No abstract

Models of natural supersymmetry seek to solve the little hierarchy problem by positing a spectrum of light higgsinos 200 − 300 GeV and light top squarks 600 GeV along with very heavy squarks and TeV-scale gluinos. Such models have low electroweak fine-tuning and satisfy the LHC constraints. However, in the context of the MSSM, they predict too low a value of m h , are frequently in conflict with the measured b → sγ branching fraction and the relic density of thermally produced higgsino-like WIMPs falls well below dark matter (DM) measurements. We propose a framework dubbed radiative natural SUSY (RNS) which can be realized within the MSSM (avoiding the addition of extra exotic matter) and which maintains features such as gauge coupling unification and radiative electroweak symmetry breaking. The RNS model can be generated from SUSY GUT type models with nonuniversal Higgs masses (NUHM). Allowing for high scale soft SUSY breaking Higgs mass m Hu > m 0 leads to automatic cancellations during renormalization group (RG) running, and to radiatively-induced low fine-tuning at the electroweak scale. Coupled with large mixing in the top squark sector, RNS allows for fine-tuning at the 3-10% level with TeV-scale top squarks and a 125 GeV light Higgs scalar h. The model allows for at least a partial solution to the SUSY flavor, CP and gravitino problems since first/second generation scalars (and the gravitino) may exist in the 10-30 TeV regime. We outline some possible signatures for RNS at the LHC such as the appearance of low invariant mass opposite-sign isolated dileptons from gluino cascade decays. The smoking gun signature for RNS is the appearance of light higgsinos at a linear e + e − collider. If the strong CP problem is solved by the Peccei-Quinn mechanism, then RNS naturally accommodates mixed axion-higgsino cold dark matter, where the light higgsino-like WIMPS -which in this case make up only a fraction of the measured relic abundance -should be detectable at upcoming WIMP detectors.

Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.4

We use ISAJET to perform a detailed study of the multilepton signals expected from cascade decays of supersymmetric particle produced at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the regions of parameter space where jets plus missing energy plus 1, 2 (opposite sign and same-sign dileptons), and 3 isolated lepton events should be visible above standard model backgrounds. We find that if any E / T signal at the LHC is to be attributed to gluino and/or squark production, and if mg < ∼ 1 TeV, then several of these signals must be simultaneously observable. Furthermore, assuming 10 fb −1 of integrated luminosity, we find that the reach for supersymmetry in the 1ℓ + jets + E / T channel extends to mg ∼ 2300 (1600) GeV for mq ∼ mg (mq ∼ 1.5mg), and exceeds the corresponding reach in the 0ℓ + E / T channel. We show that measurements of the various topological cross sections, jet and B-hadron multiplicities in these events, together with the charge asymmetry for single lepton and samesign dilepton events, and flavor asymmetry for opposite sign dilepton events, serve to narrow the allowed range of underlying SUGRA parameter values. We also delineate parameter regions where signals with clean isolated dilepton (from slepton production) and trilepton events (from chargino/neutralino production) are visible at the LHC, and examine the extent to which these signals can be separated from other SUSY sources.