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Wan Young Song

Publications and source records attributed to Wan Young Song.

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Threshold corrections to m_b and the b\bar{b} -> H^0_i production in CP-violating SUSY scenarios

The inclusion of supersymmetric threshold corrections to the $b$-quark mass has dramatic consequences in scenarios with large CP-mixing effects in the Higgs sector. In particular, when the phase of the combination $M_{\tilde{g}}μ$ is $\sim 180^{\rm o} \pm 30^{\rm o}$, the lightest-sbottom squark becomes tachyonic and, possibly, the $b$-quark Yukawa coupling nonperturbative for values of $\tan β$ ranging from intermediate up to large or very large, depending on the size of $arg(A_tμ)$, $arg(A_bμ)$, and the details of the spectrum. For these scenarios, when allowed, as well as scenarios with different values of $arg(M_{\tilde{g}}μ)$, the cross sections for the production of the three neutral-Higgs bosons through $b$-quark have rather interesting dependences on $arg(A_tμ)$ and $arg(A_bμ)$, and the deviations induced by the $m_b$ corrections are rather large. In general, such production channel cannot be neglected with respect to the production through gluon fusion. For large CP-mixing effects, the lightest neutral-Higgs boson can be mainly CP odd and the $b$-quark fusion becomes its main production mechanism. Searches at the Tevatron and the LHC can easily detect such a Higgs boson, or constrain the CP-violating scenarios that allow it.

hep-ph

Flavor Hierarchy from Extra Dimension and Gauge Threshold Correction

Dynamical quasi-localization of matter fields in extra dimension is an elegant mechanism to generate hierarchical 4-dimensional Yukawa couplings. We point out that a bulk matter field whose zero mode is quasi-localized can give a large Kaluza-Klein threshold correction to low energy gauge couplings, which is generically of the order of ln (Yukawa)/8pi^2, so it can significantly affect gauge coupling unification. We compute such threshold corrections in generic 5-dimensional theories compactified on S^1/Z_2 X Z_2, and apply the result to grand unified theories on orbifold generating small Yukawa couplings through quasi-localization.

hep-ph

SUSY breaking mediation mechanisms and (g-2)_μ, B -> X_s γ, B -> X_{s} l^+ l^- and B_s -> μ^+ μ^-

We show that there are qualitative differences in correlations among $(g-2)_μ$, $B\to X_s γ$, $B \to X_{s} l^+ l^-$ and $B_s \to μ^+ μ^-$ in various SUSY breaking mediation mechanisms: minimal supergravity (mSUGRA), gauge mediation (GMSB), anomaly mediation (AMSB), gaugino mediation ($\tilde{g}$MSB), weakly and strongly interacting string theories, and $D$ brane models. After imposing the direct search limits on the Higgs boson and SUSY particle search limits and $B\to X_s γ$ branching ratio, we find all the scenarios can accommodate the $a_μ\equiv (g-2)_μ/2 $ in the range of (a few tens)$\times 10^{-10}$, and predict that the branching ratio for $B\to X_s l^+ l^-$ can differ from the standard model (SM) prediction by $\pm 20 %$ but no more. On the other hand, the $B_s \to μ^+ μ^-$ is sensitive to the SUSY breaking mediation mechanisms through the pseudoscalar and stop masses ($m_A$ and $m_{\tilde{t}_1}$), and the stop mixing angle. In the GMSB with a small messenger number, the AMSB, the $\tilde{g}$MSB and the noscale scenarios, one finds that $B(B_s \to μ^+ μ^-) \lesssim 2 \times 10^{-8}$, which is below the search limit at the Tevatron Run II. Only the mSUGRA or string inspired models can generate a large branching ratio for this decay.

hep-ph

Implications on SUSY breaking mediation mechanisms from observing $B_s \to μ^+ μ^-$ and the muon $(g-2)$

We consider $B_s \to μ^+ μ^-$ and the muon $(g-2)_μ$ in various SUSY breaking mediation mechanisms. If the decay $B_s \to μ^+ μ^-$ is observed at Tevatron Run II with a branching ratio larger than $\sim 2 \times 10^{-8} $, the noscale supergravity (including the gaugino mediation), the gauge mediation scenario with small number of messenger fields and low messenger scale, and a class of anomaly mediation scenarios will be excluded, even if they can accommodate a large muon $(g-2)_μ$. On the other hand, the minimal supergravity scenario and similar mechanisms derived from string models can accommodate this observation.

hep-ph

B-decays at Large $\tanβ$ as a Probe of SUSY Breaking

We consider $B_s \to μ^+ μ^-$ and the muon $(g-2)_μ$ in various SUSY breaking mediation mechanisms. If the decay $B_s \to μ^+ μ^-$ is observed at Tevatron Run II with a branching ratio larger than $\sim 2 \times 10^{-8} $, the noscale supergravity (including the gaugino mediation), the gauge mediation scenario with small number of messenger fields and low messenger scale, and a class of anomaly mediation scenarios will be excluded, even if they can accommodate a large muon $(g-2)_μ$. On the other hand, the minimal supergravity scenario and similar mechanisms derived from string models can accommodate this observation.

hep-ph

Operator Analysis of Neutrinoless Double Beta Decay

We study the effective operators of the standard model fields which would yield an observable rate of neutrinoless double beta decay. We particularly focus on the possibility that neutrinoless double beta decay is dominantly induced by lepton-number-violating higher dimensional operators other than the Majorana neutrino mass. Our analysis can be applied to models in which neutrinoless double beta decay is induced either by a strong dynamics or by quantum gravity effects at a fundamental scale near the TeV scale as well as the conventional models in which neutrinoless double beta decay is induced by perturbative renormalizable interactions.

hep-ph

Probing anomalous right-handed top quark couplings in rare B decays

We explore the anomalous right-handed $\bar{t}sW$ and $\bar{t}bW$ couplings using $ B \to X_s γ$ and $B \to X_s l^+ l^-$ decays induced by the flavour-changing penguin diagrams. The anomalous $\bar{t}sW$ coupling can yield 10% enhancement of the $B \to X_s l^+ l^-$ decay rate under the constraint from the present $B \to X_s γ$ data, while it does not affect the forward-backward asymmetry of the charged lepton. The allowed region for anomalous $\bar{t}bW$ coupling by the $ B \to X_s γ$ constraint is two-fold, the small value region and the large value region. Though the effect of the small anomalous coupling on the $B \to X_s l^+ l^-$ branching ratio is very little, it can yield a substantial chanhge for the forward-backward asymmetry.

hep-ph

Sneutrino-Antisneutrino Mixing and Neutrino Mass in Anomaly--mediated Supersymmetry Breaking Scenario

In supersymmetric models with nonzero Majorana neutrino mass, the sneutrino and antisneutrino mix, which may lead to same sign dilepton signals in future collider experiments. We point out that the anomaly-mediated supersymmetry breaking scenario has a good potential to provide an observable rate of such signals for the neutrino masses suggested by the atmospheric and solar neutrino oscillations. The sneutrino mixing rate is naturally enhanced by m_{3/2}/m_{\tildeν}={\cal O}(4π/α) while the sneutrino decay rate is small enough on a sizable portion of the parameter space. We point out also that the sneutrino-antisneutrino mixing can provide much stronger information on some combinations of the neutrino masses and mixing angles than neutrino experiments.

hep-ph

Bi-maximal neutrino mixing and small U_{e3} from Abelian flavor symmetry

Atmospheric neutrino data strongly suggests a near-maximal ν_μ-ν_τ mixing and also solar neutrino data can be nicely explained by another near-maximal ν_e-ν_μ or ν_e-ν_τ mixing. We examine the possibility that this bi-maximal mixing of atmospheric and solar neutrinos arises naturally, while keeping U_{e3} and Δm^2_{sol}/Δm^2_{atm} small enough, as a consequence of Abelian flavor symmetry. Two simple scenarios of Abelian flavor symmetry within supersymmetric framework are considered to obtain the desired form of the neutrino mass matrix and the charged lepton mass matrix parameterized by the Cabibbo angle λ\approx 0.2. Future experiments at a neutrino factory measuring the size of U_{e3} and the sign of Δm^2_{32} could discriminate those scenarios as they predict distinctive values of U_{e3} in connection with Δm^2_{sol}/Δm^2_{atm} and also with the order of the neutrino mass eigenvalues.

hep-ph

Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment

Motivated by the recently measured muon's anomalous magnetic moment $a_μ$, we examine the supersymmetry contribution to $a_μ$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_μ$ allowed by other experimental constraints, e.g. b --> sγand the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_μ$ within the $2σ$ bound. In many other models, b --> sγfavors $a^{SUSY}_μ$ smaller than either the $-1σ$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).

hep-ph