Search

The optimisation of the plasma target design for high quality beam laser-driven plasma injector electron source relies on numerical parametric studies using Particle in Cell (PIC) codes. The common input parameters to explore are laser characteristics and plasma density profiles extracted from computational fluid dynamic studies compatible with experimental measurements of target plasma density profiles. We demonstrate the construction of surrogate models using machine learning technique for a laser-plasma injector (LPI) electron source based on more than 12000 simulations of a laser wakefield acceleration performed for sparsely spaced input parameters [1]. Surrogate models are very interesting for LPI design and optimisation because they are much faster than PIC simulations. We develop and compare the performance of three surrogate models, namely, Gaussian processes (GP), multilayer perceptron (MLP), and decision trees (DT). We then use the best surrogate model to quickly find optimal working points to get a selected electron beam energy, charge and energy spread using different methods, namely random search, Bayesian optimisation and multi-objective Bayesian optimisation, Comment: 10 pages, 13 figures

Exploring new target schemes for laser wakefield accelerators is essential to meet the challenge of increasing repetition rates while ensuring stability and quality of the produced electron beams. The prototyping of a two-chamber gas cell integrated into the beam line and operating in continuous gas flow is introduced and discussed in the frame of ionisation injection. We report the numerical fluid modeling used to assist the density profile shaping. We describe the test bench used for cell prototype assessment, in particular the plasma electron density and longitudinal distribution of species relevant for ionisation injection. The lifetime of the target key part is measured for different materials. Perspectives to high power operation are outlined.

A method for the optimisation and advanced studies of a laser-plasma electron injector is presented, based on a truncated ionisation injection scheme for high quality beam production. The SMILEI code is used with laser envelope approximation and a low number of particles per cell to reach computation time performances enabling the production of a large number of accelerator configurations. The developed and tested workflow is a possible approach for the production of large dataset for laser-plasma accelerator optimisation. A selection of functions of merit used to grade generated electron beams is discussed. Among the significant number of configurations, two specific working points are presented in details. All data generated are left open to the scientific community for further study and optimisation.

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D-brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades., Comment: Summary document for international workshop "Beyond the Standard Model at the LHC" (Pre-SUSY09), Northeastern University, Boston, June 2-4, 2009

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e+e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point., Comment: 17pp; references corrected

In an effort to promote communication between the formal and phenomenological branches of the high-energy theory community, we provide a description of some important issues in supersymmetric and string phenomenology. We describe each within the context of string constructions, illustrating them with specific examples where applicable. Each topic culminates in a set of questions that we believe are amenable to direct consideration by string theorists, and whose answers we think could help connect string theory and phenomenology., Comment: 31 pages

We review and compare theoretically and phenomenologically a number of possible family symmetries, which when combined with unification, could be important in explaining quark, lepton and neutrino masses and mixings, providing new results in several cases. Theoretical possibilities include Abelian or non-Abelian, symmetric or non symmetric Yukawa matrices, Grand Unification or not. Our main focus is on anomaly-free U(1) family symmetry combined with SU(5) unification, although we also discuss other possibilities. We provide a detailed phenomenological fit of the fermion masses and mixings for several examples, and discuss the supersymmetric flavour issues in such theories, including a detailed analysis of lepton flavour violation. We show that it is not possible to quantitatively and decisively discriminate between these different theoretical possibilities at the present time., Comment: 75 pages, 4 figures

String theories in principle address the origin and values of the quark and lepton masses. Perhaps the small values of neutrino masses could be explained generically in string theory even if it is more difficult to calculate individual values, or perhaps some string constructions could be favored by generating small neutrino masses. We examine this issue in the context of the well-known three-family standard-like Z_3 heterotic orbifolds, where the theory is well enough known to construct the corresponding operators allowed by string selection rules, and analyze the D- and F-flatness conditions. Surprisingly, we find that a simple see-saw mechanism does not arise. It is not clear whether this is a property of this construction, or of orbifolds more generally, or of string theory itself. Extended see-saw mechanisms may be allowed; more analysis will be needed to settle that issue. We briefly speculate on their form if allowed and on the possibility of alternatives, such as small Dirac masses and triplet see-saws. The smallness of neutrino masses may be a powerful probe of string constructions in general. We also find further evidence that there are only 20 inequivalent models in this class, which affects the counting of string vacua., Comment: 18 pages in RevTeX format. Single-column postscript version available at http://sage.hep.upenn.edu/~bnelson/singpre.ps

We propose an approach to explaining why naive large quantum fluctuations are not the right estimate for the cosmological constant. We argue that the universe is in a superposition of many vacua, in such a way that the resulting fluctuations are suppressed by level repulsion to a very small value. The approach combines several aspects of string theory and the early history of the universe, and is only valid if several assumptions hold true. The approach may also explain why the effective cosmological constant reamins small as the universe evolves though several phase transitions. It provides a non-anthropic mechansim leading to a small, non-zero cosmological constant., Comment: Talk given at Rencontres de Moriond, 2004 by G.L. Kane

We study the implications for the minimal supersymmetric standard model (MSSM) of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. For each of these cases -- as well as the case that the lightest Higgs eigenstate is at, or slightly above, the current LEP limit -- we provide explicit sample configurations of the Higgs sector as well as the soft supersymmetry breaking Lagrangian parameters necessary to generate these outcomes. We argue that all of the cases seem fine-tuned, with the least fine-tuned outcome being that with Higgs mass near 115 GeV. Seeking to minimize this tuning we investigate ways in which the ``maximal-mixing'' scenario with large top-quark trilinear A-term can be obtained from simple string-inspired supergravity models. We find these obvious approaches lead to heavy gauginos and/or problematic low-energy phenomenology with minimal improvement in fine-tuning., Comment: 24 pages; uses RevTeX

After an introduction recalling the theoretical motivation for low energy (100 GeV to TeV scale) supersymmetry, this review describes the theory and experimental implications of the soft supersymmetry-breaking Lagrangian of the general minimal supersymmetric standard model (MSSM). Extensions to include neutrino masses and nonminimal theories are also discussed. Topics covered include models of supersymmetry breaking, phenomenological constraints from electroweak symmetry breaking, flavor/CP violation, collider searches, and cosmological constraints including dark matter and implications for baryogenesis and inflation., Comment: 273 pages; 35 figures; submitted to Physics Reports

Assuming string theorists will not soon provide a compelling case for the primary theory underlying particle physics, the field will proceed as it has historically: with data stimulating and testing ideas. Ideally the soft supersymmetry breaking Lagrangian will be measured and its patterns will point to the underlying theory. But there are two new problems. First a matter of principle: the theory may be simplest at distance scales and in numbers of dimensions where direct experiments are not possible. Second a practical problem: in the foreseeable future (with mainly hadron collider data) too few observables can be measured to lead to direct connections between experiment and theory. In this paper we discuss and study these issues and consider ways to circumvent the problems, studying models to test methods. We propose a semi-quantitative method for focusing and sharpening thinking when trying to relate incomplete data to incomplete theory, as will probably be necessary., Comment: 43 pages, 1 figure

We argue that in the context of string theory a large number N of connected degenerate vacua that mix will lead to a ground state with much lower energy, essentially because of the standard level repulsion of quantum theory for the wavefunction of the Universe. We imagine a history where initial quantum fluctuations give an energy density $\sim m_{susy}^2m_{Pl}^2$, but the universe quickly cascades to an energy density $\sim m_{susy}^2m_{Pl}^2/N$. Then at various phase transitions there are large contributions to the energy density and rearrangement of levels, followed again by a rapid cascade to the ground state or near it. If this mechanism is correct, the ground state of the theory describing our world would be a superposition of a large number of connected string vacua,with shared superselection sets of properties such as three families etc. The observed value of the cosmological constant in terms of the Planck mass, the scale of supersymmetry breaking and the number of connected string vacua., Comment: 8 pages

Recently it has been understood that flavor-changing processes mediated by Higgs bosons could be a new and powerful tool for discovering supersymmetry. In this paper we show that they may also provide an important method for constraining the parameters of the minimal supersymmetric standard model (MSSM). Specifically, we show that observation of B_s -> mu mu at the Tevatron implies a significant, model-independent lower bound on tan(beta) in the MSSM. This is very important because tan(beta) enters crucially in predictions and interpretations of the MSSM, though it is difficult to measure. Within specific models, or with other data, the bound becomes significantly stronger., Comment: 17 pages Latex, 7 figures

The decay $B_d \to \phi K_S$ is a special probe of physics beyond the Standard Model (SM), since it has no SM tree level contribution. Motivated by recent data suggesting a deviation from the SM for its time-dependent CP asymmetry, we examine supersymmetric explanations. Chirality preserving contributions are generically small, unless gluino is relatively light. Higgs contributions are also too small to explain a large asymmetry. Chirality flipping $LR$ and $RL$ gluino contributions actually can provide sizable effects without conflict with all related results. We discuss how various insertions can be distinguished, and argue the needed sizes of mass insertions are reasonable., Comment: 5 pages, 4 figures. A few typos in the abstract are corrected. This is a shortened version of hep-ph/0212092

We study the implications of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. In the minimal supersymmetric standard model (MSSM) all of these, as well as the cases where the Higgs mass equals or exceeds 115 GeV, seem fine-tuned. We examine some interpretations of the fine tuning in high scale theories. The least fine-tuned MSSM outcome will have a Higgs mass at 115 GeV, while approaches that extend the MSSM at the weak scale can naturally have larger Higgs masses., Comment: Uses RevTeX; references added

The rare decay B --> Phi K_S is a well-known probe of physics beyond the Standard Model because it arises only through loop effects yet has the same time-dependent CP asymmetry as B --> Psi K_S. Motivated by recent data suggesting new physics in B --> Phi K_S, we look to supersymmetry for possible explanations, including contributions mediated by gluino loops and by Higgs bosons. Chirality-preserving LL and RR gluino contributions are generically small, unless gluinos and squarks masses are close to the current lower bounds. Higgs contributions are also too small to explain a large asymmetry if we impose the current upper limit on B(B_s --> mu mu). On the other hand, chirality-flipping LR and RL gluino contributions can provide sizable effects and while remaining consistent with related results in B --> Psi K_S, Delta M_s, B --> X_s gamma and other processes. We discuss how the LR and RL insertions can be distinguished using other observables, and we provide a string-based model and other estimates to show that the needed sizes of mass insertions are reasonable., Comment: 33 pages, 32 figures, Updated version for PRD. Includes discussions of other recent works on this topic. Added discussions & plots for gluino mass dependence and effects of theoretical uncertainties

To make progress in learning the underlying fundamental theory, it will be necessary to combine bottom-up phenomenology and top-down analysis -- in particular, top-down is unlikely to succeed alone. Here I elaborate on the role of both, and describe obstacles that need to be overcome to help data point toward the underlying theory, as well as approaches that might help to bypass full systematic treatments. I also summarize arguments that superpartners are probably being produced at the Tevatron Collider., Comment: Invited Plenary talk, SUSY02, Hamburg, June 2002

Recently published benchmark models have contained rather heavy superpartners. To test the robustness of this result, several benchmark models have been constructed based on theoretically well-motivated approaches, particularly string-based ones. These include variations on anomaly and gauge-mediated models, as well as gravity mediation. The resulting spectra often have light gauginos that are produced in significant quantities at the Tevatron collider, or will be at a 500 GeV linear collider. The signatures also provide interesting challenges for the LHC. In addition, these models usually account for electroweak symmetry breaking with relatively less fine-tuning than previous benchmark models., Comment: 44 pages, 4 figures; some typos corrected. Revisions reflect published version

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 explore supersymmetric Type I string-motivated three-family scenarios in which the Standard Model is embedded within two sets of intersecting D branes with U(1)-extended Pati-Salam gauge groups. We study a model inspired by the Shiu-Tye Type IIB orientifold, in which a three-family scenario is obtained by assuming that the gauge symmetry breaking takes place in two stages; the Pati-Salam group arises from diagonal breaking of the U(N) gauge groups, which is then broken to the SM gauge group. We investigate the diagonal breaking scenario in detail and find that generically there are difficulties involved in decoupling the exotic Higgs remnants. On the phenomenological side, proper low energy gauge coupling predictions effectively lead to a ``single brane'' scenario for M_string of order 10^16 GeV. The soft parameters in this limit are constrained by a well-known sum rule, leading to a distinctive phenomenological pattern for the low energy mass spectrum., Comment: 18 pages

In this talk a number of broad issues are raised about the origins of CP violation and how to test the ideas., Comment: 17 pages, LaTeX, 6 postscript figures. Uses iopart10.clo, iopart12.clo and iopart.cls. Plenary talk given at the BSM Phenomenology Workshop, Durham, UK, 6-11 May 2001. To appear in the proceedings

The gluino contributions to the $C'_{7,8}$ Wilson coefficients for $b->s \gamma$ are calculated within the unconstrained MSSM. New stringent bounds on the $\delta^{RL}_{23}$ and $\delta^{RR}_{23}$ mass insertion parameters are obtained in the limit in which the SM and SUSY contributions to $C_{7,8}$ approximately cancel. Such a cancellation can plausibly appear within several classes of SUSY breaking models in which the trilinear couplings exhibit a factorized structure proportional to the Yukawa matrices. Assuming this cancellation takes place, we perform an analysis of the $b->s \gamma$ decay. We show that in a supersymmetric world such an alternative is reasonable and it is possible to saturate the $b->s \gamma$ branching ratio and produce a CP asymmetry of up to 20%, from only the gluino contribution to $C'_{7,8}$ coefficients. Using photon polarization a LR asymmetry can be defined that in principle allows for the $C_{7,8}$ and $C'_{7,8}$ contributions to the $b->s \gamma$ decay to be disentangled. In this scenario no constraints on the ``sign of $\mu$'' can be derived., Comment: LaTeX2e, 23 pages, 7 ps figure, needs package epsfig

We consider supersymmetric inflation models in which inflation occurs at an intermediate scale and which provide a solution to the $\mu$ problem and the strong CP problem. Such models are particularly attractive since inflation, baryogenesis and the relic abundance of cold dark matter are all related by a set of parameters which also affect particle physics collider phenomena, neutrino masses and the strong CP problem. For such models the natural situation is a universe containing matter composed of baryons, massive neutrinos, lightest superpartner cold dark matter, and axions. The present day relic abundances of these different forms of matter are (in principle) calculable from the supersymmetric inflation model together with a measurement of the CMB temperature and the Hubble constant. From these relic abundances one can deduce the amount of the present day dark energy density., Comment: Version to appear in New Journal of Physics. 19 pages, Latex

Recently the HEAT balloon experiment has confirmed an excess of high-energy positrons in cosmic rays. They could come from annihilation of dark matter in the galactic halo. We discuss expectations for the positron signal in cosmic rays from the lightest superpartner. The simplest interpretations are incompatible with the size and shape of the excess if the relic LSPs evolved from thermal equilbrium. Non-thermal histories can describe a sufficient positron rate. Reproducing the energy spectrum is more challenging, but perhaps possible. The resulting light superpartner spectrum is compatible with collider physics, the muon anomalous magnetic moment, Z-pole electroweak data, and other dark matter searches., Comment: 4 pages, 2 figures, references added, minor wording changes

This is the foreword to the book we edited on the origins and early development of supersymmetry, which has been just issued by World Scientific. This book presents a view on the discovery of supersymmetry and pioneering investigations before summer 1976, mainly in the words of people who participated. It combines anecdotal descriptions and personal reminiscences with more technical summaries of the trailblazers, covering the birth of the theory and its first years -- origin of the idea, four-dimensional field theory realization, and supergravity. The eyewitnesses convey to us the drama of one of the deepest discoveries in theoretical physics in the 20-th century. Contributors: V. Akulov, R. Di Stefano, P. Fayet, S. Ferrara, G.-L. Gervais, N. Koretz-Golfand, E. Likhtman, M. Marinov, A. Neveu, L. O'Raifeartaigh, P. Ramond, B. Sakita, J. Schwarz, M. Sohnius, V. Soroka, J. Strathdee, D. Volkov, J. Wess, P. West., Comment: Latex, 6 pages, no figures

We examine what can be deduced from the discovery of a Higgs boson, focusing on a possible discovery at LEP. The analysis begins with the most general situation where no further constraints can be deduced, and then specializes to include various assumptions. Assuming naturalness, the relatively large mass suggests that one or more of larger $\tan \beta$, large phase, or extra singlets is present. We discuss the implications of a Higgs mass discovery for the SUSY spectrum, and in particular gluinos and stops. We show that a lighter gluino produceable at the Tevatron remains a likely possibility, in disagreement with a recent claim., Comment: Reference added, some other minor changes. 17 pages, Latex

We examine the flavor structure of the trilinear superpotential couplings which can result from embedding the Standard Model within D brane sectors in Type IIB orientifold models, which are examples within the Type I string framework. We find in general that the allowed flavor structures of the Yukawa coupling matrices to leading order are given by basic variations on the "democratic" texture ansatz. In certain interesting cases, the Yukawa couplings have a novel structure in which a single right-handed fermion couples democratically at leading order to three left-handed fermions. We discuss the viability of such a ``single right-handed democracy'' in detail; remarkably, even though there are large mixing angles in the u,d sectors separately, the CKM mixing angles are small. The analysis demonstrates the ways in which the Type I superstring framework can provide a rich setting for investigating novel resolutions to the flavor puzzle., Comment: 23 pages, references added

High-energy data has been accumulating over the last ten years, and it should not be ignored when making decisions about the future experimental program. In particular, we argue that the electroweak data collected at LEP, SLC and Tevatron indicate a light scalar particle with mass less than 500 GeV. This result is based on considering a wide variety of theories including the Standard Model, supersymmetry, large extra dimensions, and composite models. We argue that a high luminosity, 600 GeV e+e- collider would then be the natural choice to feel confident about finding and studying states connected to electroweak symmetry breaking. We also argue from the data that worrying about resonances at multi-TeV energies as the only signal for electroweak symmetry breaking is not as important a discovery issue for the next generation of colliders. Such concerns should perhaps be replaced with more relevant discovery issues such as a Higgs boson that decays invisibly, and ``new physics'' that could conspire with a heavier Higgs boson to accommodate precision electroweak data. An e+e- collider with energy less than about 600 GeV is ideally suited to cover these possibilities., Comment: 20 pages, latex

We study the supersymmetry parameter region excluded if no Higgs is found at LEP, and the region allowed if a Higgs boson is found at LEP. We describe the full seven parameter structure of Higgs sector. When supersymmetry phases are included, $\tan \beta$ greater than or equal to 2 is always allowed, and the lower limit on lightest Higgs mass if no signal is found is about 20% lower than in the Standard Model and about 10% lower than in the MSSM with phases set to 0, $\pi$, Comment: 11 papges, 2 figures

The Beyond the Standard Model Working Group discussed a variety of topics relating to exotic searches at current and future colliders, and the phenomenology of current models beyond the Standard Model. For example, various supersymmetric (SUSY) and extra dimensions search possibilities and constraints are presented. Fine-tuning implications of SUSY searches are derived. The implications of Higgs (non)-discovery are discussed, as well as the program HDECAY. The individual contributions are included seperately. Much of the enclosed work is original, although some is reviewed., Comment: 45 pages, 21 figures, iop style files included, editor: B.C. Allanach. Replacement has typos corrected, refs updated and a clearer fig. 1

We revisit the results of recent electroweak baryogenesis calculations and include all allowed large CP-violating supersymmetric phases. If the phases are large, the resulting baryon asymmetry can be considerably larger than the observed value $n_B/s \sim 4 \times 10^{-11}$. Much of the asymmetry must therefore be washed out, and we argue that the upper bound on the light Higgs mass is larger than the value reported in previous work., Comment: 15 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., Comment: 17 pages, Latex, including 5 eps figures

Once superpartners are discovered at colliders, the next challenge will be to determine the parameters of the supersymmetric Lagrangian. We illustrate how the relative phases of the gluino, SU(2), and U(1) gauginos and the Higgsino mass parameter mu can be measured at a hadron collider without ad hoc assumptions about the underlying physics, focusing on Fermilab. We also discuss how the gluino and LSP masses can be measured., Comment: 19 pages with 5 figures

Recently it has been demonstrated that large phases in softly broken supersymmetric theories are consistent with electric dipole moment constraints, and are motivated in some (Type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework $\epsilon$ and $\epsilon'/\epsilon$ can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. An unconventional flavor structure of the squark mass matrices (with enhanced super-CKM mixing) is required for consistency with B and K system observables., Comment: 9 pages, 1 figure; revised version to appear in Phys.Rev.Lett

We investigate the possibility of large CP- violating phases in the soft breaking terms derived in superstring models. The bounds on the electric dipole moments (EDM's) of the electron and neutron are satisfied through cancellations occuring because of the structure of the string models. Three general classes of four-dimensional string models are considered: (i) orbifold compactifications of perturbative heterotic string theory, (ii) scenarios based on Ho\v{r}ava-Witten theory, and (iii) Type I string models (Type IIB orientifolds). Nonuniversal phases of the gaugino mass parameters greatly facilitate the necessary cancellations among the various contributions to the EDM's; in the overall modulus limit, the gaugino masses are universal at tree level in both the perturbative heterotic models and the Ho\v{r}ava-Witten scenarios, which severely restricts the allowed regions of parameter space. Nonuniversal gaugino masses do arise at one-loop in the heterotic orbifold models, providing for corners of parameter space with ${\cal O}(1)$ phases consistent with the phenomenological bounds. However, there is a possibility of nonuniversal gaugino masses at tree level in the Type I models, depending on the details of the embedding of the SM into the D- brane sectors. We find that in a minimal model with a particular embedding of the Standard Model gauge group into two D- brane sectors, viable large phase solutions can be obtained over a wide range of parameter space., Comment: 28 pages, 6 figures; corrected bug in the code and a few typos, results qualitatively unchanged

We examine the soft supersymmetry breaking parameters that result from various ways of embedding the Standard Model (SM) on D-branes within the Type I string picture, allowing the gaugino masses and $\mu$ to have large CP- violating phases. One embedding naturally provides the relations among soft parameters to satisfy the electron and neutron electric dipole moment constraints even with large phases, while with other embeddings large phases are not allowed. The string models provide some motivation for large phases in the soft breaking parameters. The results generally suggest how low energy data might teach us about Planck scale physics., Comment: 11 pages, 2 eps figures; revised references and updated text

Theories with non-Abelian flavour symmetries lead at zeroth order to neutrino degeneracy and massless charged fermions. The flavour symmetry is spontaneously broken sequentially to give hierarchies $\Delta m_{atm}^2 \gg \Delta m_{\odot}^2$ and $m_\tau \gg m_\mu \gg m_e$, and a misalignment of the vacuum between neutrino and charged sectors gives large $\theta_{atm}$. Explicit models are given which determine $\theta_{atm} = 45^\circ$. A similar construction gives vacuum misalignment for the lighter generations and gives a vanishing $\beta \beta_{0 \nu}$ rate, so that there is no laboratory constraint on the amount of neutrino hot dark matter in the universe, and the solar mixing angle is also maximal, $\theta_\odot = 45^\circ$., Comment: 10 pages

We report the first fully general numerical calculation of the neutron and electron dipole moments, including the seven significant phases. We find that there are major regions in the parameter space where none of the phases are required to be small, contrary to the conventional wisdom. The electric dipole moments (EDM's) do provide useful constraints, allowing other regions of parameter space to be carved away. We keep all superpartner masses light so agreement with experimental limits arises purely from interesting relations among soft breaking parameters., Comment: 23 pages, 7 figures; 2 references added

We analyse the fine-tuning constraints arising from absence of superpartners at LEP, without strong universality assumptions. We show that such constraints do not imply that charginos or neutralinos should have been seen at LEP, contrary to the usual arguments. They do however imply relatively light gluinos $(m_{\tilde g} \lsim 350 GeV)$ and/or a relation between the soft-breaking SU(3) gaugino mass and Higgs soft mass $m_{H_U}$. The LEP limit on the Higgs mass is significant, especially at low $\tan \beta$, and we investigate to what extent this provides evidence for both a lighter gluino and correlations between soft masses., Comment: 22 pages, Latex, including 2 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., Comment: 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., Comment: 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 provide a mini-guide to some of the possible manifestations of weak scale supersymmetry. For each of six scenarios we provide a brief description of the theoretical underpinnings, the adjustable parameters, a qualitative description of the associated phenomenology at future colliders, comments on how to simulate each scenario with existing event generators., Comment: Report of Snowmass Supersymmetry Theory Working Group; 14 pages plus 3 figures using latex2e and snow2e.cls; this version has corrected a number of typos from the first version