P. Ohmann

Supersymmetric Grand Unified Theories: Two Loop Evolution of Gauge and Yukawa Couplings

We make a numerical study of guage and Yukawa unification in supersymmetric grand unified models and examine the quantitative implications of fermion mass [ital Ansa]

Supersymmetric particle spectrum

[ital iuml]---[ital tze] at the grand unified scale. Integrating the renormalization group equations with [alpha][sub 1]([ital M][sub [ital Z]]) and [alpha][sub 2]([ital M][sub [ital Z]]) as inputs, we find [alpha][sub 3]([ital M][sub [ital Z]])[congruent]0.111(0.122) for [ital M][sub SUSY]=[ital m][sub [ital t]] and [alpha][sub 3]([ital M][sub [ital Z]])[congruent]0.106(0.116) for [ital M][sub SUSY]=1 TeV at one-loop (two-loop) order. Including [ital b] and [tau] Yukawa couplings in the evolution, we find an upper limit of [ital m][sub [ital t]][approx lt]200 GeV from Yukawa unification. For given [ital m][sub [ital t]][approx lt]175 GeV, there are two solutions for [beta]: one with tan[beta][gt][ital m][sub [ital t]]/[ital m][sub [ital b]], and one with sin[beta][congruent]0.78([ital m][sub [ital t]]/150 GeV). Taking a popular [ital Ansatz] for the mass matrices at the unified scale, we obtain a lower limit on the top-quark mass of [ital m][sub [ital t]][approx gt]150(115) GeV for [alpha][sub 3]([ital M][sub [ital Z]])=0.11(0.12) and an upper limit on the supersymmetry parameter tan[beta][approx lt]50 if [alpha][sub 3]([ital M][sub [ital Z]])=0.11. The evolution of the quark mixing elements is also evaluated.

Phenomenological implications of the mt RGE fixed point for SUSY Higgs boson searches

We examine the spectrum of supersymmetric particles predicted by grand unified theoretical (GUT) models where the electroweak symmetry breaking is accomplished radiatively. We evolve the soft-supersymmetry-breaking parameters according to the renormalization group equations (RGE). The minimization of the Higgs potential is conveniently described by means of tadpole diagrams. We present complete one-loop expressions for these minimization conditions, including contributions from the matter and the gauge sectors. We concentrate on the low tan[beta] fixed point region (that provides a natural explanation of a large top quark mass) for which we find solutions to the RGE satisfying both experimental bounds and fine-tuning criteria. We also find that the constraint from the consideration of the lightest supersymmetric particle as the dark matter of the Univerese is accommodated in much of parameter space where the lightest neutralino is predominantly gaugino. The supersymmetric mass spectrum displays correlations that are model independent over much of the GUT parameter space.

Universal evolution of Cabibbo-Kobayashi-Maskawa matrix elements

Abstract In minimal SUSY-GUT models with MSUSY ≲ 1 TeV, the renormalization group equations have a solution dominated by the infrared fixed point of the top Yukawa coupling. This fixed point predicts mt = (200 GeV) sin β; combined with the LEP results it excludes mt ≲ 130 GeV. For mt in the range 130–160 GeV, we discuss the sensitivity of the mt fixed point result to GUT threshold corrections and point out the implications for Higgs boson searches. The lightest scalar h has mass 60–85 GeV and will be detectable at LEP II. At SSC/LHC, each of the five scalars h, H, A, H± may be detectable, but not all of them together; in one parameter region none will be detectable.

Constraints on SUSY GUT unification from b ---> s gamma decay

We derive the two-loop evolution equations for the Cabibbo-Kobayashi-Maskawa matrix. We show that to leading order in the mass and CKM hierarchies the scaling of the mixings |V ub | 2 , |V cb | 2 , |V td | 2 , |V ts | 2 and of the rephase-invariant CP-violating parameter J is universal to all orders in perturbation theory. In leading order the other CKM elements do not scale. Imposing the constraint λ b = λ τ at the GUT scale determines the CKM scaling factor to be ≃ 0.58 in the MSSM. The weak interaction quark eigenstates and the quark mass eigenstates differ in the Standard Model as described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix. In this paper we show that the scaling of the CKM matrix follows a universal pattern to leading order in the mass and CKM hierarchies; namely, the CKM mixing elements that involve the third generation and CP violation scale together, while the other components of the CKM matrix do not scale to leading order. This makes it much simpler to consider the form of the quark mixings at any other scale, in particular at the scale of a grand unified theory (GUT). The common scaling is a model-independent feature of the evolution, but the amount of scaling can vary between theories.

Constraints on supersymmetric grand unification from [ital b][r arrow][ital s][gamma] decay

The top-quark Yukawa infrared fixed-point solution of the renormalization group equations, with minimal supersymmetry and GUT unification, defines a low-energy spectrum of supersymmetric particle masses in terms of a few GUT-scale parameters assuming universal boundary conditions. We give predictions in this model for the inclusive

Implications of Supersymmetric Grand Unification

b\to s\gamma

Multilepton SUSY signals from R-parity violation at the Fermilab Tevatron.

branching fraction and investigate the impact of non-universal scalar mass boundary conditions. We find our results do not depend significantly on the value of the GUT-scale trilinear coupling

Supergravity Solutions in the Low-

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\tan\beta

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