Triple product correlations in top squark decays

We propose several T-odd asymmetries in the decay chains of the top squarks $\tilde t_m \to t \tilde \chi^0_k$ and $t\to bW^+\to bl\nu$ and $\tilde\chi^0_k \to l^\pm\tilde l_n^\mp \to l^\pm l^\mp\tilde\chi^0_1$, for $l =e,\mu,\tau$. We calculate the asymmetries within the Minimal Supersymmetric Standard Model with complex parameters $M_1$, $\mu$ and $A_t$. We give the analytic formulae for the decay distributions. We present numerical results for the asymmetries and estimate the event rates necessary to observe them. The largest T-odd asymmetry can be as large as 40%.Comment: 26 pages, 5 figures; misprints corrected; reference adde

CP asymmetries in the supersymmetric trilepton signal at the LHC

In the CP-violating Minimal Supersymmetric Standard Model, we study the production of a neutralino-chargino pair at the LHC. For their decays into three leptons, we analyze CP asymmetries which are sensitive to the CP phases of the neutralino and chargino sector. We present analytical formulas for the entire production and decay process, and identify the CP-violating contributions in the spin correlation terms. This allows us to define the optimal CP asymmetries. We present a detailed numerical analysis of the cross sections, branching ratios, and the CP observables. For light neutralinos, charginos, and squarks, the asymmetries can reach several 10%. We estimate the discovery potential for the LHC to observe CP violation in the trilepton channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added, typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal C, Volume 72, Issue 3, 201

Tau-Sleptons and Tau-Sneutrino in the MSSM with Complex Parameters

We present a phenomenological study of tau-sleptons stau_1,2 and tau-sneutrino in the Minimal Supersymmetric Standard Model with complex parameters A_tau, mu and M_1. We analyse production and decays of stau_1,2 and tau-sneutrino at a future e^+ e^- collider. We present numerical predictions for the important decay rates, paying particular attention to their dependence on the complex parameters. The branching ratios of the fermionic decays of stau_1 and tau-sneutrino show a significant phase dependence for tan(beta) < 10. For tan(beta) > 10 the branching ratios for the stau_2 decays into Higgs bosons depend very sensitively on the phases. We show how information on the phase phi(A_tau) and the other fundamental stau parameters can be obtained from measurements of the stau masses, polarized cross sections and bosonic and fermionic decay branching ratios, for small and large tan(beta) values. We estimate the expected errors for these parameters. Given favorable conditions, the error of A_tau is about 10% to 20%, while the errors of the remaining stau parameters are in the range of approximately 1% to 3%. We also show that the induced electric dipole moment of the tau-lepton is well below the current experimental limit.Comment: LaTex, 25 pages, 11 figures (included); v2: extended discussion on error determination, version to appear in Phys.Rev.

Supersymmetric Electroweak Corrections to Heavier Top Squark Decay into Lighter Top Squark and Neutral Higgs Boson

We calculate the Yukawa corrections of order ${\cal O}(\alpha_{ew}m_{t(b)}^2/m_W^2)$, ${\cal O}(\alpha_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal O}(\alpha_{ew}m_{t(b)}^4/m_W^4)$ to the widths of the decays $\tilde t_2\to \tilde t_1 + (h^0,H^0,A^0)$ in the Minimal Supersymmetric Standard Model, and perform a detailed numerical analysis. We also compare the results with the ones presented in an earlier literature, where the ${\cal O}(\alpha_{s})$ SUSY-QCD corrections to the same three decay processes have been calculated. Our numerical results show that for the decays $\tilde t_2\to \tilde t_1 + h^{0}$, $\tilde t_2\to \tilde t_1 + H^{0}$, the Yukawa corrections are significant in most of the parameter range, which can reach a few ten percent, and for the decay $\tilde t_2\to\tilde t_1 + A^{0}$, the Yukawa corrections are relatively smaller, which are only a few percent. The numerical calculations also show that using the running quark masses and the running trilinear coupling $A_t$, which include the QCD, SUSY-QCD, SUSY-Electroweak effects and resume all high order ($\tan\beta$)-enhanced effects, can vastly improve the convergence of the perturbation expansion. We also discuss the effects of the running of the higgsino mass parameter $\mu$ on the corrections, and find that they are significant, too, especially for large $\tan\beta$.Comment: 37 pages, 19 eps figure

Effects of Lepton Flavour Violation on Chargino Production at the Linear Collider

We study the effects of lepton flavour violation (LFV) on the production processes e+e- --> \chi+_i \chi-_j at a linear collider with longitudinal e+ and e- beam polarizations. In the case of LFV the sneutrino mass eigenstates have no definite flavour, therefore, in the t-channel more than one sneutrino mass eigenstate can contribute to the chargino production cross sections. Our framework is the Minimal Supersymmetric Standard Model (MSSM) including LFV terms. We show that in spite of the restrictions on the LFV parameters due to the current limits on rare lepton decays, the cross section \sigma(e+e- --> \chi+_1 \chi-_1) can change by a factor of 2 or more when varying the LFV mixing angles. We point out that even if the present bound on BR(tau- --> e- gamma) improves by a factor of thousand the influence of LFV on the chargino production cross section can be significant. These results could have an important impact on the strategies for determining the underlying model parameters at the linear collider.Comment: 11pp; final version for JHE

Top Squarks and Bottom Squarks in the MSSM with Complex Parameters

We present a phenomenological study of top squarks (~t_1,2) and bottom squarks (~b_1,2) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, \mu and M_1. In particular we focus on the CP phase dependence of the branching ratios of (~t_1,2) and (~b_1,2) decays. We give the formulae of the two-body decay widths and present numerical results. We find that the effect of the phases on the (~t_1,2) and (~b_1,2) decays can be quite significant in a large region of the MSSM parameter space. This could have important implications for (~t_1,2) and (~b_1,2) searches and the MSSM parameter determination in future collider experiments. We have also estimated the accuracy expected in the determination of the parameters of ~t_i and ~b_i by a global fit of the measured masses, decay branching ratios and production cross sections at e^+ e^- linear colliders with polarized beams. Analysing two scenarios, we find that the fundamental parameters apart from A_t and A_b can be determined with errors of 1% to 2%, assuming an integrated luminosity of 1 ab^-1 and a sufficiently large c.m.s. energy to produce also the heavier ~t_2 and ~b_2 states. The parameter A_t can be determined with an error of 2 - 3%, whereas the error on A_b is likely to be of the order of 50%.Comment: 31 pages, 8 figures, comments and references added, conclusions unchanged; version to appear in Phys. Rev.

More on higher order decays of the lighter top squark

We discuss the three-body decays stop_1 -> W^+ b neutralino_1, stop_1 -> H^+ b neutralino_1, stop_1 -> b slepton_i neutrino_l, and stop_1 -> b sneutrino_l l^+$($l =e,\mu,\tau$) of the lighter top squark within the minimal supersymmetric standard model. We give the complete analytical formulas for the decay widths and present a numerical study in view of an upgraded Tevatron, the CERN LHC, and a future lepton collider demonstrating the importance of these decay modes.Comment: 29 pages, 6 PS-figures, uses revte

The top quark electric dipole moment in an MSSM extension with vector like multiplets

The electric dipole moment (EDM) of the top quark is calculated in a model with a vector like multiplet which mixes with the third generation in an extension of the MSSM. Such mixings allow for new CP violating phases. Including these new CP phases, the EDM of the top in this class of models is computed. The top EDM arises from loops involving the exchange of the W, the Z as well as from the exchange involving the charginos, the neutralinos, the gluino, and the vector like multiplet and their superpartners. The analysis of the EDM of the top is more complicated than for the light quarks because the mass of the external fermion, in this case the top quark mass cannot be ignored relative to the masses inside the loops. A numerical analysis is presented and it is shown that the top EDM could be close to $10^{-19} ecm$ consistent with the current limits on the EDM of the electron, the neutron and on atomic EDMs. A top EDM of size $10^{-19}ecm$ could be accessible in collider experiments such as the ILC.Comment: 21 pages and 5 figues. Accepted for publication in Physical Review

Supersymmetric Electroweak Corrections to Sbottom Decay into Lighter Stop and Charged Higgs Boson

The Yukawa corrections of order ${\cal O}(\alpha_{ew}m_{t(b)}^2/m_W^2)$, ${\cal O}(\alpha_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal O}(\alpha_{ew}m_{t(b)}^4/m_W^4)$ to the width of sbottom decay into lighter stop plus charged Higgs boson are calculated in the Minimal Supersymmetric Standard Model. These corrections depend on the masses of charged Higgs boson and lighter stop, and the parameters $\tan\beta$ and $\mu$. For favorable parameter values, the corrections decrease or increase the decay widths significantly. Especially for high values of $\tan\beta$(=30) the corrections exceed at least 10% for both $\tilde b_1$ and $\tilde b_2$ decay. But for low values of $\tan\beta$(=4,10) the corrections are small and the magnitudes are less than 10%. The numerical calculations also show that using the running bottom quark mass which includes the QCD effects and resums all high order $\tan\beta$-enhanced effects can improve much the convergence of the perturbation expansion.Comment: LateX, 27 pages, 13 ps figures. 12 figures updated, a figure and some references adde