Diverse experimental constraints now motivate models of supersymmetry breaking in which some superpartners have masses well above the weak scale. Three alternatives are focus point supersymmetry and inverted hierarchy models, which embody a naturalness constraint, and the more recent framework of split supersymmetry, which relaxes that constraint. Many aspects of their phenomenology are very similar. They can be distinguished, however, through detailed study of superoblique parameters, the Higgs potential and other observables. © 2005 Elsevier B.V. All rights reserved.

In recent work, it has been argued that multi-TeV masses for scalar superpartners are not unnatural. Indeed, they appear to have significant phenomenological virtues. Here we explore the implications of such 'focus point' supersymmetry for the dark matter problem. We find that constraints on relic densities do not place upper bounds on neutralino or scalar masses. We demonstrate that, in the specific context of minimal supergravity, a cosmologically stable mixed gaugino-Higgsino state emerges as an excellent, robust dark matter candidate. We estimate that, over a wide range of the unknown parameters, the spin-independent proton-neutralino cross sections fall in the range accessible to planned search experiments. (C) 2000 Elsevier Science B.V.

We modify and extend an earlier proposal by Brown and Teitelboim to relax the effective cosmological term by nucleation of branes coupled to a three-index gauge potential. Microscopic considerations from string/M-theory suggest two major innovations in the framework. First, the dependence of brane properties on the compactification of extra dimensions may generate a very small quantized unit for jumps in the effective cosmological term. Second, internal degrees of freedom for multiply coincident branes may enhance tunneling rates by exponentially large density of states factors. These new features essentially alter the relaxation dynamics. By requiring stability on the scale of the lifetime of the universe, rather than absolute stability, we derive a non-trivial relation between the supersymmetry breaking scale and the value of the cosmological term. It is plausibly, though not certainly, satisfied in Nature.

Dark matter candidates arising in models of particle physics incorporating weak scale supersymmetry may produce detectable signals through their annihilation into neutrinos, photons, or positrons. A large number of relevant experiments are planned or underway. The "logically possible" parameter space is unwieldy. By working in the framework of minimal supergravity, we can survey the implications of the experiments for each other, as well as for direct searches, collider searches, low-energy experiments, and naturalness in a transparent fashion. We find that a wide variety of experiments provide interesting probes. Particularly promising signals arise in the mixed gaugino-Higgsino region. This region is favored by low-energy particle physics constraints and arises naturally from minimal supergravity due to the focus point mechanism. Indirect dark matter searches and traditional particle searches are highly complementary. In cosmologically preferred models, if there are charged superpartners with masses below 250 GeV, then some signature of supersymmetry must appear before the CERN LHC begins operation. ©2001 The American Physical Society.

Neutrinos with energies above 10(8) GeV are expected from cosmic ray interactions with the microwave background and are predicted in many speculative models. Such energetic neutrinos are difficult to detect, as they are shadowed by Earth, but rarely interact in the atmosphere. Here we propose a novel detection strategy: Earth-skimming neutrinos convert to charged leptons that escape Earth, and these leptons are detected in ground level fluorescence detectors. With the existing HiRes detector, neutrinos from some proposed sources are marginally detectable, and improvements of 2 orders of magnitude are possible at the proposed Telescope Array.