scenarios. New coupling strengths from the scaling of the (already known) Yukawa couplings always appear in this approach. With messenger–matter interactions in deflected AMSB, we can generate a realistic soft SUSY breaking spectrum for next-to-minimal supersymmetric standard model (NMSSM). Successful electroweak symmetry breaking conditions, which is not easy to satisfy in NMSSM for ordinary AMSB-type scenario, can be satisfied in a large portion of parameter space in our scenarios. We study the relevant phenomenology for scenarios with (Bino-like) neutralino and axino LSP, respectively. In the case of axino LSP, the SUSY contributions to \(\Delta a_\mu \) can possibly account for the muon \(g-2\) discrepancy. The corresponding gluino masses, which are found to below 2.2 TeV, could be tested soon at LHC.     

Hard and soft supersymmetry breaking for 'graphinos' in uniform magnetic fields

Using irreducible and reducible representations of the Dirac matrices, we study the two- and four-component quantum mechanical supersymmetric (SUSY) theories for ultrarelativistic fermions in .2 C 1/ dimensions ('graphinos') in a background uniform magnetic field perpendicular to their plane of motion. We then consider ordinary and parity-violating mass terms and identify the former as a soft SUSY breaking term and the latter as the hard SUSY breaking one.     

MSSM curvaton in the gauge-mediated SUSY breaking

We study the curvaton scenario using the MSSM flat directions in the gauge-mediated SUSY breaking model. We find that the fluctuations in the both radial and phase directions can be responsible for the density perturbations in the universe through the curvaton mechanism. Although it has been considered difficult to have a successful curvaton scenario with the use of those flat directions, it is overcome by taking account of the finite temperature effects, which induce a negative thermal logarithmic term in the effective potential of the flat direction.     

二维超对称模型的超对称破缺和Witten指数

构造了一类超势W=(1/n)gφⁿ的二维O(N)对称超对称模型,详细计算了此类模型的Witten指数△。结果表明,当n为偶数时,超对称一定不能破缺,而当n为奇数时,超对称可以破缺。利用大N展开法,还研究了上述模型的超对称自发破缺机制,同时给出了相应的粒子谱。 关键词：     

SUSY Confinement

In response to the present status that searching for SUSY particles has been unsuccessful, we propose a bold scenario that SUSY particles are confined inside hadrons with a required condition of P_R=1 in analog to the color confinement for quarks. The scenario seems to be able to reconcile the beautiful SUSY theory and non-observation at present experiments. On other aspects, some loopholes in the proposal emerge and require to be answered in the future research.     

Flavour violation in supersymmetric theories

We investigate in detail the question of lepton-flavour violation in a SU(2) × U(1) supersymmetric model, where the breaking of supersymmetry (SUSY) is achieved through the coupling to N = 1 supergravity. It is shown that in the limit of degenerate neutrino masses, lepton flavour is exactly conserved. Allowing for neutrino masses compatible with present experimental limits, we analyse SUSY contributions to several lepton-flavour violating processes, comparing the size of these contributions with those already present in the standard Glashow-Salam-Weinberg model. In the case of μ → eγ, SUSY leads to a branching ratio two or three orders of magnitude larger than the corresponding branching ratio in the standard model, for gravitino and photino masses compatible with the experimental limits on the muon anomalous magnetic moment. In contrast, SUSY contributions to are always small, of the order of 10⁻² of the corresponding amplitudes in the standard model, if the gravitino and photino masses are constrained by the K_L − K_S mass difference.     

Minimal gaugomaly mediation

Mixed anomaly and gauge mediation (“gaugomaly” mediation) gives a natural solution to the SUSY flavor problem with a conventional LSP dark matter candidate. We present a minimal version of gaugomaly mediation where the messenger masses arise directly from anomaly mediation, automatically generating a messenger scale of order 50 TeV. We also describe a simple relaxation mechanism that gives rise to realistic μ and Bμ terms. B is naturally dominated by the anomaly-mediated contribution from top loops, so the μ-Bμ sector only depends on a single new parameter. In the minimal version of this scenario the full SUSY spectrum is determined by two continuous parameters (the anomaly-and gauge-mediated SUSY breaking masses) and one discrete parameter (the number of messengers). We show that these simple models can give realistic spectra with viable dark matter.     

Supersymmetric penguin contributions to the decay b\rightarrow s\gamma with non-universal squarks masses

We give explicit expressions for the amplitudes associated with the supersymmetric (SUSY) contributions to the process in the context of SUSY extensions of the standard model (SM) with non-universal soft SUSY breaking terms. From experimental data we deduce limits on the squark mass insertions obtained from different contributions (gluinos, neutralinos and charginos). Received: 20 April 2001 / Revised version: 14 December 2001 / Published online: 5 April 2002     

Metastable SUSY Breaking – Predicting the Fate of the Universe

The possibility that supersymmetry (SUSY) could be broken in a metastable vacuum has recently attracted renewed interest. In these proceedings we will argue that metastability is an attractive and testable scenario. The recent developments were triggered by the presentation of a simple and calculable model of metastable SUSY breaking by Intriligator, Seiberg and Shih (ISS), which we will briefly review. One of the main questions raised by metastability is, why did the universe end up in this vacuum. Using the ISS model as an example we will argue that in a large class of models the universe is automatically driven into the metastable state during the early hot phase and gets trapped there. This makes metastability a natural option from the cosmological point of view. However, it may be more than that. The phenomenologically required gaugino masses require the breaking of R-symmetry. However, in scenarios with a low supersymmetry breaking scale, e.g., gauge mediation a powerful theorem due to Nelson and Seiberg places this at odds with supersymmetry breaking in a truely stable state and metstability becomes (nearly) inevitable. Turning around one can now experimentally test whether gauge mediation is realised in nature thereby automatically testing the possibility of a metastability of the vacuum. Indeed, already the LHC may give us crucial information about the stability of the vacuum.     

Searches for Gauge-Mediated Supersymmetry Breaking topologies in e^+e^- collisions at centre-of-mass energies up to \sqrt{s}=209 \mathrm{GeV}

Searches were performed for topologies predicted by gauge-mediated supersymmetry breaking models (GMSB). All possible lifetimes of the next-to-lightest SUSY particle (NLSP), either the lightest neutralino or slepton, decaying into the lightest SUSY particle, the gravitino, were considered. No evidence for GMSB signatures was found in the OPAL data sample collected at centre-of-mass energies up to $\sqrt{s}=209 \mathrm{GeV}$ at LEP. Limits on the product of the production cross-sections and branching fractions are presented for all search topologies. To test the impact of the searches, a complete scan over the parameters of the minimal model of GMSB was performed. NLSP masses below $53.5 \mathrm{GeV}/c^2$ in the neutralino NLSP scenario, below $87.4 \mathrm{GeV}/c^2$ in the stau NLSP scenario and below $91.9 \mathrm{GeV}/c^2$ in the slepton co-NLSP scenario are excluded at 95% confidence level for all NLSP lifetimes. The scan determines constraints on the universal SUSY mass scale Λ from the direct SUSY particle searches of Λ>40, 27, 21, 17, $15 \mathrm{GeV}/c^2$ for messenger indices N=1,2,3,4,5 for all NLSP lifetimes.     

Runaway Directions in O'Raifeartaigh Models

R-symmetries, which are needed for supersymmetry (SUSY) breaking in O’Raifeartaigh models, often lead to SUSY runaway directions trough a complexified R-transformation. Non-R symmetries also lead to runaway directions in a similar way. This work investigates the occurrence of runaway directions of both SUSY and SUSY breaking types. We clarify previous issues on fractional charges and genericness, and make a refined statement on conditions for runaway directions related to either R-symmetries or non-R symmetries. We present a generic and anomaly-free model to show the existence of runaway directions related to non-R symmetries. We also comment on the possibility to combine the non-R symmetry case to the R-symmetry case by an R-charge redefinition.     

Fixed point and anomaly mediation in partial N=2 supersymmetric standard models

Motivated by the simple toroidal compactification of extra-dimensional SUSY theories, we investigate a partial N =2 supersymmetric(SUSY) extension of the standard model which has an N =2 SUSY sector and an N =1 SUSY sector. We point out that below the scale of the partial breaking of N = 2 to N = 1, the ratio of Yukawa to gauge couplings embedded in the original N =2 gauge interaction in the N =2 sector becomes greater due to a fixed point. Since at the partial breaking scale the sfermion masses in the N = 2 sector are suppressed due to the N = 2 non-renormalization theorem, the anomaly mediation effect becomes important. If dominant, the anomaly-induced masses for the sfermions in the N = 2 sector are almost UV-insensitive due to the fixed point. Interestingly, these masses are always positive, i.e. there is no tachyonic slepton problem. From an example model, we show interesting phenomena differing from ordinary MSSM. In particular, the dark matter particle can be a sbino, i.e. the scalar component of the N = 2 vector multiplet of U(1)_Y. To obtain the correct dark matter abundance, the mass of the sbino, as well as the MSSM sparticles in the N =2 sector which have a typical mass pattern of anomaly mediation, is required to be small. Therefore, this scenario can be tested and confirmed in the LHC and may be further confirmed by the measurement of the N = 2 Yukawa couplings in future colliders. This model can explain dark matter, the muon g-2 anomaly, and gauge coupling unification, and relaxes some ordinary problems within the MSSM. It is also compatible with thermal leptogenesis.     

SUSY Confinement

In response to the present status that searching for SUSY particles has been unsuccessful, we propose a bold scenario that SUSY particles are confined inside hadrons with a required condition of PR = 1 in analog to the color confinement for quarks. The scenario seems to be able to reconcile the beautiful SUSY theory and non-observation at present experiments. On other aspects, some loopholes in the proposal emerge and require to be answered in the future research.     

Search for supersymmetry with gauge-mediated breaking in diphoton events at D0

We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb(-1) of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-to-lightest SUSY particle.     

Higgs Boson with Mass around 125 GeV in SUSY Extensions of the SM

Physics of Atomic Nuclei - The presence of the 125-GeV Higgs boson in the particle spectrum of the minimal supersymmetric (SUSY) standard model (MSSM) implies that the SUSY breaking scale has to be...