arXiv subjects

S. Khalil

Publications and source records attributed to S. Khalil.

At least 73 records · Page 4Linked to original sources

arXiv2005

Supersymmetric Models and CP violation in B decays

In this talk CP violation in the supersymmetric models, and especially in B-decays is discussed. We review our analysis of the supersymmetric contributions to the mixing CP asymmetries of $B\to ϕK_S$ and $B\to η^{\prime} K_S$ processes. Both gluino and chargino exchanges are considered in a model independent way by using the mass insertion approximation method. The QCD factorization method is used, and parametrization of this method in terms of Wilson coefficients is presented in both decay modes. Correlations between the CP asymmetries of these processes and the direct CP asymmetry in $b\to s γ$ decay are shown.

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arXiv2005

Comparative Study of CP Asymmetries in Supersymmetric Models

We systematically analyze the supersymmetric contributions to the mixing CP asymmetries and branching ratios of B -> Phi K(S) and B -> eta(prime) K(S) processes. We consider both gluino and chargino exchanges in a model independent way by using the mass insertion approximation method. While we adopt the QCD factorization approach for evaluating the corresponding hadronic matrix elements, a critical comparison with predictions in naive factorization one is also provided. We find that pure chargino contributions cannot accommodate the current experimental results on CP asymmetries, mainly due to b -> s gamma constraints. We show that charged Higgs contributions can relax these constraints making chargino responsible for large asymmetries. On the other hand, gluino exchanges can easily saturate both the constraints on B -> Phi K(S) and B -> eta(prime) K(S) CP asymmetries. Moreover, we also find that the simultaneous contributions from gluino and chargino exchanges could easily account for the present experimental results on the mentioned asymmetries. Remarkably, large experimentally allowed enhancements of B -> eta(prime) K(S) branching ratio can easily be achieved by the contribution of two mass insertions in gluino exchanges. Finally, we analyze the correlations between the CP asymmetries of these processes and the direct CP asymmetry in b -> s gamma decay. When all experimental constraints are satisfied, supersymmetry favors large and positive values of b -> s gamma asymmetry.

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arXiv2004

EDM constraints and CP asymmetries of B processes in supersymmetric models

We demonstrate that electric dipole moments (EDMs) strongly constrain possible SUSY contributions to the CP asymmetries of B processes; LL and/or RR flavour mixings between second and third generations are severely restricted by the experimental limit on the mercury EDM, and so therefore are their possible contributions to the CP asymmetries of B --> ϕK and B --> η' K. We find that SUSY models with dominant LR and RL mixing through non-universal A-terms is the only way to accommodate the apparent deviation of CP asymmetries from those expected in the Standard Model without conflicting with the EDM bounds or with any other experimental results.

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arXiv2004

Supersymmetric contributions to B --> K πbranching ratio

We analyze the supersymmetric contributions to the B --> Kπprocess. We show that the simultaneous contributions from the penguin diagrams with chargino and gluino in the loop could lead to a possible solution to the B --> K πpuzzle. Our result indicates that including the stringent constraint from the b --> s γbranching ratio, the supersymmeteric models with light right-handed top-squark and large mixing between second and third generation of up and down squarks is the most preferred by the current experimental data.

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arXiv2004

Top flavour violating decays in general supersymmetric models

We analyse the top flavour violating decays in general supersymmetric model using the mass insertion approximation. In particular, we discuss the impact of a light right-handed top-squark and large mixing between the first or second and third generation of up-squarks on processes as t -> q gamma,g . We also take into account the relevant experimental constraints from B-physics and the requirements for a successfull electroweak baryogenesis on squark mixings. We show that for general large mixings in squarks mass matrix, the branching ratio of the t -> q gamma, g (q=u,c) can be as large as 10^{-6}.

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arXiv2004

Fermion Masses and Mixing in Intersecting Branes Scenarios

We study the structure of Yukawa couplings in intersecting D6-branes wrapping a factorizable 6-torus compact space T^6. Models with MSSM-like spectrum are analyzed and found to fail in predicting the quark mass spectrum because of the way in which the family structure for the left-handed, right-handed quarks and, eventually, the Higgses is `factorized' among the different tori. In order to circumvent this, we present a model with three supersymmetric Higgs doublets which satisfies the anomaly cancellation condition in a more natural way than the previous models, where quarks were not treated universally regarding their branes assignments, or some particular branes were singled out being invariant under orientifold projection. In our model, the family structures for the left, right quarks, left leptons and the Higgses arise from one of the tori and can naturally lead to universal strength Yukawa couplings which accommodate the quark mass hierarchy and the mixing angles.

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arXiv2004

Flavor violation and extra dimensions

We analyze new sources of flavor violation in models with extra dimensions. We focus on three major classes of five dimensional models: models with universal extra dimension, models with split fermions, and models with warped extra dimension.We study the implications of these new sources on the associate CP violating asymmetries to the rare B-decays. We show that among these models only the split fermions scenario may accommodate the recent experimental deviation between the CP asymmetry of B_d -> phi K_S and sin 2 beta.

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arXiv2003

B_s^0 - bar{B}_s^0 Mixing and the B_s -> J/psi phi Asymmetry in Supersymmetric Models

We analyse supersymmetric contributions to B_s mixing and their impact on mixing-induced CP asymmetries, using the mass insertion approximation. We discuss in particular the correlation of SUSY effects in the CP asymmetries of B_s -> J/psi phi and B_d -> phi K_S and find that the mass insertions dominant in B_s mixing and B_d -> phi K_S are (delta_{23}^d)_{LL, RR} and (delta_{23}^d)_{LR, RL}, respectively. We show that models with dominant (delta_{23}^d)_{LR, RL} can accomodate a negative value of S_{phi K_S}, in agreement with the BELLE measurement of that observable, but yield a B_s mixing phase too small to be observed. On the other hand, models with dominant (delta_{23}^d)_{LL, RR} predict sizeable SUSY contributions to both Delta M_s and the mixing phase, but do not allow the asymmetry in B_d -> phi K_S to become negative, except for small values of the average down squark mass, which, in turn, entail a value of Delta M_s too large to be observed at the Tevatron and the LHC. We conclude that the observation of B_s mixing at hadron machines, together with the confirmation of a negative value of S_{phi K_S}, disfavours models with a single dominant mass insertion.

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arXiv2003

A possible supersymmetric solution to the discrepancy between B -> ϕK_S and B -> η' K_S CP asymmetries

We present a possible supersymmetric solution to the discrepancy between the observed mixing CP asymmetries in B -> ϕK_S and B -> η' K_S. We show that due to the different parity in the final states of these processes, their supersymmetric contributions from the R-sector have an opposite sign, which naturally explain the large deviation between S_{ϕK_S} and S_{η' K_S}. We also consider the proposed mechanisms to solve the puzzle of the observed large branching ratio of B -> η' K and study their impact on S_{eta' K_S}.

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arXiv2003

Supersymmetric contributions to the CP asymmetry of the B -> phi K_S and B -> eta' K_S

We analyse the CP asymmetry of the B -> phi K_S and B -> eta' K_S processes in general supersymmetric models. We show that chromomagnetic type of operator may play an important role in accounting for the deviation of the mixing CP asymmetry between B -> phi K_S and B -> J/psi K_S processes observed by Belle and BABAR experiments. We also show that due to the different parity in the final states of these processes, their supersymmetric contributions from the R-sector have an opposite sign, which naturally explain the large deviation between their asymmetries.

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arXiv2003

Chargino contributions to the CP asymmetry in B -> Phi K(S) decay

We perform a model independent analysis of the chargino contributions to the CP asymmetry in B -> Phi K(S) process. We use the mass insertion approximation method generalized by including the possibility of a light right-stop. We find that the dominant effect is given by the contributions of the mass insertions deltaU_LL(32) and deltaU_RL(32) to the Wilson coefficient of the chromomagnetic operator. By considering both these contributions simultaneously, the CP asymmetry in B -> Phi K(S) process is significantly reduced and negative values, which are within the 1-sigma experimental range and satisfy the b -> s gamma constraints, can be obtained.

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arXiv2003

Neutrino CP phases and lepton electric dipole moments in supersymmetric theories

We analyse the dependence of the electron electric dipole moment (EDM) on neutrino CP violating phases in the context of supersymmetric models. We start by studying the supersymmetric contributions to the lepton EDM and lepton flavour violation processes tau -> mu gamma and mu -> e gamma, in the framework of the mass insertion approximation, showing that, due to the large neutrino mixing, mu -> e gamma leads to severe constraints on the relevant mass insertions. We derive model independent bounds on these mass insertions and show that once these bounds are satisfied, the present experimental limits on electron EDM do not constraint the neutrino phases.

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arXiv2003

Supersymmetry and a rationale for small CP violating phases

We analyse the CP problem in the context of a supersymmetric extension of the standard model with universal strength of Yukawa couplings. A salient feature of these models is that the CP phases are constrained to be very small by the hierarchy of the quark masses, and the pattern of CKM mixing angles. This leads to a small amount of CP violation from the usual KM mechanism and a significant contribution from supersymmetry is required. Due to the large generation mixing in some of the supersymmetric interactions, the electric dipole moments impose severe constraints on the parameter space, forcing the trilinear couplings to be factorizable in matrix form. We find that the LL mass insertions give the dominant gluino contribution to saturate epsilon_K. The chargino contributions to epsilon'/epsilon are significant and can accommodate the experimental results. In this framework, the standard model gives a negligible contribution to the CP asymmetry in B-meson decay, a_{J/ψK_s}. However, due to supersymmetric contributions to B_d-\bar{B}_d mixing, the recent large value of a_{J/ψK_s} can be accommodated.

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arXiv2003

On supersymmetric contributions to the CP asymmetry of the B -> phi K_S

We analyse the CP asymmetry of the B -> phi K_S process in general supersymmetric models. In the framework of the mass insertion approximation, we derive model independent limits for the mixing CP asymmetry. We show that chromomagnetic type of operator may play an important role in accounting for the deviation of the mixing CP asymmetry between B -> phi K_S and B -> J/psi K_S processes observed by Belle and BaBar experiments. A possible correlation between the direct and mixing CP asymmetry is also discussed. Finally, we apply our result in minimal supergravity model and supersymmetric models with non-universal soft terms.

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arXiv2002

CP violation versus flavour in supersymmetric theories

We show that the quark flavour structure and CP violating phenomena are strongly correlated in supersymmetric theories. For a generic pattern of supersymmetry breaking the two broad categories of Yukawa couplings, democratic and hierarchical textures, have entirely different phenomenological implications. With hierarchical Yukawas, the rephasing invariant phase, arg(V_us V_cb V_cb^* V_cs^*), in the CKM mixing matrix has to be of order unity, while the SUSY CP violating phases are severely constrained by electric dipole moments, giving rise to the so-called SUSY CP problem. With democratic Yukawas, all experimental CP results can be accommodated with small values for the CKM and SUSY CP violating phases (i.e., CP can be considered as an approximate symmetry at the high energy scale). We also show that within this scenario, an entirely real CKM matrix in supersymmetric models is still allowed by the present experimental results.

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arXiv2002

Constraining supersymmetric models from B_d - B-bar_d mixing and the B_d --> J/psi K_S asymmetry

We analyze the chargino contributions to B_d - B-bar_d mixing and CP asymmetry of the B_d --> J/psi K_S decay, in the framework of the mass insertion approximation. We derive model independent bounds on the relevant mass insertions. Moreover, we study these contributions in supersymmetric models with minimal flavor violation, Hermitian flavor structure, and small CP violating phases and universal strength Yukawa couplings. We show that in supersymmetric models with large flavor mixing, the observed values of sin(2 beta) may be entirely due to the chargino-up-squark loops.

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arXiv2002

CP violation in supersymmetry with universal strength of Yukawa couplings

We analyse the CP problem in the context of a supersymmetric extension of the standard model with universal strength of Yukawa couplings. In these models we find a small amount of CP violation from the usual CKM mechanism and therefore a significant contribution from supersymmetry is required. The electric dipole moments impose severe constraints on the parameter space, forcing the trilinear couplings to be factorizable in matrix form. We find that the LL mass insertions give the dominant gluino contribution to saturate epsilon_K, while chargino contributions to epsilon'/epsilon are compatible with the experimental results. Due to significant supersymmetric contributions to B_d-\bar{B}_d mixing, the recent large value of a_{J/ψK_S} can be accommodated.

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arXiv2002

Flavor-dependent CP violation and electroweak baryogenesis in supersymmetric theories

We analyze electroweak baryogenesis in supersymmetric theories with flavor-dependent CP-violating phases. We generalize the standard approach to include the flavor dependence of the CP-violating sources and obtain an analytical approximate expression for the baryon asymmetry of the universe induced by these sources. It is shown that in the framework where the $μ$-term is real and the chargino sources vanish, large flavor mixing might lead to a substantial baryon asymmetry through the squark contributions, once the condition to have a strong first-order phase transition induced by light right-handed up squarks is relaxed. We derive model independent bounds on the relevant up-squark left-right mass insertions. We show that in supersymmetric models with non-minimal flavor structure these bounds can be reached and the required baryon asymmetry can be generated, while satisfying the constraints coming from the electric dipole moments.

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