K^+ -> pi^+ nu nu-bar and K_L -> pi^0 nu nu-bar Decays in the General MSSM

We reanalyze the rare decays K^+ -> pi^+ nu nu-bar and K_L -> pi^0 nu nu-bar in a general MSSM with conserved R-parity. Working in the mass eigenstate basis and performing adaptive scanning of a large space of supersymmetric parameters, 16 parameters in the constrained scan and 63 in the extended scan, we find that large departures from the Standard Model expectations are possible while satisfying all existing constraints. Both branching ratios can be as large as a few times 10^{-10} with Br(K_L -> pi^0 nu nu-bar) often larger than Br(K^+ -> pi^+ nu nu-bar) and close to its model independent upper bound. We give examples of supersymmetric parameters for which large departures from the SM expectations can be found and emphasize that the present 90% C.L. experimental upper bound on Br(K^+ -> pi^+ nu nu-bar) gives a non trivial constraint on the MSSM parameter space. Unlike previous analyses, we find that chargino box diagrams can give, already for moderately light charged sleptons, a significant contribution. As a byproduct we find that the ranges for the angles beta and gamma in the unitarity triangle are relaxed due to the presence of new CP-violating phases in K^0 - K^0-bar and B^0_d - B^0_d-bar mixing to 12 degrees <= beta <= 27 degrees and 20 degrees <= gamma <= 110 degrees.Comment: 36 pages, 27 figures, latex, uses axodraw.st

B->X_s l^+l^- in the MSSM at NNLO

We present the results of the calculation of QCD corrections to the matching conditions for the Wilson coefficients of operators mediating the transition b->s l^+l^- in the context of the MSSM. Within a scenario with decoupled heavy gluino the calculated contributions together with those present already in the literature allow for the first time a complete NNLO analysis of B->X_s l^+l^-. We study the impact of the QCD corrections and the reduction of renormalization scale dependencies for the dilepton invariant mass distribution and the forward-backward asymmetry in the inclusive decay B->X_s l^+l^- restricting the analysis to the "low-s" region and small values of tan(beta). The NNLO calculation allows to decrease the theoretical uncertainties related to the renormalization scale dependence below the size of supersymmetric effects in B->X_s l^+l^- depending on their magnitude. While it will be difficult to distinguish the MSSM expectations for the branching ratio from the Standard Model ones, this can become possible in the dilepton invariant mass distribution depending on the MSSM parameters and \hat{s}. In this respect the position of the zero of the forward-backward asymmetry s_0 is even more promising.Comment: 35 pages, 10 figure

Upper Bounds on Rare K and B Decays from Minimal Flavour Violation

We study the branching ratios of rare K and B decays in models with minimal flavour violation, using the presently available information from the universal unitarity triangle analysis and from the measurements of Br(B -> X_s gamma), Br(B -> X_s l^+l^-) and Br(K^+ -> pi^+ nu nubar). We find the following upper bounds: Br(K^+ -> pi^+ nu nubar) pi^0 nu nubar)< 4.6 10^{-11}, Br(K_L -> mu mubar)_{SD} X_s nu nubar)< 5.2 10^{-5}, Br(B -> X_d nu nubar) mu mubar)< 7.4 10^{-9}, Br(B_d -> mu mubar)< 2.2 10^{-10} at 95 % probability. We analyze in detail various possible scenarios with positive or negative interference of Standard Model and New Physics contributions, and show how an improvement of experimental data corresponding to the projected 2010 B factory integrated luminosities will allow to disentangle and test these different possibilities. Finally, anticipating that subsequently the leading role in constraining this kind of new physics will be taken over by the rare decays K^+ -> pi^+ nu nubar, K_L -> pi^0 nu nubar and B_{s,d} -> mu mubar, that are dominated by the Z^0 -penguin function C, we also present plots for several branching ratios as functions of C . We point out an interesting triple correlation between K^+ -> pi^+ nu nubar, B -> X_s gamma and B -> X_s l^+l^- present in MFV models.Comment: 26 pages, 12 figure

Power suppressed effects in B-> X_s gamma at O(alpha_s)

We compute the O(alpha_s) corrections to the Wilson coefficients of the dimension five operators emerging from the Operator Product Expansion of inclusive radiative B decays. We discuss the impact of the resulting O(alpha_s Lambda_QCD^2/m_b^2) corrections on the extraction of m_b and mu_pi^2 from the moments of the photon spectrum.Comment: 14 pages,4 figures, v2: comments and one figure on endpoint behaviour added, version to appear on NP

Seltene K und B Zerfälle im MSSM

In this thesis the rare decays (K^+,K_L) -> (pi^+,pi^0)v\bar{v} in general MSSM will be analyzed. The outcome is that both branching ratios can be as large as a few times 10^-10 with Br(K_L -> pi^0v\bar{v}) often larger than Br(K^+ -> pi^+v\bar{v}) and close to its model independent upper bound. Furthermore, QCD corrections to the inclusive decay \bar{B} -> X_sl^+l^- within the MSSM with a heavy and decoupled gluino are calculated. The impact of these corrections and the reduction of renormalization scale dependencies for the branching ratio, the differential decay distribution dG/ds, and the forward-backward asymmetry A_FB will be discussed. It follows that it will be difficult to distinguish the SM and MSSM expectations for the branching ratio, however, this can become possible for dG/ds, and in particular for the position of the zero of A_FB.In dieser Arbeit werden die Zerfälle (K^+,K_L) -> (pi^+,pi^0)v\bar{v} im allgemeinen MSSM analysiert. Es zeigt sich, dass beide Verzweigungsverhältnisse von der Grössenordnung 10^-10 sein können, wobei Br(K_L -> pi^0v\bar{v}) oft grösser als Br(K^+ -> pi^+v\bar{v}) und nahe der modellunabhängigen Grenze ist. Desweiteren werden QCD Korrekturen zum inklusiven Zerfall \bar{B} -> X_sl^+l^- im MSSM mit einem schweren und entkoppelten Gluino berechnet. Die Auswirkungen dieser Korrekturen auf das Verzweigungsverhältnis, die differentiellen Zerfallsbreite dG/ds und die vorwärts-rückwärts Asymmetrie A_FB, und insbesondere die Reduktion der Renormierungsskalenabhängigkeit in diesen Observablen, werden diskutiert. Es ergibt sich, dass eine Unterscheidung der Vorhersage des Verzweigungsverhältnisses im SM und im MSSM sehr schwer ist. Für dG/ds, und insbesondere für die Nullstelle von A_FB, ist dies allerdings möglich

Fermionic corrections to the interference of the electro- and chromomagnetic dipole operators in B¯→Xsγ at O(αs2)

AbstractWe calculate the virtual and bremsstrahlung fermionic corrections due to the interference of the electro- and chromomagnetic dipole operators in the inclusive B¯→Xsγ decay at O(αs2) and present analytical results for both the total decay rate and the photon energy spectrum