SUSY Contributions Research Articles

CP violation in rare semileptonic B decays and supersymmetry

We study the effect of new flavor changing SUSY phases arising in the squark mass matrix in semileptonic decays B→Xsℓ+ℓ−, and B→K(∗)ℓ+ℓ− (ℓ=e,μ). SUSY effects are parametrized using the mass insertion approximation formalism. Constraints on SUSY contributions coming from other processes (e.g. b→sγ, B→K∗ℓ+ℓ−) are taken into account. Chargino and gluino contributions to photon and Z-mediated decays are included and nonperturbative corrections are considered. We study the correlation between the CP (and forward–backward) asymmetries and the expected value of the inclusive branching ratio. Several possible scenarios are distinguished and discussed according to the mass insertion that is considered.

Can flavor-independent supersymmetric soft phases Be the source of all CP violation?

Recently it has been demonstrated that large phases in softly broken supersymmetric (SUSY) theories are consistent with electric dipole moment constraints, and are motivated in some (type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework, epsilon and epsilon(')/epsilon can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. An unconventional flavor structure of the squark mass matrices (with enhanced super-Cabibbo-Kobayashi-Maskawa mixing) is required for consistency with B and K system observables.

CPconserving constraints on supersymmetricCPviolation in the MSSM

We address the following question. Take the Constrained Minimal Supersymmetric Standard Model (CMSSM) with the two CP violating SUSY phases different from zero, and neglect the bound coming from the electric dipole moment of the neutron (EDM): is it possible to fully account for CP violation in the kaon and B systems using only the SUSY contributions with vanishing CKM phase? We show that the ${BR}(B\to X_{s} \gamma)$ constraint, though CP conserving, forces a negative answer to the above question. This implies that, even in the regions of the CMSSM where a cancellation of different contributions to the EDM allows for large SUSY phases, it is not possible to exploit the SUSY phases to fully account for observable CP violation. Hence to have sizeable SUSY contributions to CP violation, one needs new flavor structures in the sfermion mass matrices beyond the usual CKM matrix.

A model independent analysis of B → Xsℓ +ℓ − decays in supersymmetry

Recently the semileptonic decays B a ̊ X se +e −, B a ̊ X sμ +μ − in generic supersymmetric extensions of the Standard Model have been studied in ref. [1]. In this talk I review the main points of this analysis. SUSY effects are parameterized using the mass insertion approximation formalism and differences with MSSM results are pointed out. Constraints on SUSY contributions coming from other processes ( e.g. b → sγ) are taken into account. Chargino and gluino contributions to photon and Z-mediated decays are computed and non-perturbative corrections are considered. We find that the integrated branching ratios and the asymmetries can be strongly modified. Moreover, the behavior of the differential Forward-Backward asymmetry remarkably changes with respect to the Standard Model expectation.

Formula omitted]decays in supersymmetry

We study the semileptonic decays B→ X s e + e −, B→ X s μ + μ − in generic supersymmetric extensions of the Standard Model. SUSY effects are parameterized using the mass insertion approximation formalism and differences with the Constrained MSSM results are pointed out. Constraints on SUSY contributions coming from other processes (e.g. b→ sγ) are taken into account. Chargino and gluino contributions to photon and Z-mediated decays are computed and non-perturbative corrections are considered. We find that the integrated branching ratios and the asymmetries can be strongly modified. Moreover, the behavior of the differential forward–backward asymmetry remarkably changes with respect to the Standard Model expectation.

B→sγwith large tan β in a MSSM analysis constrained by a realistic SO(10) model

Study of the MSSM in large tan$\beta$ regime has to include correlations between the constraints presented by the low energy values of the b quark mass and BR($b \to s\gamma$). Both quantities receive SUSY contributions enhanced by tan$\beta$ and have a major impact on the MSSM analysis. Here we summarize the results of such a study constrained by a complete SO(10) model. The dominant effects to the analysis come from third generation Yukawa couplings and a GUT threshold to $\alpha_s$. We show that a small negative GUT correction to $\alpha_s$ accommodates $\alpha_s(M_Z) \leq 0.118$ and $\delta m_b^{SUSY} > 0$. The latter quantity being positive then opens up two options to fit the measured rate for $b \to s\gamma$. The two distinct fits differ by the overall sign of the amplitude for this process. They work equally well in complementary regions of the allowed SUSY parameter space. We show plots of the partial contributions to the coefficient $C_7(M_Z)$ in the ($m_0,M_{1/2}$) plane in each of these best fits. We conclude that an attractive SO(10)-derived regime of the MSSM remains a viable option.

NLO corrections to ΔF = 2 effective hamiltonians and SUSY contribution to FCNC

The most general QCD-NLO Anomalous-Dimension Matrix of all four-fermion dimension six ΔF = 2 operators is presented. Two applications of this Anomalous-Dimension Matrix to the study of SUSY contribution to K − K − mixing are also discussed.

The $\gamma \gamma \to \gamma \gamma $ process in the standard and SUSY models at high energies

We study the helicity amplitudes of the process $\gamma \gamma \to \gamma \gamma$ at high energy, which in the standard and SUSY models first arise at the one-loop order. In the standard model (SM), the diagrams involve $W$ , charged-quark, and lepton loops, while in SUSY, we also have contributions from chargino-, charged-sfermion, and Higgs-loop diagrams. The SUSY contributions are most important in the region above the threshold for producing the supersymmetric partners; there, they interfere most effectively with the primarily imaginary SM amplitudes. Simple expressions for the relevant one-loop functions are given which provide a direct overview of the behaviour of the helicity amplitudes in the whole parameter space at high energies. The various characteristics of a large set of observables are studied in detail.

Weak magnetic dipole moments in the MSSM

We calculate the weak magnetic dipole moment of different fermions in the MSSM. In particular, we consider in detail the predictions for the WMDM of the τ lepton and bottom quark. We compare the purely SUSY contributions with two Higgs doublet models and SM predictions. For the τ lepton, we show that chargino diagrams give the main SUSY contribution, which for tan β = 50 can be one order of magnitude larger than the SM prediction. For the b quark, gluino diagrams provide the main SUSY contribution to its weak anomalous dipole moment, which is still dominated by gluon contributions. We also study how the universality assumption in the slepton sector induces correlations between the SUSY contributions to the τ WMDM and to ( g − 2) of the muon.

R-parity-conserving supersymmetry, neutrino mass, and neutrinoless double beta decay

We consider contributions of R-parity conserving softly broken supersymmetry (SUSY) to neutrinoless double beta ($\znbb$) decay via the (B-L)-violating sneutrino mass term. The latter is a generic ingredient of any weak-scale SUSY model with a Majorana neutrino mass. The new R-parity conserving SUSY contributions to $\znbb$ are realized at the level of box diagrams. We derive the effective Lagrangian describing the SUSY-box mechanism of $\znbb$-decay and the corresponding nuclear matrix elements. The 1-loop sneutrino contribution to the Majorana neutrino mass is also derived. Given the data on the $\znbb$-decay half-life of $^{76}$Ge and the neutrino mass we obtain constraints on the (B-L)-violating sneutrino mass. These constraints leave room for accelerator searches for certain manifestations of the 2nd and 3rd generation (B-L)-violating sneutrino mass term, but are most probably too tight for first generation (B-L)-violating sneutrino masses to be searched for directly.

CPViolatingBDecays in the Standard Model and Supersymmetry

We study the uncertainties of the standard model (SM) predictions for CP violating B decays and investigate where and how supersymmetric (SUSY) contributions may be disentangled. The first task is accomplished by letting the relevant matrix elements of the effective Hamiltonian vary within certain ranges. The SUSY analysis makes use of a formalism which allows one to obtain model-independent results. We show that in some cases it is possible (a) to measure the CP B‐BB mixing phase and (b) to discriminate the SM and SUSY contributions to the CP decay phases. The gold-plated decays in this respect are the B ! fKS and B ! KSp 0 channels. [S0031-9007(97)03711-3] PACS numbers: 11.30.Er, 12.15.Hh, 12.60.Jv, 13.25.Hw

The tan β − MH± bound from inclusive semi-tauonic B-decays in the MSSM

Abstract We compute the O(αs) SUSY-QCD corrections to the W and charged Higgs mediated inclusive semi-tauonic B-decay, B → τ ν T X . Combining the SUSY contribution with the SM result obtained from the heavy quark effective field theory, plus ordinary QCD corrections, we find that the allowed region in the (tan β, MH±)-plane could be significantly modified by the short-distance supersymmetric effects. Since the sensitivity to the SUSY parameters other than μ (the higgsino mixing mass) is rather low, the following effective bound emerges for μ 0 there could be no bound at all. Finally, we provide a combined (tan β, MH±) exclusion plot using our B-meson results together with the recent data from top quark decays.

SUSY and the mass difference of B0d – B̄ 0d

We present an overview of the loop corrections to the mass difference $\Delta m_{B_d^0}/ m_{B_d^0}$ within the minimal supersymmetric standard model. We include the complete mixing matrices of the charginos and neutralinos as well as of the scalar partners of the left and right handed third generation quarks. We show that the SUSY contribution to the mass difference in the $B_d^0$ system is comparable to the Standard Model one and can be even larger for the charged Higgs contribution and for a certain supersymmetric parameter space.

FCNC and CP constraints in extensions of the MSSM

In this talk I present the constraints on gluino- and photino- mediated SUSY contributions to FCNC and CP violation which are obtained in the model-independent parametrization known as mass insertion method. The results can be readily applied in testing extensions of the MSSM. I mention the implications of this analysis in the context of SUSY-GUT's and effective supergravities with flavour non-universality.

Susy contributions to Rb and top decay

I report on a systematic analysis of the MSSM parameter space to obtain the best SUSY solution to the $R_b$ anomaly within the constraint of top quark decay. Phenomenological implications for top decay and direct stop production at the Tevatron collider are discussed.

SUSY contributions to Rb and top quark decay.

Stop contributions to radiative corrections to R_b and the top quark decay are analysed over the relevant MSSM parameter space. One sees a 30 % increase in the former along with a similar drop in the latter in going from the higgsino dominated to the mixed region. Consequently one can get a viable SUSY contribution to R_b within the constraint of the top quark data only in the mixed region, corresponding to a photino dominated LSP. We discuss the phenomenological implications of this model for top quark decay and direct stop production, which can be tested with the Tevatron data.

A complete analysis of FCNC and CP constraints in general SUSY extensions of the standard model

We analyze the full set of constraints on gluino- and photino-mediated SUSY contributions to FCNC and CP violating phenomena. We use the mass insertion method, hence providing a model-independent parameterization which can be readily applied in testing extensions of the MSSM. In addition to clarifying controversial points in the literature, we provide a more exhaustive analysis of the CP constraints, in particular concerning ε′/ ε. As physically meaningful applications of our analysis, we study the implications in SUSY-GUT's and effective supergravities with flavour nonuniversality. This allows us to detail the domain of applicability and the correct procedure of implementation of the FC mass insertion approach.

Fourth generation and SUSY effects on CP violation in rare transitions

Abstract We have studied the CP asymmetry in B → K φ, K ∗φ transitions in the framework of the standard model (SM), its generalization to the four-generation case and in its supersymmetric (SUSY) extension. It is shown that in the SM and its SUSY extension with three generations, the asymmetry is less than one percent, but gets larger in the four-generation case, and its SUSY extension. It is shown that the asymmetry in the four-generation case is very sensitive to the gluon momentum. Further, we have shown that SUSY contributions change the sign and magnitude of the asymmetry in contrast to the four-generation case, for the same range of parameters in the SUSY extended case, as in the SM.

Neutrino magnetic moment inN=1 minimal supergravity

The complete one-loop supersymmetric (SUSY) correction to the magnetic moment (NMM) of a Dirac neutrino is calculated with allowance for mixing between the scalar leptons and for mixing between theW-gaugino and Higgs fermions. The contribution from the charged Higgs loop is negligible for all practical purpose. We thoroughly study the dependence of NMM on the SUSY parameters. The SUSY contribution to the NMM can be a few times less than or comparable to the value of the standard model (with a right-handed neutrino singlet added). The SUSY correction to the NMM increases with decreasing β value (tan β=〈H2〉/〈H1〉), and is not very sensitive to the charged scalar lepton mass.

Looking for supersymmetry in rare B-meson decays

We investigate manifestations of SUSY in rare B-meson decays B d →K φ 0, K + π − which proceed mainly via penguin diagrams. It is shown that there exists a range of masses of SUSY particles where the SUSY contribution to the amplitudes of the processes exceeds the standard one. We obtain constraints on SUSY particle masses which may be competitive with the accelerator ones.