arXiv subjects

Seungwon Baek

Publications and source records attributed to Seungwon Baek.

At least 91 records · Page 5Linked to original sources

arXiv2005

Neutralino dark matter scattering and $B_s \to μ^+ μ^-$ in SUSY models

It is pointed out that there is a strong correlation between the neutralino dark matter scattering cross section $σ_{\tildeχ p}$ and the branching ratio for $B_s \to μ^+ μ^-$ within minimal supergravity (mSUGRA) and its extensions. This correlation arises mainly from $\tanβ$ and heavy neutral Higgs mass dependence, and shows a nice interplay between vastly different two observables within supersymmetric models. Current upper limit on $B(B_s \to μ^+ μ^-) < 5.8 \times 10^{-7}$ excludes substantial parameter space where $σ_{\tildeχ p}$ is within the CDMS sensitivity region.

hep-ph↗

arXiv2004

The B -> pi K Puzzle and New Physics

The present B -> pi K data is studied in the context of the standard model (SM) and with new physics (NP). We confirm that the SM has difficulties explaining the B -> pi K measurements. By adopting an effective-lagrangian parametrization of NP effects, we are able to rule out several classes of NP. Our model-independent analysis shows that the B -> pi K data can be accommodated by NP in the electroweak penguin sector.

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arXiv2004

A two-loop contribution to B_s --> mu^+ mu^- at large tan(beta) in the MSSM

We consider a two-loop contribution of Higgs-mediated penguin diagram to $B(B_s \to μ^+μ^-)$ at large $\tanβ$ in the MSSM, motivated by a recently proposed two-loop magnetic penguin diagrams by Chen and Geng [1]. Typically the two-loop diagram is a $α_s$ correction to the one-loop contributions. However the new contribution can dominate one-loop contributions in a region of parameter space where $μ$, $A_t$ and $A_b$ are very large and scalar top, scalar bottom and charged Higgs are light. Both constructive and destructive interferences are possible. The total branching ratio can be drastically changed from the one-loop result.

hep-ph↗

arXiv2003

CP violation in B --> phi K_S decay at large tan(beta)

We consider the chargino contribution to the CP violation in B \to ϕK_S decay in the minimal supersymmetric standard model at large \tanβ. It is shown that the Wilson coefficient C_{8g} of the chromomagnetic penguin operator can be significantly enhanced by the chargino-mediated diagrams while satisfying other direct/indirect experimental constraints. The enhanced C_{8g} allows large deviation in the CP asymmetry from the standard model prediction.

hep-ph↗

arXiv2003

SUSY breaking mediation mechanisms and (g-2)_μ, B -> X_s γ, B -> X_{s} l^+ l^- and B_s -> μ^+ μ^-

We show that there are qualitative differences in correlations among $(g-2)_μ$, $B\to X_s γ$, $B \to X_{s} l^+ l^-$ and $B_s \to μ^+ μ^-$ in various SUSY breaking mediation mechanisms: minimal supergravity (mSUGRA), gauge mediation (GMSB), anomaly mediation (AMSB), gaugino mediation ($\tilde{g}$MSB), weakly and strongly interacting string theories, and $D$ brane models. After imposing the direct search limits on the Higgs boson and SUSY particle search limits and $B\to X_s γ$ branching ratio, we find all the scenarios can accommodate the $a_μ\equiv (g-2)_μ/2 $ in the range of (a few tens)$\times 10^{-10}$, and predict that the branching ratio for $B\to X_s l^+ l^-$ can differ from the standard model (SM) prediction by $\pm 20 %$ but no more. On the other hand, the $B_s \to μ^+ μ^-$ is sensitive to the SUSY breaking mediation mechanisms through the pseudoscalar and stop masses ($m_A$ and $m_{\tilde{t}_1}$), and the stop mixing angle. In the GMSB with a small messenger number, the AMSB, the $\tilde{g}$MSB and the noscale scenarios, one finds that $B(B_s \to μ^+ μ^-) \lesssim 2 \times 10^{-8}$, which is below the search limit at the Tevatron Run II. Only the mSUGRA or string inspired models can generate a large branching ratio for this decay.

hep-ph↗

arXiv2003

Implications on SUSY breaking mediation mechanisms from observing $B_s \to μ^+ μ^-$ and the muon $(g-2)$

We consider $B_s \to μ^+ μ^-$ and the muon $(g-2)_μ$ in various SUSY breaking mediation mechanisms. If the decay $B_s \to μ^+ μ^-$ is observed at Tevatron Run II with a branching ratio larger than $\sim 2 \times 10^{-8} $, the noscale supergravity (including the gaugino mediation), the gauge mediation scenario with small number of messenger fields and low messenger scale, and a class of anomaly mediation scenarios will be excluded, even if they can accommodate a large muon $(g-2)_μ$. On the other hand, the minimal supergravity scenario and similar mechanisms derived from string models can accommodate this observation.

hep-ph↗

arXiv2003

CP violation in $B \to ϕK_S$ decay at large $\tanβ$

We consider the chargino contribution to the CP violation in $B \to ϕK_S$ decay in the minimal supersymmetric standard model at large $\tan\be$. It is shown that the Wilson coefficient $C_{8g}$ of the chromomagnetic penguin operator can be significantly enhanced by the chargino-mediated diagrams while satisfying other direct/indirect experimental constraints. The enhanced $C_{8g}$ allows large deviation in the CP asymmetry from the standard model prediction, especially it can explain the apparent anomaly reported by BaBar and Belle.

hep-ph↗

arXiv2002

B-decays at Large $\tanβ$ as a Probe of SUSY Breaking

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arXiv2002

Kaluza-Klein gravitino production with a single photon at e^+ e^- colliders

In a supersymmetric large extra dimension scenario, the production of Kaluza-Klein gravitinos accompanied by a photino at e^+ e^- colliders is studied. We assume that a bulk supersymmetry is softly broken on our brane such that the low-energy theory resembles the MSSM. Low energy supersymmetry breaking is further assumed as in GMSB, leading to sub-eV mass shift in each KK mode of the gravitino from the corresponding graviton KK mode. Since the photino decays within a detector due to its sufficiently large inclusive decay rate into a photon and a gravitino, the process e^+ e^- -> photino + gravitino yields single photon events with missing energy. Even if the total cross section can be substantial at sqrt(s)=500 GeV, the KK graviton background of e^+ e^- -> photon + graviton is kinematically advantageous and thus much larger. It is shown that the observable, sigma(e^-_L)-sigma(e^-_R), can completely eliminate the KK graviton background but retain most of the KK gravitino signal, which provides a unique and robust method to probe the supersymmetric bulk.

hep-ph↗

arXiv2002

Very light sbottom and gluino scenario confronting electroweak precision tests

The minimal supersymmetric model with light sbottom ($\sim m_b$) and light gluino (12 $\sim$ 16 GeV) can explain the excess of bottom quark production cross section at hadron colliders and has drawn much attention. We calculate one-loop contribution to Z-pole observable $R_b$ in this scenario when large CP violating phases are allowed in the gluino mass and/or sbottom sector. We show that these large CP violating phases can suppress the new contribution $δR_b$ safely within the experimental bounds even for heavier sbottom too heavy ($\wt{b}_2 \gtrsim$ 200 GeV) to be produced at LEP2 in association with light sbottom $\wt{b}_1$.

hep-ph↗

arXiv2001

Lepton flavor violating process in a supersymmetric grand unified theory with right-handed neutrino

Motivated from the recent results of neutrino oscillation experiment, we investigated lepton flavor violating (LFV) processes in a SU(5) supersymmetric grand unified theory with right-handed neutrino. The current experimental upper bound for $μ\to eγ$ process gives already some constraint on the model. Correlation between $μ\to e γ$ and the SUSY contribution to the muon anomalous magnetic moment is also discussed. Future LFV experiments will give considerable impacts on this type of SUSY GUT models equipped with seesaw neutrino mass generation.

hep-ph↗

arXiv2001

Two-loop Barr-Zee type Contributions to $(g-2)_μ$ in the MSSM

We consider the contribution of a two-loop Barr-Zee type diagram to $(g-2)_μ$ in the minimal supersymmetric standard model (MSSM). At relatively large $\tanβ$, we show that the contribution of light third generation scalar fermions and neutral CP-even Higgs, $h^0(H^0)$, can easily explain the very recent BNL experimental data. In our analysis $(g-2)_μ$ prefers negative $A_{f}$ and positive $μ$. It is more sensitive to the chirality flipping $h^0(H^0)\wt{f}_R^*\wt{f}_L$ rather than chirality conserving couplings.

hep-ph↗

arXiv2001

Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino

Motivated by the large mixing angle solutions for the atmospheric and solar neutrino anomalies, flavor changing neutral current processes and lepton flavor violating processes as well as the muon anomalous magnetic moment are analyzed in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to explain realistic mass relations for quarks and leptons, we take into account effects of higher dimensional operators above the GUT scale. It is shown that the supersymmetric (SUSY) contributions to the CP violation parameter in $K^0-\bar{K}^0$ mixing, $ε_K$, the $μ\to e γ$ branching ratio, and the muon anomalous magnetic moment become large in a wide range of parameter space. We also investigate correlations among these quantities. Within the current experimental bound of $\text{B}(μ\to e γ)$, large SUSY contributions are possible either in the muon anomalous magnetic moment or in $ε_K$. In the former case, the favorable value of the recent muon anomalous magnetic moment measurement at the BNL E821 experiment can be accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa phase can be different from the prediction within the Standard Model (SM) and therefore the measurements of the CP asymmetry of $B\to J/ψK_S$ mode and $Δm_{B_s}$ could discriminate this case from the SM. We also show that the $τ\to μγ$ branching ratio can be close to the current experimental upperbound and the mixing induced CP asymmetry of the radiative B decay can be enhanced in the case where the neutrino parameters correspond to the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.

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arXiv2001

Signatures of Non-commutative QED at Photon Colliders

In this paper we study non-commutative (NC) QED signatures at photon colliders through pair production of charged leptons $(\ell^+ \ell^-)$ and charged scalars $(H^+ H^-)$. The NC corrections for the fermion pair production can be easily obtained since NC QED with fermions has been extensively studied in the literature. NC QED with scalars is less studied. To obtain the cross section for $H^+H^-$ productions, we first investigate the structure of NC QED with scalars, and then study the corrections due to the NC geometry to the ordinary QED cross sections. Finally by folding in the photon spectra for a $γγ$ collider with laser back-scattered photons from the $e^+ e^-$ machine, we obtain 95% CL lower bound on the NC scale using the above two processes. We find that, with $\sqrt{s} = 0.5, 1.0$, and $ 1.5$ TeV and integrated luminosity $L = 500(fb^{-1})$, the NC scale up to 0.7, 1.2, and 1.6 TeV can be probed, respectively, while, for monochromatic photon beams, these numbers become 1.1, 1.7, 2.6 TeV, respectively.

hep-ph↗

arXiv2000

Neutrino Yukawa couplings and FCNC processes in B decays in SUSY-GUT

Flavor changing neutral current and lepton flavor violating processes are studied in the SU(5) SUSY-GUT with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of $b \to s γ$ can be as large as 20%. We also show that the $B_s$-$\bar{B}_s$ mixing can be significantly different from the standard model prediction.

hep-ph↗

arXiv2000

Neutrino oscillation, SUSY GUT and B decay

Effects of supersymmetric particles on flavor changing neutral current and lepton flavor violating processes are studied in the supersymmetric SU(5) grand unified theory with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of radiative B decay can be as large as 30% when the $τ\to μγ$ branching ratio becomes close to the present experimental upper bound. We also show that the $B_s$--$\bar{B}_s$ mixing can be significantly different from the presently allowed range in the standard model.

hep-ph↗

arXiv1999

Constraints on the R-parity Violating Couplings from $B^\pm \to l^\pm ν$ Decays

We derive the upper bounds on certain products of R-parity- and lepton-flavor-violating couplings from $B^\pm \to l^\pm ν$ decays. These modes of B-meson decays can constrain the product combinations of the couplings with one or more heavy generation indices which are comparable with or stronger than the present bounds. And we investigate the possible effects of R-parity violating interactions on $B_c \to l ν$ decays. These decay modes can be largely affected by R-parity violation.

hep-ph↗

arXiv1999

Probing SUSY-induced CP violations at B factories

In the minimal supersymmetric standard model (MSSM), the μ-parameter and the trilinear coupling A_t may be generically complex and can affect various observables at B factories. Imposing the edm constraints, we find that there is no new large phase shift in the B^0 - \bar{B^0} mixing, CP violating dilepton asymmetry is smaller than 0.1 %, and the direct CP violation in B\to X_s γcan be as large as \sim \pm 16 %.

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