Yukawa Coupling Unification in Supersymmetric Models

We present an updated assessment of the viability of t-b-tau Yukawa coupling unification in supersymmetric models. For the superpotential Higgs mass parameter mu>0, we find unification to less than 1% is possible, but only for GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m_{H_u}^2<m_{H_d}^2. Viable solutions lead to a radiatively generated inverted scalar mass hierarchy, with third generation and Higgs scalars being lighter than other sfermions. These models have very heavy sfermions, so that unwanted flavor changing and CP violating SUSY processes are suppressed, but may suffer from some fine-tuning requirements. While the generated spectra satisfy b->s gamma and (g-2)_mu constraints, there exists tension with the dark matter relic density unless m_{16}<3 TeV. These models offer prospects for a SUSY discovery at the Fermilab Tevatron collider via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino pair production. If mu<0, Yukawa coupling unification to less than 5% can occur for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified models with b->s gamma, (g-2)_mu, and relic density all imply very large values of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection of sparticles may be a challenge even at the LHC.Comment: 38 pages, 15 figures. Fig.15 changed, some references were added. A copy of the paper with better resolution figures can be found at http://www.hep.fsu.edu/~balazs/Physics/Papers/2003

Model Independent Approach to Focus Point Supersymmetry: from Dark Matter to Collider Searches

The focus point region of supersymmetric models is compelling in that it simultaneously features low fine-tuning, provides a decoupling solution to the SUSY flavor and CP problems, suppresses proton decay rates and can accommodate the WMAP measured cold dark matter (DM) relic density through a mixed bino-higgsino dark matter particle. We present the focus point region in terms of a weak scale parameterization, which allows for a relatively model independent compilation of phenomenological constraints and prospects. We present direct and indirect neutralino dark matter detection rates for two different halo density profiles, and show that prospects for direct DM detection and indirect detection via neutrino telescopes such as IceCube and anti-deuteron searches by GAPS are especially promising. We also present LHC reach prospects via gluino and squark cascade decay searches, and also via clean trilepton signatures arising from chargino-neutralino production. Both methods provide a reach out to m_{\tg}\sim 1.7 TeV. At a TeV-scale linear e^+e^- collider (LC), the maximal reach is attained in the \tz_1\tz_2 or \tz_1\tz_3 channels. In the DM allowed region of parameter space, a \sqrt{s}=0.5 TeV LC has a reach which is comparable to that of the LHC. However, the reach of a 1 TeV LC extends out to m_{\tg}\sim 3.5 TeV.Comment: 34 pages plus 36 eps figure

Probing Neutralino Resonance Annihilation via Indirect Detection of Dark Matter

The lightest neutralino of R-parity conserving supersymmetric models serves as a compelling candidate to account for the presence of cold dark matter in the universe. In the minimal supergravity (mSUGRA) model, a relic density can be found in accord with recent WMAP data for large values of the parameter $\tan\beta$, where neutralino annihilation in the early universe occurs via the broad s-channel resonance of the pseudoscalar Higgs boson $A$. We map out rates for indirect detection of neutralinos via 1. detection of neutrinos arising from neutralino annihilation in the core of the earth or sun and 2. detection of gamma rays, antiprotons and positrons arising from neutralino annihilation in the galactic halo. If indeed $A$-resonance annihilation is the main sink for neutralinos in the early universe, then signals may occur in the gamma ray, antiproton and positron channels, while a signal in the neutrino channel would likely be absent. This is in contrast to the hyperbolic branch/focus point (HB/FP) region where {\it all} indirect detection signals are likely to occur, and also in contrast to the stau co-annihilation region, where {\it none} of the indirect signals are likely to occur.Comment: 12 pages including 4 eps figure

Partial wave treatment of Supersymmetric Dark Matter in the presence of CP - violation

We present an improved partial wave analysis of the dominant LSP annihilation channel to a fermion-antifermion pair which avoids the non-relativistic expansion being therefore applicable near thresholds and poles. The method we develop allows of contributions of any partial wave in the total angular momentum J in contrast to partial wave analyses in terms of the orbital angular momentum L of the initial state, which is usually truncated to p-waves, and yields very accurate results. The method is formulated in such a way as to allow easy handling of CP-violating phases residing in supersymmetric parameters. We apply this refined partial wave technique in order to calculate the neutralino relic density in the constrained MSSM (CMSSM) in the presence of CP-violating terms occurring in the Higgs - mixing parameter \mu and trilinear A coupling for large tanb. The inclusion of CP-violating phases in mu and A does not upset significantly the picture and the annihilation of the LSP's to a b b_bar, through Higgs exchange, is still the dominant mechanism in obtaining cosmologically acceptable neutralino relic densities in regions far from the stau-coannihilation and the `focus point'. Significant changes can occur if we allow for phases in the gaugino masses and in particular the gluino mass.Comment: 23 pages LaTeX, 10 eps figures, version to appear in PR

Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter

In supersymmetric models with non-universal gaugino masses, it is possible to have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the gaugino eigenstates experience little mixing so that the lightest SUSY particle remains either pure bino or pure wino. The neutralino relic density can only be brought into accord with the WMAP measured value when bino-wino co-annihilation (BWCA) acts to enhance the dark matter annihilation rate. We map out parameter space regions and mass spectra which are characteristic of the BWCA scenario. Direct and indirect dark matter detection rates are shown to be typically very low. At collider experiments, the BWCA scenario is typified by a small mass gap m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays of \tilde Z_2 are not allowed. However, in this case the second lightest neutralino has an enhanced loop decay branching fraction to photons. While the photonic neutralino decay signature looks difficult to extract at the Fermilab Tevatron, it should lead to distinctive events at the CERN LHC and at a linear e^+e^- collider.Comment: 44 pages, 21 figure