arXiv subjects

Janusz Rosiek

Publications and source records attributed to Janusz Rosiek.

30 records · Page 2Linked to original sources

arXiv2011

Complete One-Loop MSSM Predictions for B --> lepton lepton' at the Tevatron and LHC

During the last few years the Tevatron has dramatically improved the bounds on rare B-meson decays into two leptons. In the case of B_s --> mu+ mu-, the current bound is only ten times greater than the Standard Model expectation. Sensitivity to this decay is one of the benchmark goals for LHCb performance and physics. The Higgs penguin dominates this rate in the region of large tan(beta) of the MSSM. This is not necessarily the case in the region of low tan(beta), since box and Z-penguin diagrams may contribute at a comparable rate. In this article, we compute the complete one-loop MSSM contribution to B --> l+l'- for l,l' = e, mu. We study the predictions for general values of tan(beta) with arbitrary flavour mixing parameters. We discuss the possibility of both enhancing and suppressing the branching ratios relative to their Standard Model expectations. In particular, we find that there are "cancellation regions" in parameter space where the branching ratio is suppressed well below the Standard Model expectation, making it effectively invisible to the LHC.

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arXiv2010

SUSY_FLAVOR: a computational tool for FCNC and CP-violating processes in the MSSM

We present SUSY_FLAVOR -- a Fortran 77 program that calculates important leptonic and semi-leptonic low-energy observables in the general R-parity conserving MSSM. For a set of input MSSM parameters, the code gives predictions for the K0-bar K0, D-bar D, B_d-bar B_d and B_s-bar B_s mixing parameters; B to X_s gamma, B_{s,d} to l+ l-, K0_L to pi nu-bar nu and K+ to pi+ nu-bar nu decay branching ratios; and the electric dipole moments of the leptons and the neutron. All these quantities are calculated at one-loop level (with some higher-order QCD corrections included) in the exact sfermion mass eigenbasis, without resorting to mass insertion approximations.

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arXiv2009

MSSM Predictions for $B^0 \to μ^+ μ^-$ at Tevatron and LHC

During the last few years the Tevatron has improved the bounds on rare $B$-meson decays into two leptons. Sensitivity to this decay is also one of the benchmark goals for LHCb performance. We compute the complete 1-loop MSSM contribution to $B^0_{s,d}\to μ^+\^-mu$ and study the predictions for arbitrary flavour mixing parameters. We discuss the possibility of both enhancing and suppressing the branching ratios relative to their SM expectations. We find that there are ``cancellation regions'' in parameter space where the branching ratio is suppressed well below the SM expectation, making it effectively invisible to the LHC.

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arXiv2007

Seesaw mechanism in the sneutrino sector and its consequences

The seesaw-extended MSSM provides a framework in which the observed light neutrino masses and mixing angles can be generated in the context of a natural theory for the TeV-scale. Sneutrino-mixing phenomena provide valuable tools for connecting the physics of neutrinos and supersymmetry. We examine the theoretical structure of the seesaw-extended MSSM, retaining the full complexity of three generations of neutrinos and sneutrinos. In this general framework, new flavor-changing and CP-violating sneutrino processes are allowed, and are parameterized in terms of two $3\times 3$ matrices that respectively preserve and violate lepton number. The elements of these matrices can be bounded by analyzing the rate for rare flavor-changing decays of charged leptons and the one-loop contribution to neutrino masses. In the former case, new contributions arise in the seesaw extended model which are not present in the ordinary MSSM. In the latter case, sneutrino--antisneutrino mixing generates the leading correction at one-loop to neutrino masses, and could provide the origin of the observed texture of the light neutrino mass matrix. Finally, we derive general formulae for sneutrino--antisneutrino oscillations and sneutrino flavor-oscillations. Unfortunately, neither oscillation phenomena is likely to be observable at future colliders.

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arXiv2006

Neutrino masses in the Lepton Number Violating MSSM

We consider the most general supersymmetric model with minimal particle content and an additional discrete Z_3 symmetry (instead of R-parity), which allows lepton number violating terms and results in non-zero Majorana neutrino masses. We investigate whether the currently measured values for lepton masses and mixing can be reproduced. We set up a framework in which Lagrangian parameters can be initialised without recourse to assumptions concerning trilinear or bilinear superpotential terms, CP-conservation or intergenerational mixing and analyse in detail the one loop corrections to the neutrino masses. We present scenarios in which the experimental data are reproduced and show the effect varying lepton number violating couplings has on the predicted atmospheric and solar mass^2 differences. We find that with bilinear lepton number violating couplings in the superpotential of the order 1 MeV the atmospheric mass scale can be reproduced. Certain trilinear superpotential couplings, usually, of the order of the electron Yukawa coupling can give rise to either atmospheric or solar mass scales and bilinear supersymmetry breaking terms of the order 0.1 GeV^2 can set the solar mass scale. Further details of our calculation, Lagrangian, Feynman rules and relevant generic loop diagrams, are presented in three Appendices.

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arXiv2004

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.

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arXiv2002

Complete set of Feynman rules for the MSSM -- ERRATUM

This erratum contains the full corrected version of the paper {\em Complete set of Feynman rules for the Minimal Supersymmetric Standard Model}, published in Phys. Rev. D41 (3464) 1990. The complete set of Feynman rules for the R-parity conserving MSSM is listed, including the most general form of flavour mixing. Propagators and vertices are computed in t'Hooft-Feynman gauge, convenient for perturbative calculations beyond the tree level.

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arXiv2001

$ΔM_s/ΔM_d$, $\sin 2β$ and the angle $γ$ in the Presence of New $ΔF=2$ Operators

We present formulae for the mass differences $ΔM_d$ and $ΔM_s$ in the \BBds systems and for the CP violation parameter $ε$ which are valid in minimal flavour violation models giving rise to new four-fermion $ΔF=2$ operators. Short distance contributions to $ΔM_s$, $ΔM_d$ and $ε$ are parameterized by three {\it real} functions $F^s_{tt}$, $F^d_{tt}$ and $F^ε_{tt}$, respectively ($F^s_{tt} = F^d_{tt} = F^ε_{tt}$ holds only if the Standard Model $(V-A) \otimes (V-A)$ operators dominate). We present simple strategies involving the ratio $ΔM_s/ΔM_d$, $\sin2β$ and $γ$ that allow to search for the effects of the new operators. We point out that their sizable contributions to the ratio $ΔM_s/ΔM_d$ would in principle allow $γ$ to be larger than $90^\circ$. Constraints on the functions $F^i_{tt}$ imposed by the present (and future) experimental data are also discussed. As an example we show that for large $\tan\barβ\equiv v_2/v_1$ and $H^+$ not too heavy, $F^s_{tt}$ in the MSSM with heavy sparticles can be substantially smaller than in the SM due the charged Higgs box contributions and in particular due to the growing like $\tan^4\barβ$ contribution of the double penguin diagrams involving neutral Higgs boson exchanges. As a result the bounds on the function $F^s_{tt}$ can be violated which allows to exclude large mixing of stops. In this scenario the range of $\sin2β$ following from $ε$ and $ΔM_d$ is identical to the SM ones ($0.5<\sin 2β<0.8$). On the other hand $γ$ following from $ΔM_s/ΔM_d$ is lower.

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arXiv2001

$ΔF=2$ processes in the MSSM in large $\tanβ$ limit

We discuss corrections to $ΔM_{B_d}$, $ΔM_{B_s}$ and to the CP violation parameter $ε$ in two examples of (generalized) minimal flavour violation models: 2HDM and MSSM in the large $\tanβ$ limit. We show that for $H^+$ not too heavy, $ΔM_{B_s}$ in the MSSM with heavy sparticles can be substantially smaller than in the SM due the charged Higgs box contributions and in particular due to the growing like $\tan^4β$ contribution of the double penguin diagrams involving neutral Higgs boson exchanges.

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arXiv2000

Chargino searches at LEP for complex MSSM parameters

We reanalyze the results of the chargino searches at LEP (on the basis of the DELPHI 189 GeV data sample), including the possibility of complex MSSM parameters. We point out the possible differences between the complex- and real-parameter analysis. We check that the regions excluded by ``standard'' analyses remain generally robust against the introduction of complex parameters, with the exception of light sneutrino and low $\tanβ$ scenario, where additional constraints like those given by the $Z^0$ width or electric dipole moment measurements are necessary.

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arXiv1997

Supersymmetry and FCNC effects

We consider Flavour Changing Neutral Current processes in the framework of the supersymmetric extension of the Standard Model. FCNC constraints on the structure of sfermion mass matrices are reviewed. Furthermore, we analyze supersymmetric contributions to FCNC transitions which remain in the limit of flavour-conserving sfermion mass matrices. Implications of the FCNC constraints on the structure of sfermion mass matrices for SUSY breaking and sfermion mass generation are discussed. We conclude that the supersymmetric flavour problem is intriguing but perhaps not as severe as it is commonly believed.

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arXiv1995

Effects of R Parity Breaking in the Higgs Sector

We discuss possible manifestations of R parity breaking in the Higgs sector. We illustrate this with three examples: high-energy mono-photon production at LEP, calculation of limits on associated production of invisibly decaying Higgs bosons and discussion of non-standard scalar decays in the MSSM with broken R parity.

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