Chargino Exchange Research Articles

Observables of low-lying supersymmetric vectorlike leptonic generations via loop corrections

A correlated analysis of observables arising from loop induced effects from a vectorlike generation is given. The observables include flavor changing radiative decays $\mu\to e \gamma, \tau\to \mu \gamma, \tau\to e \gamma$, electric dipole moments of the charged leptons $e,\mu, \tau$, and corrections to magnetic dipole moments of $g_\mu-2$ and $g_e-2$. In this work we give a full analysis of the corrections to these observables by taking into account both the supersymmetry loops as well as the exchange of a vectorlike leptonic generation. Thus the fermion mass matrix involves a $5\times 5$ mixing matrix while the scalar sector involves a $10\times 10$ mixing matrix including the CP violating phases from the vectorlike sector. The analysis is done under the constraint of the Higgs boson mass at the experimentally measured value. The loops considered include the exchange of $W$ and $Z$ bosons and of leptons and a mirror lepton, and the exchange of charginos and neutralinos, sleptons and mirror sleptons. The correction to the diphoton decay of the Higgs $h\to \gamma\gamma$ including the exchange of the vectorlike leptonic multiplet is also computed.

Quark-flavour violating Higgs decays to charm and bottom pairs in the MSSM

We calculate the decay width of h0→bb‾ in the Minimal Supersymmetric Standard Model (MSSM) with quark-flavour violation (QFV) at full one-loop level. The effect of c˜−t˜ mixing and s˜−b˜ mixing is studied taking into account the constraints from the B-meson data. We discuss and compare in detail the decays h0→cc‾ and h0→bb‾ within the framework of the perturbative mass insertion technique using the Flavour Expansion Theorem. The deviation of both decay widths from the Standard Model results can be quite large. While in h0→cc‾ it is almost entirely due to the flavour violating part of the MSSM, in h0→bb‾ it is mainly due to the flavour conserving part. Nevertheless, Γ(h0→bb‾) can fluctuate up to ∼7% due to QFV chargino exchange with large c˜−t˜ mixing.

Leptonicg−2moments,CPphases, and the Higgs boson mass constraint

Higgs boson mass measurement at $\sim 125$ GeV points to a high scale for SUSY specifically the scalar masses. If all the scalars are heavy, supersymmetric contribution to the leptonic $g-2$ moments will be significantly reduced. On the other hand the Brookhaven experiment indicates a 3sigma deviation from the standard model prediction. Here we analyze the leptonic $g-2$ moments in an extended MSSM model with inclusion of a vector like leptonic generation which brings in new sources of CP violation. In this work we consider the contributions to the leptonic $g-2$ moments arising from the exchange of charginos and neutralinos, sleptons and mirror sleptons, and from the exchange of $W$ and $Z$ bosons and of leptons and mirror leptons. We focus specifically on the $g-2$ moments for the muon and the electron where sensitive measurements exist. Here it is shown that one can get consistency with the current data on $g-2$ under the Higgs boson mass constraint. Dependence of the moments on CP phases from the extended sector are analyzed and it is shown that they are sensitively dependent on the phases from the new sector. It is shown that the corrections to the leptonic moments arising from the extended MSSM sector will be non-vanishing even if the SUSY scale extends into the PeV region.

The decays h 0 → b b ¯ $$ {h}^0\to b\overline{b} $$ and h 0 → c c ¯ $$ {h}^0\to c\overline{c} $$ in the light of the MSSM with quark flavour violation

We calculate the decay width of h0 -> b bbar in the Minimal Supersymmetric Standard Model (MSSM) with quark flavour violation (QFV) at full one-loop level. We study the effect of scharm-stop mixing and sstrange-sbottom mixing taking into account the constraints from the B meson data. We discuss and compare in detail the decays h0 -> c cbar and h0 -> b bbar within the framework of the perturbative mass insertion technique using the Flavour Expansion Theorem. The deviation of both decay widths from the Standard Model values can be quite large. Whereas in h0 -> c cbar it is almost entirely due to the flavour violating part of the MSSM, in h0 -> b bbar it is mainly due to the flavour conserving part. Nevertheless, the QFV contribution to Gamma(h0 -> b bbar) due to scharm-stop mixing and chargino exchange can go up to about 8%.

Chromoelectric dipole moments of quarks in MSSM extensions

An analysis is given of the chromoelectric dipole moment of quarks and of the neutron in an MSSM extension where the matter sector contains an extra vectorlike generation of quarks and mirror quarks. The analysis includes contributions to the CEDM from the exchange of the $W$ and the $Z$ bosons, from the exchange of charginos and neutralinos and the gluino. Their contribution to the EDM of quarks is investigated. The interference between the MSSM sector and the new sector with vectorlike quarks is investigated. It is shown that inclusion of the vectorlike quarks can modify the quark EDMs in a significant way. Further, this interference also provides a probe of the vectorlike quark sector. These results are of interest as in the future measurements on the neutron EDM could see an improvement up to two orders of magnitude over the current experimental limits and provide a window to new physics beyond the standard model.

μ→eγdecay in an MSSM extension

An analysis is given of the decay $\ensuremath{\mu}\ensuremath{\rightarrow}e+\ensuremath{\gamma}$ in an minimal supersymmetric standard model extension with a vectorlike generation. Here mixing with the mirrors allows the possibility of this decay. The analysis is done at the one-loop level with the exchange of charginos and neutralinos and of sleptons and mirror sleptons in the loops. A one-loop analysis with W- and Z-boson exchange and mirror leptons and neutrinos is also considered. The effects of $CP$-violating phases from the new sector on the decay $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ are analyzed in detail. The constraints arising from the current upper limit on the branching ratio $\mathcal{B}(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})$ from the MEG experiment of $2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ (at 90% C.L.) on the parameter space of supersymmetry (SUSY) models and on vectorlike models are explored. Further, the MEG experiment is likely to improve the upper limit by an order of magnitude in the coming years. The improved limits will allow one to probe a much larger domain of the parameter space of the extended models.

Electron electric dipole moment as a sensitive probe of PeV scale physics

We give a quantitative analysis of the electric dipole moments as a probe of high scale physics. We focus on the electric dipole moment of the electron since the limit on it is the most stringent. Further, theoretical computations of it are free of QCD uncertainties. The analysis presented here first explores the probe of high scales via electron EDM within MSSM where the contributions to the electric dipole moment (EDM) arise from the chargino and the neutralino exchanges in loops. Here it is shown that the electron EDM can probe mass scales from tens of TeV into the PeV range.The analysis is then extended to include a vectorlike generation which can mix with the three ordinary generations. Here new CP phases arise and it is shown that the electron EDM now has not only a supersymmetric contribution from the exchange of charginos and neutralinos but also a non-supersymmetric contribution from the exchange of W and Z bosons. It is further shown that the interference of the supersymmetric and the non-supersymmetric contribution leads to the remarkable phenomenon where the electron EDM as a function of the slepton mass first falls and become vanishingly small and then rises again as the slepton mass increases This phenomenon arises as a consequence of cancellation between the SUSY and the non-SUSY contribution at low scales while at high scales the SUSY contribution dies out and the EDM is controlled by the non-SUSY contribution alone. The high mass scales that can be probed by the EDM are far in excess of what accelerators will be able to probe. The sensitivity of the EDM to CP phases both in the SUSY and the non-SUSY sectors are also discussed.

Probe of new physics using precision measurement of the electron magnetic moment

The anomalous magnetic moment of the electron is determined experimentally with an accuracy of $2.8\times 10^{-13}$ and the uncertainty may decrease by an order of magnitude in the future. While the current data is in excellent agreement with the standard model, the possible future improvement in the error in $\Delta a_e= a_e^{\text{exp}}- a_e^{\text{theory}}$ has recently drawn interest in the electron anomalous magnetic moment as a possible probe of new physics beyond the standard model. In this work we give an analysis of such physics in an extension of the minimal supersymmetric standard model with a vector multiplet. In the extended model the electroweak contribution to the anomalous magnetic moment of the electron include loop diagrams involving in addition to the exchange of W and Z, the exchange of charginos, sneutrinos and mirror sneutrinos, and the exchange of neutralinos, sleptons and mirror sleptons. The analysis shows that a contribution to the electron magnetic moment much larger than expected by $m_e^2/m_\mu^2$ scaling of the deviation of the muon anomalous magnetic moment over the standard model prediction, i.e., $\Delta a_\mu = 3 \times 10^{-9}$ as given by the Brookhaven experiment, can be gotten within the MSSM extension. Effects of CP violating phases in the extended MSSM model on the corrections to the supersymmetric electroweak contributions to $a_e$ are also investigated. The analysis points to the possibility of detection of new physics effects with modest improvement on the error in $\Delta a_e= a_e^{\text{exp}} - a_e^{\text{theory}}$.

Large neutrino magnetic dipole moments in MSSM extensions

An analysis of the Dirac neutrino magnetic moment with standard model interactions gives ${\ensuremath{\mu}}_{\ensuremath{\nu}}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}19}{\ensuremath{\mu}}_{B}({m}_{\ensuremath{\nu}}/1\text{ }\text{ }\text{eV})$. The observation of a significantly larger magnetic moment will provide a clear signal of new physics beyond the standard model. The current experimental limits on the neutrino magnetic moments are orders of magnitude larger than the prediction with the standard model interactions and thus its test appears out of reach. Here we give an analysis of the Dirac neutrino magnetic moments within the framework of a minimal supersymmetric standard model extension with a vectorlike lepton generation. Specifically we compute the moments arising from the exchange of $W$ and the charged leptons in the loop, as well as from the exchange of charginos, charged sleptons and charged mirror sleptons. It is shown that the neutrino moment in this case can be several orders of magnitude larger than the one with standard model-like interactions, lying close to and below the current experimental upper limits and should be accessible in an improved future experiment. A correlated prediction of the heaviest neutrino lifetimes from radiative decays to the lighter neutrinos via exchange of charginos and sleptons in the loops is also made. The predicted lifetimes are several orders of magnitude smaller than the one with the standard model interactions and also lie close to the current experimental limits from analyses using the cosmic background neutrino data.

Radiative decays of cosmic background neutrinos in extensions of the MSSM with a vectorlike lepton generation

An analysis of radiative decays of the neutrinos ${\ensuremath{\nu}}_{j}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{l}\ensuremath{\gamma}$ is discussed in minimal supersymmetric standard model extensions with a vector like lepton generation. Specifically we compute neutrino decays arising from the exchange of charginos and charged sleptons where the photon is emitted by the charged particle in the loop. It is shown that while the lifetime of the neutrino decay in the Standard Model is $\ensuremath{\sim}{10}^{43}\text{ }\text{ }\mathrm{yrs}$ for a neutrino mass of 50 meV, the current lower limit from experiment from the analysis of the Cosmic Infrared Background is $\ensuremath{\sim}{10}^{12}\text{ }\text{ }\mathrm{yrs}$ and thus beyond the reach of experiment in the foreseeable future. However, in the extensions with a vectorlike lepton generation the lifetime for the decays can be as low as $\ensuremath{\sim}{10}^{12}--{10}^{14}\text{ }\text{ }\mathrm{yrs}$ and thus within reach of future improved experiments. The effect of $CP$ phases on the neutrino lifetime is also analyzed. It is shown that while both the magnetic and the electric transition dipole moments contribute to the neutrino lifetime, often the electric dipole moment dominates even for moderate size $CP$ phases.

τ→μγdecay in extensions with a vectorlike generation

An analysis is given of the decay $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}+\ensuremath{\gamma}$ in minimal supersymmetric standard model extensions with a vectorlike generation. Here mixing with the mirrors allows the possibility of this decay. The analysis is done at one loop with the exchange of charginos and neutralinos and of sleptons and mirror sleptons in the loops. It is shown that a branching ratio $\mathcal{B}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma})$ in the range $4.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\ensuremath{-}{10}^{\ensuremath{-}9}$ can be gotten which would be accessible to improved experiment such as at SuperB factories for this decay. The effects of $CP$ violation on this decay are also analyzed.

Supersymmetric contributions to ${\overline B_s} \to \phi {\pi^0}$ and ${\overline B_s} \to \phi {\rho^0}$ decays in SCET

We study the decay modes $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$ using Soft Collinear Effective Theory. Within Standard Model and including the error due to the SU(3) breaking effect in the SCET parameters we find that BR $\bar{B}_s\to \phi \pi^0 =7_{-1-2}^{+1+2}\times 10^{-8} $ and BR $\bar{B}_s\to \phi \pi^0=9_{-1-4}^{+1+3}\times 10^{-8}$ corresponding to solution 1 and solution 2 of the SCET parameters respectively.For the decay mode $\bar{B}_s\to \phi \rho^0$, we find that BR $\bar{B}_s\to \phi \rho^0 = 20.2^{+1+9}_{-1-12}\times 10^{-8} $ and BR $ \bar{B}_s\to \phi \rho^0 = 34.0^{+1.5 + 15}_{-1.5-22}\times 10^{-8} $ corresponding to solution 1 and solution 2 of the SCET parameters respectively. We extend our study to include supersymmetric models with non-universal A-terms where the dominant contributions arise from diagrams mediated by gluino and chargino exchanges. We show that gluino contributions can not lead to an enhancement of the branching ratios of $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$. In addition, we show that SUSY contributions mediated by chargino exchange can enhance the branching ratio of $\bar{B}_s\to \phi \pi^0$ by about 14% with respect to the SM prediction. For the branching ratio of $\bar{B}_s\to \phi \rho^0$, we find that SUSY contributions can enhance its value by about 1% with respect to the SM prediction.

CPasymmetries and branching ratios ofB→Kπin supersymmetric models

We analyze the supersymmetric contributions to the direct and mixing CP asymmetries and also to the branching ratios of the B --> K \pi decays in a model independent way. We consider both gluino and chargino exchanges and emphasize that a large gluino contribution is essential for saturating the direct and mixing CP asymmetries. We also find that combined contributions from the penguin diagrams with chargino and gluino in the loop could lead to a possible solution for the branching ratios puzzle and account for the results of R_c and R_n within b --> s \gamma constraints. When all relevant constraints are satisfied, our result indicates that supersymmetry favors lower values of R_c. Finally we study the correlations between the mixing CP asymmetry S_{K^0 \pi^0} and mixing CP asymmetries of the processes B --> \phi K and B --> \eta' K. We show that it is quite possible for gluino exchanges to accommodate the results of that observables

Comparative study of CP asymmetries in supersymmetric models

We systematically analyze the supersymmetric contributions to the mixing CP asymmetries and branching ratios of B → ϕ K S and B → η ′ 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 γ constraints. We show that charged Higgs contributions can relax these constraints making chargino responsible for large asymmetries. On the other hand, pure gluino exchanges can easily saturate both the constraints on B → ϕ K S and B → η ′ 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 → η ′ 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 γ decay. When all experimental constraints are satisfied, supersymmetry favors large and positive values of b → s γ asymmetry.

SUPERSYMMETRIC CONTRIBUTIONS TO THE CP ASYMMETRY OF THE B→ϕKS AND B→η'KS

We analyse the CP asymmetry of the B→ϕKS and B→η'KS processes in general supersymmetric models. We consider both gluino and chargino exchanges in a model-independent way by using the mass insertion approximation method. We adopt the QCD factorization method for evaluating the corresponding hadronic matrix elements. We show that chromomagnetic type of operator may play an important role in accounting for the deviation of the mixing CP asymmetry between B→ϕKS and B→J/ψKS 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.

Neutralino exchange corrections to the Higgs boson mixings with explicitCPviolation

A calculus for the derivatives of the eigenvalues of the neutralino mass matrix with respect to the $\mathrm{CP}$ violating background fields is developed and used to compute the mixings among the $\mathrm{CP}$ even and the $\mathrm{CP}$ odd Higgs sectors arising from the inclusion of the neutralino sector consisting of the neutralino, the Z boson, and the neutral Higgs bosons $({\ensuremath{\chi}}_{i}^{0}\ensuremath{-}Z\ensuremath{-}{h}^{0}\ensuremath{-}{H}^{0})$ exchange in the loop contribution to the effective potential including the effects of large $\mathrm{CP}$ violating phases. Along with the top squark, bottom squark, tau slepton and chargino--$W$--charged-Higgs-boson $({\ensuremath{\chi}}^{+}\ensuremath{-}W\ensuremath{-}{H}^{+})$ contributions computed previously the present analysis completes the one loop corrections to the Higgs boson mass matrix in the presence of large phases. $\mathrm{CP}$ violation in the neutral Higgs sector is discussed in the above framework with specific focus on the mixings of the $\mathrm{CP}$ even and the $\mathrm{CP}$ odd sectors arising from the neutralino sector. It is shown that numerically the effects of the neutralino exchange contribution on the mixings of the $\mathrm{CP}$ even and the $\mathrm{CP}$ odd sectors are comparable to the effects of the top squark and of the chargino exchange contributions and thus the neutralino exchange contribution must be included for a realistic analysis of mixings in the $\mathrm{CP}$ even and the $\mathrm{CP}$ odd sectors. Phenomenological implications of these results are discussed.

Erratum: Neutron and electron electric dipole moment inN=1supergravity unification [Phys. Rev. D57, 478 (1998)

An analysis of the neutron EDM and of the electron EDM in minimal N=1 supergravity unification with two CP violating phases is given. For the neutron the analysis includes the complete one loop gluino, chargino, and neutralino exchange diagrams for the electric dipole and the chromoelectric dipole operators, and also the contribution of the purely gluonic dimension six operator. It is shown that there exist significant regions in the six dimensional parameter space of the model where cancellations between the gluino and the chargino exchanges reduce the electric and the chromoelectric contributions, and further cancellations among the electric, the chromoelectric, and the purely gluonic parts lead to a dramatic lowering of the neutron EDM sometimes below the electron EDM value. This phenomenon gives a new mechanism, i.e., that of internal cancellations, for the suppression of the neutron EDM in supersymmetric theories. The cancellation mechanism can significantly reduce the severe fine tuning problem associated with CP violating phases in SUSY and SUGRA unified models.

Yukawa coupling corrections to stop, sbottom, and stau production in e+e− annihilation

We calculate within the MSSM the one-loop Yukawa coupling corrections to the processes e+ e- \to stops, sbottoms, and staus in order of Yukawa coupling squared. These corrections are due to the exchange of charginos, neutralinos, charged and neutral Higgs bosons, and charged and neutral Higgs ghosts. We give the complete analytical formulae. We also perform a detailed numerical analysis of the Yukawa coupling corrections, including also the SUSY-QCD corrections. It turns out that for stop and sbottom production the Yukawa coupling corrections are typically +/- 10% of the tree-level cross section. For stau production they are about +/- 5%.

Neutron and electron electric dipole moment inN=1supergravity unification

An analysis of the neutron EDM and of the electron EDM in minimal $N=1$ supergravity unification with two $\mathrm{CP}$-violating phases is given. For the neutron the analysis includes the complete one loop gluino, chargino, and neutralino exchange diagrams for the electric dipole and the chromoelectric dipole operators, and also the contribution of the purely gluonic dimension-six operator. It is shown that there exist significant regions in the six-dimensional parameter space of the model where cancellations between the gluino and the chargino exchanges reduce the electric and the chromoelectric contributions, and further cancellations among the electric, the chromoelectric, and the purely gluonic parts lead to a dramatic lowering of the neutron EDM sometimes below the electron EDM value. This phenomenon gives a new mechanism, i.e., that of internal cancellations, for the suppression of the neutron EDM in supersymmetric theories. The cancellation mechanism can significantly reduce the severe fine-tuning problem associated with $\mathrm{CP}$-violating phases in SUSY and SUGRA unified models.

Probing supergravity grand unification in the Brookhaven g-2 experiment.

A quantitative analysis of ${\mathit{a}}_{\mathrm{\ensuremath{\mu}}}$\ensuremath{\equiv}1/2(g-2${)}_{\mathrm{\ensuremath{\mu}}}$ within the framework of supergravity grand unification and radiative breaking of the electroweak symmetry is given. It is found that ${\mathit{a}}_{\mathrm{\ensuremath{\mu}}}^{\mathrm{SUSY}}$ is dominated by the chiral interference term from the light chargino exchange, and that this term carries a signature which correlates strongly with the sign of \ensuremath{\mu}. Thus as a rule ${\mathit{a}}_{\mathrm{\ensuremath{\mu}}}^{\mathrm{SUSY}}$>0 for \ensuremath{\mu}>0 and ${\mathit{a}}_{\mathrm{\ensuremath{\mu}}}^{\mathrm{SUSY}}$0 for \ensuremath{\mu}0 with very few exceptions when tan\ensuremath{\beta}\ensuremath{\sim}1. At the quantitative level it is shown that if the E821 BNL experiment can reach the expected sensitivity of 4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ and there is a reduction in the hadronic error by a factor of 4 or more, then the experiment will explore a majority of the parameter space in the ${\mathit{m}}_{0}$-${\mathit{m}}_{\mathit{g}\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}$ plane in the region ${\mathit{m}}_{0}$\ensuremath{\lesssim}400 GeV, ${\mathit{m}}_{\mathit{g}\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}$\ensuremath{\lesssim}700 GeV for tan\ensuremath{\beta}\ensuremath{\gtrsim}10 assuming the experiment will not discard the standard model result within its 2\ensuremath{\sigma} uncertainty limit. For smaller tan\ensuremath{\beta}, the SUSY reach of E821 will still be considerable. Further, if no effect within the 2\ensuremath{\sigma} limit of the standard model value is seen, then large tan\ensuremath{\beta} scenarios will be severely constrained within the current naturalness criterion, i.e., ${\mathit{m}}_{0}$,${\mathit{m}}_{\mathit{g}\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}$\ensuremath{\lesssim}1 TeV. \textcopyright{} 1996 The American Physical Society.