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Register a new userDeviations from universality of slepton masses in the MSSM
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M. Gomez-Bock
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In this paper we propose an ansatz that applies to the slepton mass matrices. In our approach these matrices contain a dominant sector that can be diagonalized exactly. We study the numerical results for the slepton mass eigenstates, looking for deviations from universality, which is usually assumed when one evaluates the production of sleptons at future colliders.
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Supersymmetric theories supplemented by an underlying flavor-symmetry $mathcal{G}_f$ provide a rich playground for model building aimed at explaining the flavor structure of the Standard Model. In the case where supersymmetry breaking is mediated by gravity, the soft-breaking Lagrangian typically exhibits large tree-level flavor violating effects, even if it stems from an ultraviolet flavor-conserving origin. Building on previous work, we continue our phenomenological analysis of these models with a particular emphasis on leptonic flavor observables. We consider three representative models which aim to explain the flavor structure of the lepton sector, with symmetry groups $mathcal{G}_f = Delta(27)$, $A_4,$ and $S_3$.
In supersymmetric theory, the sfermion-fermion-gaugino interactions conserve the chirality of (s)fermions. The effect appears as the charge asymmetry in $m(jl)$ distributions at the CERN Large Hadron Collider where jets and leptons arise from the cascade decay $tilde{q} to q tilde{chi}^0_2 to qltilde{l}$. Furthermore, the decay branching ratios and the charge asymmetries in $m(jl)$ distributions are flavor non-universal due to the $tilde{l}_L$ and $tilde{l}_R$ mixing. When $tanbeta$ is large, the non-universality between $e$ and $mu$ becomes $O(10)%$ level. We perform a Monte Carlo simulation for some minimal supergravity benchmark points to demonstrate the detectability.
There are many models with non-universal soft SUSY breaking sfermion mass parameters at the grand unification scale. Even in the mSUGRA model scalar mass unification might occur at a scale closer to M_Planck, and renormalization effects would cause a mass splitting at M_GUT. We identify an experimentally measurable quantity Delta that correlates strongly with delta m^2 = m^2_{selectron_R}(M_GUT) - m^2_{selectron_L}(M_GUT), and which can be measured at electron-positron colliders provided both selectrons and the chargino are kinematically accessible. We show that if these sparticle masses can be measured with a precision of 1% at a 500 GeV linear collider, the resulting precision in the determination of Delta may allow experiments to distinguish between scalar mass unification at the GUT scale from the corresponding unification at Q ~ M_Planck. Experimental determination of Delta would also provide a distinction between the mSUGRA model and the recently proposed gaugino-mediation model. Moreover, a measurement of Delta (or a related quantity Delta) would allow for a direct determination of delta m^2.
In a supersymmetric model, the presence of a right handed neutrino with a large Yukawa coupling $f_{ u}$ would affect slepton masses via its contribution to the renormalization group evolution between the grand unification and weak scales. Assuming a hierarchichal pattern of neutrino masses, these effects are large for only the third generation of sleptons. We construct mass combinations to isolate the effect of $f_{ u}$ from mass corrections already expected from tau Yukawa couplings. We then analyze the size of these effects, assuming that the Super-Kamiokande data constrain 0.033 eV $alt m_{ u_{tau}} alt 0.1$ eV and that neutrino masses arise via a see-saw mechanism. We also explore whether these effects might be detectable in experiments at future $e^+e^-$ linear colliders. We find that $m_{tnu_{tau}}$ needs to be measured with a precision of about 2-3% to measure the effect of $f_{ u}$ if the neutrino and top Yukawa couplings unify at the grand unification scale. In a simple case study, we find a precision of only 6-10% might be attainable after several years of operation. If the neutrino Yukawa coupling is larger, or in more complicated models of neutrino masses, a determination of $ttau_1$ and $tnu_{tau}$ masses might provide a signal of a Yukawa interaction of neutrinos.
We consider a five-dimensional Minimal Supersymmetric Standard Model compactified on a S1/Z2 orbifold, and study the evolution of neutrino masses, mixing angles and phases for different values of tan beta and different radii of compactification. We consider the usual four dimensional Minimal Supersymmetric Standard Model limit plus two extra-dimensional scenarios: where all matter superfields can propagate in the bulk, and where they are constrained to the brane. We discuss in both cases the evolution of the mass spectrum, the implications for the mixing angles and the phases. We find that a large variation for the Dirac phase is possible, which makes models predicting maximal leptonic CP violation especially appealing.
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