SUSY Contributions Research Articles

$B^0 -\overline{B^0}$ mixing, $B\rightarrow J/\psi K_s$ and $B\rightarrow X_d \gamma$ in general MSSM

We consider the gluino-mediated SUSY contributions to B0 - B0 bar mixing, B -> J/psi K_S and B -> X_d gamma in the mass insertion approximation. We find the LL mixing parameter can be as large as |delta_{13}^d_{LL}| < 2*10^-1, but the LR mixing is strongly constrained by the B -> X_d gamma branching ratio and we find |delta_{13}^d_{LR}| < 10^-2. The implications for the direct CP asymmetry in B -> X_d gamma and the dilepton charge asymmetry (A_{ll}) are also discussed, where substantial deviations from the standard model predictions are possible.

CP violations in the K and B meson systems in the SUSY models with (S3)3flavor symmetry

Rare decays of B and K mesons and CP violations thereof are considered in SUSY models with S_3^3 flavor symmetry. SUSY contributions to epsilon_K and epsilon'/epsilon_K can be large, but not to B0 - B0 bar mixing because of strong constraint from B -> X_d gamma for (delta^d_{13})_{LR}. Still large deviations from the SM predictions are possible in the branching ratio for B -> X_d gamma and direct CP violations therein, even if the KM angle gamma is in the range preferred by the SM CKM fit. Experimental study of B -> X_d gamma is strongly recommended as a probe for new physics with nontrivial flavor structure in the (13) mixing.

Yukawa unification in SO(10)

In simple SO(10) SUSY GUTs the top, bottom and tau Yukawa couplings unify at the GUT scale. A naive renormalization group analysis, neglecting weak scale threshold corrections, leads to moderate agreement with the low energy data. However, it is known that intrinsically large threshold corrections proportional to $\mathrm{tan}\ensuremath{\beta}\ensuremath{\sim}{m}_{t}{(M}_{Z}{)/m}_{b}{(M}_{Z})\ensuremath{\sim}50$ can nullify these t, b, \ensuremath{\tau} mass predictions. In this paper we turn the argument around. Instead of predicting fermion masses, we use the constraint of Yukawa unification and the observed values ${M}_{t},$ ${m}_{b}{(m}_{b}),$ ${M}_{\ensuremath{\tau}}$ to constrain SUSY parameter space. We find a narrow region survives for $\ensuremath{\mu}&gt;0$ with $\ensuremath{\mu},$ ${M}_{1/2}\ensuremath{\ll}{m}_{16},$ ${A}_{0}\ensuremath{\approx}\ensuremath{-}1.9{m}_{16}$ and ${m}_{16}&gt;1200 \mathrm{GeV}.$ Demanding Yukawa unification thus makes definite predictions for Higgs boson and sparticle masses. In particular, we find a light Higgs boson with a mass ${m}_{h}^{0}=114\ifmmode\pm\else\textpm\fi{}5\ifmmode\pm\else\textpm\fi{}3 \mathrm{GeV}$ and a light top squark with ${(m}_{{t}_{1}}{)}_{\mathrm{MIN}}\ensuremath{\sim}450 \mathrm{GeV}$ and ${m}_{{t}_{1}}\ensuremath{\ll}{m}_{{b}_{1}}.$ In addition, we find a light chargino and a neutralino LSP. It is also significant that in this region of parameter space the SUSY contribution to the muon anomalous magnetic moment ${a}_{\ensuremath{\mu}}^{\mathrm{SUSY}}&lt;16\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}.$

Bd– [formula omitted] mixing and the Bd→ J/ ψKs asymmetry in general SUSY models

We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B d – B d mixing and to the CP asymmetry a J/ ψK s in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

Bottom-tau unification in a supersymmetric SU(5) grand unified theory and constraints fromb→sγand muong−2

An analysis is made on bottom-tau Yukawa unification in supersymmetric (SUSY) SU(5) grand unified theory (GUT) in the framework of minimal supergravity, in which the parameter space is restricted by some experimental constraints including $\mathrm{Br}(\stackrel{\ensuremath{\rightarrow}}{b}s\ensuremath{\gamma})$ and muon $g\ensuremath{-}2.$ The bottom-tau unification can be accommodated to the measured branching ratio $\mathrm{Br}(\stackrel{\ensuremath{\rightarrow}}{b}s\ensuremath{\gamma})$ if superparticle masses are relatively heavy and the Higgsino mass parameter $\ensuremath{\mu}$ is negative. On the other hand, if we take the latest muon $g\ensuremath{-}2$ data to require positive SUSY contributions, then wrong-sign threshold corrections at the SUSY scale upset the Yukawa unification with more than $20%$ discrepancy. It has to be compensated by superheavy threshold corrections around the GUT scale, which constrains models of flavor in SUSY GUT. A pattern of the superparticle masses preferred by the three requirements is also commented upon.

On the B→Xll decays in general supersymmetric models

We analyze the inclusive semileptonic decays B -> X_s l^+ l^- in the framework of the supersymmetric standard model with non-universal soft-breaking terms at GUT scale. We show that the general trend of universal and non-universal models is a decreasing of branching ratio (BR) and increasing of energy asymmetry (AS). However, only non--universal models can have chances to get very large enhancements in BR and AS, corresponding to large (negative) SUSY contributions to the b -> s \gamma amplitude.

Alternative approach to s\gamma$"&gt;b→sγ in the uMSSM

The gluino contributions to the $C'_{7,8}$ Wilson coefficients for $b->s \gamma$ are calculated within the unconstrained MSSM. New stringent bounds on the $\delta^{RL}_{23}$ and $\delta^{RR}_{23}$ mass insertion parameters are obtained in the limit in which the SM and SUSY contributions to $C_{7,8}$ approximately cancel. Such a cancellation can plausibly appear within several classes of SUSY breaking models in which the trilinear couplings exhibit a factorized structure proportional to the Yukawa matrices. Assuming this cancellation takes place, we perform an analysis of the $b->s \gamma$ decay. We show that in a supersymmetric world such an alternative is reasonable and it is possible to saturate the $b->s \gamma$ branching ratio and produce a CP asymmetry of up to 20%, from only the gluino contribution to $C'_{7,8}$ coefficients. Using photon polarization a LR asymmetry can be defined that in principle allows for the $C_{7,8}$ and $C'_{7,8}$ contributions to the $b->s \gamma$ decay to be disentangled. In this scenario no constraints on the ``sign of $\mu$'' can be derived.

Solving the strongCPand the supersymmetry phase problems with parity symmetry

We propose a simultaneous solution to the strong $\mathrm{CP}$ problem and the supersymmetry (SUSY) phase problem based on parity symmetry realized when the supersymmetric standard model is embedded into a left-right symmetric framework at a scale near $2\ifmmode\times\else\texttimes\fi{}{10}^{16} \mathrm{GeV},$ as suggested by neutrino masses and gauge coupling unification. In this class of models, owing to parity, SUSY contributions to the muon anomalous magnetic moment can be naturally large without conflicting with the electric dipole moments (EDM's) of the electron and the neutron. The strong CP-violation parameter $\overline{\ensuremath{\theta}}$ is zero at the tree level, also due to parity $(P),$ but is induced due to P-violating effects below the unification scale. We estimate the induced $\overline{\ensuremath{\theta}}$ to be $&lt;~{10}^{\ensuremath{-}16},$ if we adopt a constrained supersymmetric spectrum with universal scalar masses. In the more general SUSY-breaking scenario, after imposing flavor changing constraints, we find $\overline{\ensuremath{\theta}}\ensuremath{\sim}{(10}^{\ensuremath{-}8}\ensuremath{-}{10}^{\ensuremath{-}10}),$ which is compatible with, but not much below, the present limit on the neutron EDM. We also argue that potential nonperturbative corrections to $\overline{\ensuremath{\theta}}$ from quantum gravitational effects are not excessive in these models.

Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in supersymmetric grand unified theory with right-handed neutrinos

Motivated by the large mixing angle solutions for the atmospheric and solar neutrino anomalies, flavor changing neutral current processes and lepton flavor violating processes as well as the muon anomalous magnetic moment are analyzed in the framework of SU(5) supersymmetric grand unified theory (SUSY GUT) with right-handed neutrinos. In order to explain realistic mass relations for quarks and leptons, we take into account the effects of higher dimensional operators above the GUT scale. It is shown that the supersymmetric contributions to the $\mathrm{CP}$ violation parameter in ${K}^{0}\ensuremath{-}{K}^{0}$ mixing, ${\ensuremath{\varepsilon}}_{K},$ the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ branching ratio, and the muon anomalous magnetic moment become large in a wide range of parameter space. We also investigate the correlations among these quantities. Within the current experimental bound of $B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}),$ large SUSY contributions are possible either in the muon anomalous magnetic moment or in ${\ensuremath{\varepsilon}}_{K}.$ In the former case, the favorable value of the recent muon anomalous magnetic moment measurement at the BNL E821 experiment can be accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa phase can be different from the prediction within the standard model (SM) and therefore measurements of the $\mathrm{CP}$ asymmetry of the $\stackrel{\ensuremath{\rightarrow}}{B}J/\ensuremath{\psi}{K}_{S}$ mode and $\ensuremath{\Delta}{m}_{{B}_{s}}$ could discriminate this case from the SM. We also show that the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}\ensuremath{\gamma}$ branching ratio can be close to the current experimental upper bound and the mixing induced $\mathrm{CP}$ asymmetry of the radiative B decay can be enhanced in the case where the neutrino parameters correspond to the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.

General flavor blind minimal supersymmetric standard model andCPviolation

We study the implications on flavor changing neutral current and CP violating processes in the context of supersymmetric theories without a new flavor structure (flavor blind supersymmetry). The low energy parameters are determined by the running of the soft breaking terms from the grand unified scale with SUSY phases consistent with the EDM constraints. We find that the CP asymmetry in b --> s gamma can reach large values potentially measurable at B factories, especially in the low BR(b --> s gamma) region. We perform a fit of the unitarity triangle including all the relevant observables. In this case, no sizeable deviations from the SM expectations are found. Finally we analyze the SUSY contributions to the anomalous magnetic moment of the muon pointing out its impact on the b --> s gamma CP asymmetry and on the SUSY spectrum including chargino and stop masses.

Analysis of neutral Higgs-boson contributions to the decaysBs→l+l−andB¯→Kl+l−

We report on a calculation of Higgs-boson contributions to the decays B_s -> l^+l^- and B -> K l^+l^- (l=e, mu) which are governed by the effective Hamiltonian describing b -> s l^+ l^-. Compact formulae for the Wilson coefficients are provided in the context of the type-II two-Higgs-doublet model (2HDM) and supersymmetry (SUSY) with minimal flavour violation, focusing on the case of large tan(beta). We derive, in a model-independent way, constraints on Higgs-boson-mediated interactions, using present experimental results on rare B decays including b -> s gamma, B_s -> mu^+ mu^-, and B -> K^(*) mu^+ mu^-. In particular, we assess the impact of possible scalar and pseudoscalar interactions transcending the standard model (SM) on the branching ratio of B_s -> mu^+ mu^- and the forward-backward (FB) asymmetry of mu^- in B -> K mu^+ mu^- decay. We find that the average FB asymmetry, which is unobservably small within the SM, and therefore a potentially valuable tool to search for new physics, is predicted to be no greater than 4% for a nominal branching ratio of about 6x10^{-7}. Moreover, striking effects on the decay spectrum of B -> K mu^+ mu^- are already ruled out by experimental data on the B_s -> mu^+ mu^- branching fraction. In addition, we study the constraints on the parameter space of the 2HDM and SUSY with minimal flavour violation. While the type-II 2HDM does not give any sizable contributions to the above decay modes, we find that SUSY contributions obeying the constraint on b -> s gamma can affect significantly the branching ratio of B_s -> mu^+ mu^-. We also comment on previous calculations contained in the literature.

High energy behavior ofγγ→ff¯processes in the standard model and minimal supersymmetric standard model

We compute the leading logarithms electroweak contributions to gamma gamma to f f(bar) processes in SM and MSSM. Several interesting properties are pointed out, such as the importance of the angular dependent terms, of the Yukawa terms, and especially of the $\tan^2\beta$ dependence in the SUSY contributions. These properties are complementary to those found in e+e- to f f(bar). These radiative correction effects should be largely observable at future high energy gamma gamma colliders. Polarized beams would bring interesting checks of the structure of the one loop corrections. We finally discuss the need for two-loop calculations and resummation.

Bounds on supersymmetric flavour violating parameters from B→Xsγ

We investigate the constraints on the flavour violating parameters from the decay B→Xsγ, taking into account the interplay of the various sources of flavour violation in the unconstrained MSSM. We present a systematic leading logarithmic QCD analysis of these model-independent constraints, including contributions from gluinos, neutralinos, charginos, charged Higgs bosons and interferences between them. We show that two simple combinations of elements of the down squark mass matrix are stringently bounded over large parts of the parameter space where only weak assumptions on the hierarchical structure of the squark mass matrices are made. We also briefly analyse up to which values SUSY contributions, compatible with B→Xsγ, can enhance the Wilson coefficient C8(mW), which plays an important role in the phenomenology of charmless hadronic B decays.

Gluino–squark contributions to CP violations in the kaon system

Recently it was shown, within the mass insertion approximation (MIA), that the gluino mediated flavor changing neutral current (FCNC) interactions can saturate both epsilon_K and Re(epsilon'/epsilon_K) even for the real Cabibbo-Kobayashi-Maskawa (CKM) matrix through a single CP violating parameter (delta^d_12)_LL. In this work, we extend our previous analysis to the nonvanishing KM phase, and to the effective SUSY model where the MIA is no longer a good approximation. In our model, epsilon_K and B0 - B0 bar mixing can receive significant SUSY contributions. Therefore the usual constraints on rho and eta in the Wolfenstein parametrization of the CKM matrix can be relaxed except for the |V_ub/V_cb| from the semileptonic b -> u transition. This affects K -> pi nu nu bar and K_L -> mu+ mu- indirectly, even if they are not directly induced by gluino-mediated FCNC, while K_L -> pi0 e+ e- is influenced both directly and indirectly. Differences between our model and other SUSY models enhancing Re(epsilon'/epsilon_K) are discussed in detail.

Supersymmetric model contributions to $B^0_d$ – $\bar B^0_d$ mixing and $B\to\pi\pi, \rho\gamma$ decays

Recent results from Belle and BaBar Collaborations hint at a small $\sin2\phi_1$, while the measured $B\to\pi\pi$ rate also seems to be on the low side. Supersymmetric (SUSY) models with down squark mixings can account for the deficits in both cases. By studying the origin of SUSY contributions that could impact on $B^0_d$--$\bar B^0_d$ mixing and $B\to\pi\pi$ decay, we find that the former would most likely arise from left-left or right-right squark mixings, while the latter would come from left-right squark mixings. These two processes in general are not much correlated in the Minimum Supersymmetric Standard Model. If the smallness of $B\to\pi\pi$ is due to SUSY models, one would likely have large $B\to\rho\gamma$ from chiral enhancement, and the rate could be within present experimental reach. Even if $B\to\rho\gamma$ is not greatly enhanced, it could have large mixing dependent CP violation.

Rare K and B decays in the standard model and supersymmetry

We discuss rare decays as probes of physics beyond the Standard Model. After quickly reviewing the SM predictions for rare K and B decays, we discuss SUSY contributions to these processes in two extreme scenarios: the MSSM with minimal flavour and CP violation, and the most general minimal SUSY extension of the SM. We stress how rare decays are in principle able to discriminate between various scenarios of new physics.

Recent result from E821 experiment on muon g−2 and unconstrained minimal supersymmetric Standard Model

Recently, the E821 experiment at the Brookhaven National Laboratory announced their latest result of their muon g−2 measurement which is about 2.6- σ away from the standard model prediction. Taking this result seriously, we examine the possibility to explain this discrepancy by the supersymmetric contribution. Our analysis is performed in the framework of the unconstrained supersymmetric standard model which has free seven parameters relevant to muon g−2. We found that, in the case of large tan β, sparticle masses are allowed to be large in the region where the SUSY contribution to the muon g−2 is large enough, and hence the conventional SUSY search may fail even at the LHC. On the contrary, to explain the discrepancy in the case of small tan β, we found that (i) sleptons and SU(2) L gauginos should be light, and (ii) negative search for the Higgs boson severely constrains the model in the framework of the mSUGRA and gauge-mediated model.

ε′/ε and rare K decays in the standard model and supersymmetry

After briefly reviewing the status of ε′/ε in the Standard Model, I discuss SUSY contributions to ε′/ε, K + → π + νν, K L → π 0 νν and K L → π 0 e + e -. While in the simplest case of the MSSM with Minimal Flavour Violation the main effect is a suppression of these transitions with respect to the Standard Model, large enhancements are possible in more general SUSY models, with interesting correlations among the different processes.

Electric dipole moment andCPviolation inB→Xsl+l−in supergravity models with nonuniversal gaugino masses

The constraints of electric dipole moments (EDMs) of the electron and neutron on parameter space in supergravity (SUGRA) models with nonuniversal gaugino masses are analyzed. It is shown that, with a light sparticle spectrum, a sufficient cancellation in the calculation of EDMs can happen for all phases of order 1 in the small $\mathrm{tan}\ensuremath{\beta}$ case and all phases but ${\ensuremath{\varphi}}_{\ensuremath{\mu}}$ $(|{\ensuremath{\varphi}}_{\ensuremath{\mu}}|\ensuremath{\lesssim}\ensuremath{\pi}/6)$ of order 1 in the large $\mathrm{tan}\ensuremath{\beta}$ case. This is in contrast with the case of MSUGRA in which, in the parameter space where cancellations among various SUSY contributions to EDMs happen, $|{\ensuremath{\varphi}}_{\ensuremath{\mu}}|$ must be less than $\ensuremath{\pi}/10$ for small $\mathrm{tan}\ensuremath{\beta}$ and $\mathcal{O}{(10}^{\ensuremath{-}2})$ for large $\mathrm{tan}\ensuremath{\beta}.$ Direct $\mathrm{CP}$ asymmetries and the T-odd normal polarization of the lepton in $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ are investigated in these models. In the large $\mathrm{tan}\ensuremath{\beta}$ case, ${A}_{\mathrm{CP}}^{2}$ and ${P}_{N}$ for $l=\ensuremath{\mu}$ $(\ensuremath{\tau})$ can be enhanced by about a factor of 10 (10) and 10 (3), respectively, compared to those of MSUGRA.

Effects of CP-violating phases on Higgs boson production at hadron colliders in the Minimal Supersymmetric Standard Model

If the soft Supersymmetry (SUSY) breaking masses and couplings are complex, then the associated CP-violating phases can in principle modify the known phenomenological pattern of the Minimal Supersymmetric Standard Model (MSSM). We investigate here their effects on Higgs boson production in the gluon–gluon fusion mode at the Tevatron and the Large Hadron Collider (LHC), by taking into account all experimental bounds available at present. The by far most stringent ones are those derived from the measurements of the Electric Dipole Moments (EDMs) of fermions. However, it has recently been suggested that, over a sizable portion of the MSSM parameter space, cancellations among the SUSY contributions to the EDMs can take place, so that the CP-violating phases can evade those limits. We find a strong dependence of the production rates of any neutral Higgs state upon the complex masses and couplings over such parts of the MSSM parameter space. We show these effects relatively to the ordinary MSSM rates as well as illustrate them at absolute cross section level at both colliders.