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T. Yoshikawa

Publications and source records attributed to T. Yoshikawa.

32 records · Page 2Linked to original sources

Systematic Investigation of Possibilities for New Physics Effects in b --> s Penguin Processes

Although recent experimental results in b-->s penguin process seem to be roughly consistent with the standard model predictions, there may be still large possibilities of new physics hiding in this processes. Therefore, here we investigate systematically the potential new physics effects that may appear in time-dependent CP asymmetries of B --> phi K^0, B--> eta^\prime K^0 and B--> K^0 π^0 decay modes, by classifying the cases for the values of the mixing-induced indirect CP asymmetries, S_{phi K^0}, S_{eta^\prime K^0}, S_{K^0 pi^0} which are compared to S_{J/psi K^0}. We also show that several B_s decay modes may help to resolve the ambiguities in such an analysis. Through combining analysis with the time-dependent CP asymmetries of B_s decay modes such as B_s --> phi eta^\prime, B_s--> eta^\prime pi^0 and B_s --> K^0 bar{K}^0, we can determine where the new CP phases precisely come from.

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Search for New Physics in B Decays

We review recent important progresses at the B factories and discuss the future prospects. We also comment on how we might proceed to search for new physics.

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B-> X_sl^+l^- and B->Kπdecays in vectorlike quark model

In the framework of SU(2) singlet down type vectorlike quark model, we present a comprehensive analysis for decays B-> X_s γ, B->X_sl^+l^- and B-> Kπ. As for B-> X_sγ, we include the QCD running from the mass of the down-type vector quark D to weak scale in the scenario with the D quark much heavier than weak scale, and find that the running effect is small. Using the recent measurements of B-> X_sl^+l^-, we extract rather stringent constraints on the size and CP violating phase of z_{sb}, i.e., the tree level FCNC coupling for b-> sZ. Within the bounds, we investigate various observables such as forward-backward asymmetry of b->s l^+ l^-, the decay rates of B ->X_sγ, and B\to Kπ. We find that (1) The forward-backward asymmetry may have large derivation from that of the SM and is very sensitive to z_{sb}, and thus can be useful in probing the new physics.(2) By taking experimental errors at 2σlevel, both experimental measurements for B->X_sl^+l^- and B->Kπdecays can be explained in this model.

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Longitudinal polarization asymmetry of leptons in the pure leptonic B decays

Longitudinal lepton polarization asymmetry in B_q -> l l (q = d, s$ and l = e, mu, tau) decays is investigated. The analysis is done in a general manner by using the effective operators approach. It is shown that the longitudinal lepton polarization asymmetry would provide a direct search for the scalar and pseudoscalar type interactions, which are induced in all variants of Higgs-doublet models.

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Sufficiently Small $\barθ$ in $SU(3)^3 \times S_3$ Unification Model

Since CP violation in weak decays is successfully described by the KM mechanism, the strong CP problem cannot easily be accommodated. This leads us to reconsider the issue. If the axion and massless up quark are abandoned, we must extend the standard model. Extension to $SU(3)^3 \times S_3$ unification leads to the following situation: {\it if} CP is a high-energy symmetry and the appropriate symmetry-breaking hierarchy of scales is in place, then the $\barθ$ parameter of the QCD sub-theory is guaranteed to be sufficiently small. We find $\barθ < 10^{-11}$ while the empirical limit from the neutron electric dipole moment requires only that $\barθ < 1.3 \times 10^{-10}$.

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Measurement of the Width Difference of B_d Mesons

We estimate ΔGamma_d/Γ_d, including 1/m_b contributions and part of the next-to-leading order QCD corrections, and find it to be around 0.3%. We show the methods to measure ΔGamma_d/Γ_d by using at least two different final states on the untagged B_d decay. The nonzero width difference can also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the B_d-\bar{B}_d mixing phase. With the high statistics and accurate time resolution of the upcoming LHC experiment, the measurement of ΔGamma_d seems to be possible. This measurement would be important for an accurate measurement of \sin2ϕ_1 at the LHC. We also derive an upper bound on the value of ΔGamma_d/Γ_d in the presence of new physics.

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Measurement of the Lifetime Difference of $B_d$ Mesons: Possible and Worthwhile?

We estimate the decay width difference $ΔGamma_d / Γ_d$ in the $B_d$ system including $1/m_b$ contributions and next-to-leading order QCD corrections, and find it to be around 0.3%. We explicitly show that the time measurements of an untagged $B_d$ decaying to a single final state isotropically can only be sensitive to quadratic terms in $ΔGamma_d / Γ_d$, and hence the use of at least two different final states is desired. We discuss such pairs of candidate decay channels for the final states and explore the feasibility of a $ΔGamma_d / Γ_d$ measurement through them. The measurement of this width difference is essential for an accurate measurement of $\sin(2β)$ at the LHC. The nonzero width difference may also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the $B_d$-$\bar{B}_d$ mixing phase. We also derive an upper bound on the value of $ΔGamma_d / Γ_d$ in the presence of new physics, and point out some differences in the phenomenology of width differences in the $B_s$ and $B_d$ systems.

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The Effects of Non-Local Interactions in Rare B Decays, B -> X_s l^+l^-

The effects of non-local interactions in rare B decays, $\Bsll$, are investigated. We show the correlation between the branching ratio and the forward-backward asymmetry via two coefficients of the non-local interactions. This will certainly help us find any deviations from the standard model through the non-local interactions.

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A Systematic Analysis of the Lepton Polarization Asymmetries in the Rare B Decay, B -> X_sτ^+τ^-

The most general model-independent analysis of the lepton polarization asymmetries in the rare B decay, $\Bstt$, is presented. We present the longitudinal, normal and transverse polarization asymmetries for the $τ^+ $ and $τ^-$, and combinations of them, as functions of the Wilson coefficients of twelve independent four-Fermi interactions, ten of them local and two nonlocal. These procedures will tell us which type of operators contributes to the process. And it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and a deviation from the Standard Model is found.

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Searching for New Physics in the b->d FCNC using B_s^0(t)->ϕK_s and B_d^0(t)->K^0\bar{K}^0

Time-dependent measurements of the decays B_s^0(t)-->ϕK_s and B_d^0(t) --> K^0 \bar{K}^0 can be used to compare the weak phases of B_d^0-\bar{B}_d^0 mixing and the t-quark contribution to the b->d penguin. Since these two phases are equal in the standard model, any discrepancy would be a sign of new physics, specifically in the b->d flavour-changing neutral current (FCNC). The method can be applied to other pairs of decays, such as B_s^0(t)--> J/ΨK_s and B_d^0(t)--> J/Ψπ^0.

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A Model Independent Analysis of the Rare B Decay B -> X_s l^+ l^-

The most general model-independent analysis of the rare $B$ decay, $\Bsll$, is presented. There are ten independent local four-Fermi interactions which may contribute to this process. The branching ratio, the forward-backward asymmetry, and the double differential rate are written as functions of the Wilson coefficients of the ten operators. We also study the correlation between the branching ratio and the forward-backward asymmetry by changing each coefficient. This procedure tells us which types of operator contribute to the process, and it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and the deviation from the Standard Model is found.

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Test of the chiral structure and FCNC in the quark sector by radiative B meson decays

We study the effects of a vector-like SU(2) quark doublet as a fourth generation. In this model we examine the chiral structure and the FCNC in the quark sector by using radiative B meson decays in the allowed region for parameters from $R_b = {Γ_{qq}}/{Γ_{had.}}$. We compute the ratio $R = {Br (b \to d γ)}/{Br (b \to s γ)}$ in the model which realizes a different chiral structure as well as FCNC. The constraints has been extracted from the experimental results of B meson decays, the $T_{new}$ parameter of oblique corrections and $R_b$. Under the natural assumption that the violation of the $V-A$ structure in the light-quark sector is small, we can determine the allowed region for most of the mixings parameters and the vector-like quark masses. We show that there will be significant deviations in $R$ from the SM prediction due to the FCNC's and the violation of the $V-A$ structure.

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Using B_s^0 Decays to Determine the CP Angles αand γ

Dighe, Gronau and Rosner have shown that, by assuming SU(3) flavor symmetry and first-order SU(3) breaking, it is possible to extract the CP angles αand γfrom measurements of the decay rates of B_d^0(t) --> π^+π^-, B_d^0 --> π^- K^+ and B^+ --> π^+ K^0, along with their charge-conjugate processes. We extend their analysis to include the SU(3)-related decays B_s^0 --> π^+ K^-, B_s^0(t) --> K^+ K^- and B_s^0 --> K^0 {\bar K^0}. There are several advantages to this extension: discrete ambiguities are removed, fewer assumptions are necessary, and the method works even if all strong phases vanish. In addition, we show that γcan be obtained cleanly, with no penguin contamination, by using the two decays B_s^0(t) --> K^+ K^- and B_s^0 --> K^0 {\bar K^0}.

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Effective Lagrangian for a Technicolor Model without Exact Custodial Symmetry

Effective Lagrangian including technimesons is constructed for a realistic one-family Technicolor model without exact custodial symmetry. Tree level contribution to oblique correction parameters $S$ and $U$ due to spin 1 technimesons are computed with the effective Lagrangian. An isospin breaking term which is associated with technilepton vector mesons gives a negative contribution to the electroweak radiative correction parameter $S$ due to mixing between $I=0$ and $I=1$ vector mesons. $U$ receives non-zero contribution due to exotic left-handed charged vector mesons and its sign can be both negative and positive.

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