Takeo Moroi

Focus points and naturalness in supersymmetry

We analyze focus points in supersymmetric theories, where a parameters renormalization group trajectories meet for a family of ultraviolet boundary conditions. We show that in a class of models including minimal supergravity, the up-type Higgs mass parameter has a focus point at the weak scale, where its value is highly insensitive to the universal scalar mass. As a result, scalar masses as large as 2 to 3 TeV are consistent with naturalness, and all squarks, sleptons and heavy Higgs scalars may be beyond the discovery reaches of the CERN Large Hadron Collider and proposed linear colliders. Gaugino and Higgsino masses are, however, still constrained to be near the weak scale. The focus point behavior is remarkably robust, holding for both moderate and large tan {beta}, any weak scale gaugino masses and A parameters, variations in the top quark mass within experimental bounds, and for large variations in the boundary condition scale. (c) 2000 The American Physical Society.

Wino cold dark matter from anomaly mediated SUSY breaking

Abstract The cosmological moduli problem is discussed in the framework of sequestered sector/anomaly mediated supersymmetry (SUSY) breaking. In this scheme, the gravitino mass (corresponding to the moduli masses) is naturally 10–100 TeV, and hence the lifetime of the moduli fields can be shorter than ∼1 sec. As a result, the cosmological moduli fields should decay before big-bang nucleosynthesis starts. Furthermore, in the anomaly mediated scenario, the lightest superparticle (LSP) is the Wino-like neutralino. Although the large annihilation cross section means the thermal relic density of the Wino LSP is too small to be the dominant component of cold dark matter (CDM), moduli decays can produce Winos in sufficient abundance to constitute CDM. If Winos are indeed the dark matter, it will be highly advantageous from the point of view of detection. If the halo density is dominated by the Wino-like LSP, the detection rate of Wino CDM in Ge detectors can be as large as 0.1–0.01 event/kg/day, which is within the reach of the future CDM detection with Ge detector. Furthermore, there is a significant positron signal from pair annihilation of Winos in our galaxy which may give a spectacular signal at AMS.

Multi-TeV Scalars are Natural in Minimal Supergravity

For a top quark mass fixed to its measured value, we find natural regions of minimal supergravity parameter space where all squarks, sleptons, and heavy Higgs scalars have masses far above 1 TeV and are possibly beyond the reach of the Large Hadron Collider at CERN. This result is simply understood in terms of focus point renormalization group behavior and holds in any supergravity theory with a universal scalar mass that is large relative to other supersymmetry breaking parameters. We highlight the importance of the choice of fundamental parameters for this conclusion and for naturalness discussions in general.

Anomaly mediation in supergravity theories

We consider the effects of anomalies on the supersymmetry-breaking parameters in supergravity theories. We construct a supersymmetric expression for the anomaly-induced terms in the 1PI effective action; we use this result to compute the complete one-loop formula for the anomaly-induced gaugino mass. The mass receives contributions from the super-Weyl, Kahler, and sigma-model anomalies of the supergravity theory. We point out that the anomaly-mediated gaugino mass can be affected by local counterterms that cancel the super-Weyl-Kahler anomaly. This implies that the gaugino mass cannot be predicted unless the full high-energy theory is known.

Discovering Supersymmetry at the Tevatron in W -ino Lightest Supersymmetric Particle Scenarios

In supersymmetric models, Winos, partners of the SU(2) gauge bosons, may be the lightest supersymmetric particles (LSPs). For generic parameters, charged and neutral Winos are highly degenerate. Charged Winos travel macroscopic distances, but can decay to neutral Winos and extremely soft leptons or pions before reaching the muon chambers, thereby circumventing conventional trigger requirements based on energetic decay products or muon chamber hits. However, these charginos are detectable, and can be triggered on when produced in association with jets. In addition, we propose a new trigger for events with a high pT track and low hadronic activity. For Tevatron Run II with luminosity 2 fb−1, the proposed searches can discover Winos with masses up to 300 GeV and explore a substantial portion of the parameter space in sequestered sector models [1]. Typeset using REVTEX

Supernatural supersymmetry: Phenomenological implications of anomaly mediated supersymmetry breaking

We discuss the phenomenology of supersymmetric models in which supersymmetry breaking terms are induced by the super-Weyl anomaly. Such a scenario is envisioned to arise when supersymmetry breaking takes place in another world, i.e., on another brane. We review the anomaly-mediated framework and study in detail the minimal anomaly-mediated model parametrized by only 3+1 parameters: M{sub aux}, m{sub 0}, tan {beta}, and sgn({mu}). The renormalization group equations exhibit a novel focus point (as opposed to fixed point) behavior, which allows squark and slepton masses far above their usual naturalness bounds. We present the superparticle spectrum and highlight several implications for high energy colliders. Three lightest supersymmetric particle (LSP) candidates exist: the W-ino, the stau, and the tau sneutrino. For the W-ino LSP scenario, light W-ino triplets with the smallest possible mass splittings are preferred; such W-inos are within reach of run II Fermilab Tevatron searches. Finally, we study a variety of sensitive low energy probes, including b{yields}s{gamma}, the anomalous magnetic moment of the muon, and the electric dipole moments of the electron and neutron. (c) 2000 The American Physical Society.

Cosmology of supersymmetric models with low-energy gauge mediation

We study the cosmology of supersymmetric models in which the supersymmetry-breaking effects are mediated by gauge interactions at about the 10{sup 5} GeV scale. We first point out that the gravitino is likely to overclose the Universe in this class of models. This requires an entropy production, which prefers a baryogenesis mechanism at a relatively low temperature. The Affleck-Dine mechanism for baryogenesis is one of the possibilities to generate enough baryon asymmetry, but the analysis is nontrivial since the shape of the potential for the flat direction differs substantially from the conventional hidden sector case. To see this, we first perform a two-loop calculation to determine the shape of the potential. By combining the potential with the supergravity contribution, we then find that the Affleck-Dine baryogenesis works efficiently to generate sufficient baryon asymmetry. On the other hand, we also point out that string moduli fields, if present, are stable and their coherent oscillations overclose the Universe by more than 15 orders of magnitude. One needs a very late inflationary period with an e-folding of N{approx_gt}5 and an energy density of {approx_lt}(10{sup 7} GeV){sup 4}. A thermal inflation is enough for this purpose. Fortunately, the Affleck-Dine baryogenesis is so efficient thatmorexa0» enough baryon asymmetry can survive the late inflation. {copyright} {ital 1997} {ital The American Physical Society}«xa0less

SNEUTRINO COLD DARK MATTER WITH LEPTON-NUMBER VIOLATION

Abstract The tau sneutrino is proposed as a candidate for galactic halo dark matter, and as the cold dark matter (CDM) component of the universe. A lepton-number-violating sneutrino mass, ν ν , splits the tau sneutrino into two mass eigenstates: ν → ν ± . The absence of a Z ν − ν − coupling implies that the lighter mass eigenstate, ν − , does not annihilate via the s-channel Z-exchange to a low cosmological abundance, and furthermore, halo sneutrinos do not scatter excessively in Ge detectors. For the majority of the relevant parameter space, the event rate in Ge detectors is ≥10−2 events/kg/day. The lepton number violation required for sneutrino CDM implies that the tau neutrino mass is mντ≳5 MeV, large enough to be excluded by B factory experiments. Events of the form l + l − E / or jj E / , with low mll or mjj, may be observed at LEP2. A seesaw mechanism is investigated as the origin for the lepton number violation, and several other cosmological and particle physics consequences of sneutrino CDM are discussed.

Radiative decay of a long-lived particle and big-bang nucleosynthesis

The effects of radiatively decaying, long-lived particles on big-bang nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after BBN, they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between the BBN theory and observation. We calculate the abundances of the light elements, including the effects of photodissociation induced by a radiatively decaying particle, but neglecting the hadronic branching ratio. Using these calculated abundances, we derive a constraint on such particles by comparing our theoretical results with observations. Taking into account the recent controversies regarding the observations of the light-element abundances, we derive constraints for various combinations of the measurements. We also discuss several models which predict such radiatively decaying particles, and we derive constraints on such models. {copyright} {ital 1999} {ital The American Physical Society}

Effects of the right-handed neutrinos on ΔS = 2 and ΔB = 2 processes in supersymmetric SU(5) model

We discuss an extra source of CP and flavor violations in supersymmetric SU(5) grand unified model with the right-handed neutrinos. In such a model, the right-handed down-type squarks tilde{d}_R interact with the right-handed neutrinos above the GUT scale, and the renormalization group effect can generate sizable off-diagonal elements in the mass matrix of tilde{d}_R. Because of new Yukawa phases which exist in the SU(5) model, these off-diagonal elements have, in general, large CP violating phases. The renormalization group induced off-diagonal elements affect the K and B decays. In particular, in this model, supersymmetric contribution to the epsilon_K parameter can be as large as the currently measured experimental value, and hence the effect might be seen as an anomaly in the on-going test of the Cabibbo-Kobayashi-Maskawa triangle.