Search

We examine arguments that could avoid light superpartners as an implication of supersymmetric radiative electroweak symmetry breaking. We argue that, from the point of view of string theory and standard approaches to generating the mu-term, cancellations among parameters are not a generic feature. While the coefficients relating the Z-mass to parameters in the soft supersymmetry breaking Lagrangian can be made smaller, these same mechanisms lead to lighter superpartner masses at the electroweak scale. Consequently we strengthen the implication that gluinos, neutralinos, and charginos are light and likely to be produced at the Fermilab Tevatron and a linear collider., Comment: 27 pages, 3 figures

We discuss fine-tuning constraints on supergravity models. The tightest constraints come from the experimental mass limits on two key particles: the lightest CP even Higgs boson and the gluino. We also include the lightest chargino which is relevant when universal gaugino masses are assumed. For each of these particles we show how fine-tuning increases with the experimental mass limit, for four types of supergravity model: minimal supergravity, no-scale supergravity (relaxing the universal gaugino mass assumption), D-brane models and anomaly mediated supersymmetry breaking models. Among these models, the D-brane model is less fine tuned.The experimental propects for an early discovery of Higgs and supersymmetry at LEP and the Tevatron are discussed in this framework., 17 pages, Latex, including 5 eps figures

The parameters of the supersymmetry Lagrangian are the place where experiment and theory will meet. We show that measuring them is harder than has been thought, particularly because of large unavoidable dependences on phases. Measurements are only guaranteed if a lepton collider with a polarized beam and sufficient energy to produce the relevant sparticles is available. Current limits on superpartner masses, WIMPs, and the supersymmetric Higgs are not general, and need re-evaluation. We also tentatively define the MRM (Minimum Reasonable Model), whose parameters may be measurable at LEP, FNAL and LHC., 10 pages, 1 figure; a typographical error corrected in eq. (1) and one reference added

There is a class of supersymmetric models which is well-motivated by hints of evidence for SUSY and consistent with all existing data. It is important to study the predictions of these models. They are characterized by M(N3) > M(C1) > M(snu) > M(N1) (where Ni and Ci are neutralino and chargino mass eigenstates), |mu| ~< M1 ~< M2 ~= M(Z), mu < 0, and tan(beta) near 1. Their LEP signatures are mostly unusual. Most produced superpartners are invisible! A good signature is two photons plus large missing energy. There are also excess events at large recoil mass in the single photon plus nothing channel. We list the main signatures for charginos, stops, etc., which are also likely to be unconventional. This class of models will be definitively tested at LEP194 with 100 pb^{-1} per detector, and almost definitively tested at LEP184., 15 pages, revtex, 1 figure (included). We include a paragraph on the improved understanding of the SM background for gamma-gamma-Emiss events that has occurred since our original posting. We also emphasize the softness of the leptons from chargino decays in our models. Our conclusions are unchanged

We find that re-analyzing the LEP/SLC data with light superpartners and low $\alpha_s(\mz^2)\simeq 0.112$ yields a better fit to the data than the Standard Model, giving a satisfactory description of the $R_b$ measurement, and a better fit to $A_{LR}$. A large body of low energy ($q^2 \ll \mz^2$) data and analyses provide compelling evidence for $\alpha_s(\mz^2)\simeq 0.112$. Global fits to LEP/SLC data in the Standard Model, however, converge on a value of $\alpha_s(\mz^2)\simeq 0.126$. Recently it has become increasingly clear that these should be viewed as incompatible rather than values that can be averaged. We investigate the possibility that new physics is causing the LEP high value. To this end we have conducted a global analysis of LEP/SLC data in the Standard Model and also in the Minimal Supersymmetric Standard Model. Several predictions could confirm (or rule out) the results of this paper: light chargino and stop, top decays into stop and neutralino, large $R_b$, large $A_{LR}$, and a higher $M_W$. We briefly discuss the implications of low $\alpha_s$ for more fundamental high-scale supersymmetric theories., Comment: 12 pages, LaTeX. Available via anonymous ftp at ftp://williams.physics.lsa.umich.edu/pub/preprints/UM-TH-95-16.ps

Assuming that the actual values of the top quark mass at FNAL and of the ratio of partial widths Z->bb/Z->hadrons at LEP are within their current one-sigma reported ranges, we present a No-Lose Theorem for superpartner searches at LEP II and an upgraded Tevatron. We impose only two theoretical assumptions: the Lagrangian is that of the Minimal Supersymmetric Standard Model with arbitrary soft-breaking terms, and all couplings remain perturbative up to scales of order 10^16 GeV; there are no assumptions about the soft SUSY breaking parameters, proton decay, cosmology, etc. In particular, if the LEP and FNAL values hold up and supersymmetry is responsible for the discrepancy with the SM prediction of the partial width of Z->bb, then we must have charginos and/or top squarks observable at the upgraded machines. Furthermore, little deviation from the SM is predicted within "super-unified" SUSY. Finally, it appears to be extremely difficult to find any unified MSSM model, regardless of the form of soft SUSY breaking, that can explain the partial width for large tan(beta); in particular, no model with top-bottom-tau Yukawa coupling unification appears to be consistent with the experiments.

We argue that CP--violation effects below a few tenths of a percent are probably undetectable at hadron and electron colliders. Thus only operators whose contributions interfere with tree--level Standard Model amplitudes are detectable. We list these operators for Standard Model external particles and some two and three body final state reactions that could show detectable effects. These could test electroweak baryogenesis scenarios., Comment: 11pp, LaTeX, UM--TH--92--27(massaged to make TeX output cleaner), no pictures

Experiments in progress with hydrogen and deuterium may in practice determine the fundamental parameters and constituents of the weak interaction within the framework of unified gauge theories. In particular, for SU (2) X U(1) theories, from the results of these experiments one can infer the masses of the charged and neutral weak vector bosons (and thus sin20w), and the isospin classification of the right-handed portions of the electron and the u- and d-quarks. Non-singlet assignments for eR, u R and d R would imply the existence of additional leptons and/or quarks. Hydrogen/deuterium data also may be used to discriminate between SU (2) X U (1) models and various models based on larger gauge groups.

We derive the structure functions for massive transverse and longitudinal gauge bosons. The results are checked against perturbation theory for some simple examples. Using these structure functions, it is simple to calculate cross sections for producing heavy quarks or leptons, Higgs bosons, new gauge bosons, or any particles carrying SU(2) quantum numbers, and to estimate the collider predictions of any new model of WW scattering.

Many broken supersymmetric theories contain two light neutral fermions χ, χ′ which are mixtures of supersymmetric partners of the gauge and Higgs bosons. The heavier of these (χ′) can be produced in e+e− annihilation by e+e− → χχ′ or χ′χ′ with cross sections that may be comparable to that for e+e− → νμνμ : σ = (0.1 to 10) pb at √s = 30 GeV. The χ′ likes to decay into an e+e− or μ+μ− pair and a χ, which is likely for cosmological reasons to be almost a pure photino γ Associated production e+e− → χχ′ can lead to a one-sided “zen” event structure with visible decay products in one hemisphere only, while e+e− → χ′χ′ can give 4-lepton final states with missing energy.

For certain ranges of masses of the supersymmetric partners of the gluons, quarks and W-bosons, it is expected that a few events of production and decay of the partners could be observed at the CERN pp collider. The characteristic signatures are events with l± j , l± jj , jjj , jj and j where l ± is an isolated charged lepton, j is a hadron jet and stands for missing p T . Some recently reported events are of this type.

We consider under what conditions any narrow neutral resonance, particularly the recently reported state ξ(2.2), could be a Higgs particle, either a fundamental boson or a composite technicolor state. A number of tests are summarized including what is expected in ϒ decay, b-quark decay, Z 0 decays, branching ratios and properties of ξ(2.2) decay, and production at hadron machines. Implications for the standard model, technicolor, and supersymmetry are discussed.

We discuss some possible processes, mainly decays, to search for flavor-changing neutral currents. We examine the theoretical constraints from present data as well as improved sensitivities which might be achieved in future experiments. We focus on the decays K 0 → μ e, Σ + p μ e, τ → μμ e and μ → eee as being particularly interesting for further experimental searches.

We construct a low energy supergravity model consistent with all cosmological and particle physics constraints, by omitting some of the usual simplifying assumptions in the hidden sector. The model has heavy squarks, light gluinos and a higgsino as the lightest supersymmetric particle. The experimental implications of the model are discussed. In particular, the possibility of detecting photinos in monojet events, and a new way of producing Higgs bosons in e + e − collisions with a good signature, H 0 + missing energy, occur as new results.

We show that one can obtain real parts of scattering amplitudes by knowing the imaginary parts at only nearby energies. This is accomplished by re-casting the dispersion integral into an equivalent form which we will calla “derivative analyticity relation”. Predictions are given for forward amplitudes where σT is measured: pp, p p , K ± p , π ± p , γ p . We deduce the real part of the elastic pp amplitude away from the forward direction at ISR energies.

We extend the analyses of Fayet, and Fayet and Farrar, of experimental searches for gluinos, the supersymmetric partners of gluons. Because of their large production cross sections, present data appears to exclude gluino masses below 3.5−6 GeV/c2 and may be more restrictive. Lifetime considerations give an upper limit on scalar quark masses and on the scale of supersymmetry breaking, and experiments sensitive to missing energy will provide interesting limits on the latter. Since gluinos remain very light in many models, they will either be detected soon or many supersymmetric theories will be excluded.

Motivated by ideas about the structure of high energy amplitudes in impact parameter space, we suggest a simple form (equation six) for the dominant elastic amplitude (Pomeron exchange in Regge language). It is imaginary at t = 0 but has a significant real part away from t = 0 even at very high energies. It is able to describe the experimental features of all elastic scattering to the highest ISR energies, including the increase in slope for − t t t needed in recent work to understand the πN scattering amplitude at 6 GeV/ c in terms of the absorption model; this phase variation cannot be simply parametrized by a Regge pole. Using the Pomeron also solves the long-standing shrinkage problem for the absorption model.

Motivated by specific connections to dark matter signatures, we study the prospects of observing the presence of a relatively light gluino whose mass is in the range ~(500-900) GeV with a wino-like lightest supersymmetric particle with mass in the range of ~(170-210) GeV. The light gaugino spectra studied here is generally different from other models, and in particular those with a wino dominated LSP, in that here the gluinos can be significantly lighter. The positron excess reported by the PAMELA satellite data is accounted for by annihilations of the wino LSP and their relic abundance can generally be brought near the WMAP constraints due to the late decay of a modulus field re-populating the density of relic dark matter. We also mention the recent FERMI photon constraints on annihilating dark matter in this class of models and implications for direct detection experiments including CDMS and XENON. We study these signatures in models of supersymmetry with non-minimal soft breaking terms derived from both string compactifications and related supergravity models which generally lead to non-universal gaugino masses. At the LHC, large event rates from the three-body decays of the gluino in certain parts of the parameter space are found to give rise to early discovery prospects for the gaugino sector. Excess events at the 5 sigma level can arise with luminosity as low as order 100 pb^{-1} at a center of mass energy of 10 TeV and less than ~ 1 fb^{-1} at a center of mass energy of 7 TeV., 2 columns, 9 pages, 5 figure captions

We show that the linear polarization of a gluon emerging from the reaction e + e → e + e + g + g is large - on the order of 20%. This polarization arises from the process γ + γ → quark loop → g + g, which is expected to dominate the two gluon jet cross section. The polarization can be used to test quantum chromodynamics (QCD), even if the gluon jets cannot be distinguished clearly from the background of quark jets. If the QCD prediction is accepted, our result can be used to enhance the signal of gluon jets, thereby aiding in the study of their properties.

We analyze the consequences of the proposal by Glashow that monojet events observed by UA1 are related to a new form of quark matter. We find that this idea requires the production of about 2 e + e − , 2 μ + μ − and 2 γ + hadron events, all at the same large effective for every monojet event explained in this way.