arXiv subjects

Satoshi Mishima

Publications and source records attributed to Satoshi Mishima.

At least 37 records · Page 2Linked to original sources

arXiv2017

Revisiting Kaon Physics in General $Z$ Scenario

New physics contributions to the $Z$ penguin are revisited in the light of the recently-reported discrepancy of the direct CP violation in $K\toππ$. Interference effects between the standard model and new physics contributions to $ΔS = 2$ observables are taken into account. Although the effects are overlooked in the literature, they make experimental bounds significantly severer. It is shown that the new physics contributions must be tuned to enhance $\mathcal{B}(K_L \to π^{0} ν\barν)$, if the discrepancy of the direct CP violation is explained with satisfying the experimental constraints. The branching ratio can be as large as $6 \times 10^{-10}$ when the contributions are tuned at the 10 % level.

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arXiv2017

Electroweak precision constraints at present and future colliders

We revisit the global fit to electroweak precision observables in the Standard Model and present model-independent bounds on several general new physics scenarios. We present a projection of the fit based on the expected experimental improvements at future $e^+ e^-$ colliders, and compare the constraining power of some of the different experiments that have been proposed. All results have been obtained with the HEPfit code.

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arXiv2016

$B\to K^*\ell^+\ell^-$ in the Standard Model: Elaborations and Interpretations

Disentangling New Physics effects from the Standard Model requires a good understanding of all pieces that stem from the latter, especially the uncertainties that might plague the theoretical estimations within the Standard Model. In the light of recent measurements made in the decay of $B\to K^*\ell^+\ell^-$, and accompanying possibilities of New Physics effects, we re-examine the hadronic uncertainties that come about in this exclusive $b \to s$ transition. We show that it is not trivial to distinguish New Physics effects from these hadronic uncertainties and we attempt to quantify the latter in its magnitude and kinematic shape from the recent LHCb measurements of the angular observables in this decay mode. We also update our fit with the more recent calculations of the form factors combined with the ones computed with Lattice QCD.

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arXiv2016

Chargino contributions in light of recent $ε'/ε$

Recently, the standard model prediction of $ε'/ε$ was improved, and a discrepancy from the experimental results was reported at the $2.9σ$ level. We study the chargino contributions to $Z$ penguin especially with the vacuum stability constraint. The vacuum decay rate is investigated, and it is shown that the discrepancy can be explained if superparticles are lighter than 4-6 TeV. Correlations with $\mathcal{B}(K_L\toπ^0ν\barν)$ and other experimental constraints are also discussed.

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arXiv2016

$B\to K^* \ell^+ \ell^-$ decays at large recoil in the Standard Model: a theoretical reappraisal

We critically reassess the theoretical uncertainties in the Standard Model calculation of the $B \to K^* \ell^+ \ell^-$ observables, focusing on the low $q^2$ region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for $q^2 \sim 4 m_c^2\simeq 6.8$ GeV$^2$. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the $q^2$ dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.

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arXiv2015

Global Bayesian Analysis of the Higgs-boson Couplings

We present preliminary results of a bayesian fit to the Wilson coefficients of the Standard Model gauge invariant dimension-6 operators involving one or more Higgs fields, using data on electroweak precision observables and Higgs boson signal strengths.

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arXiv2014

Update of the electroweak precision fit, interplay with Higgs-boson signal strengths and model-independent constraints on new physics

We present updated global fits of the Standard Model and beyond to electroweak precision data, taking into account recent progress in theoretical calculations and experimental measurements. From the fits, we derive model-independent constraints on new physics by introducing oblique and epsilon parameters, and modified $Zb\bar{b}$ and $HVV$ couplings. Furthermore, we also perform fits of the scale factors of the Higgs-boson couplings to observed signal strengths of the Higgs boson.

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arXiv2014

Glauber gluons in spectator amplitudes for $B \to πM$ decays

We extract the Glauber divergences from the spectator amplitudes for two-body hadronic decays $B \to M_1 M_2$ in the $k_T$ factorization theorem, where $M_2$ denotes the meson emitted at the weak vertex. Employing the eikonal approximation, the divergences are factorized into the corresponding Glauber phase factors associated with the $M_1$ and $M_2$ mesons. It is observed that the latter factor enhances the spectator contribution to the color-suppressed tree amplitude by modifying the interference pattern between the two involved leading-order diagrams. The first factor rotates the enhanced spectator contribution by a phase, and changes its interference with other tree diagrams. The above Glauber effects are compared with the mechanism in elastic rescattering among various $M_1 M_2$ final states, which has been widely investigated in the literature. We postulate that only the Glauber effect associated with a pion is significant, due to its special role as a $q \bar q$ bound state and as a pseudo Nambu-Goldstone boson simultaneously. Treating the Glauber phases as additional inputs in the perturbative QCD (PQCD) approach, we find a good fit to all the $B \to ππ$, $πρ$, $πω$, and $πK$ data, and resolve the long-standing $ππ$ and $πK$ puzzles. The nontrivial success of this modified PQCD formalism is elaborated.

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arXiv2013

Electroweak Precision Observables, New Physics and the Nature of a 126 GeV Higgs Boson

We perform the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson, compare the results with the theoretical predictions and discuss the impact of recent experimental and theoretical improvements. We introduce New Physics contributions in a model-independent way and fit for the S, T and U parameters, for the $ε_{1,2,3,b}$ ones, for modified $Zb\bar{b}$ couplings and for a modified Higgs coupling to vector bosons. We point out that composite Higgs models are very strongly constrained. Finally, we compute the bounds on dimension-six operators relevant for the electroweak fit.

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arXiv2012

The Standard Model confronts CP violation in $D^0 \to π^+π^-$ and $D^0 \to K^+K^-$

The recently measured direct CP asymmetries in the processes $D^0\to π^+π^-$ and $D^0\to K^+K^-$ show a significant deviation from the naive Standard Model expectation. Using a general parameterization of the decay amplitudes, we show that the measured branching ratios imply large SU(3) breaking and large violations of the naive $1/N_c$ counting. Furthermore, rescattering constrains the I=0 amplitudes in the $ππ$ and $KK$ channels. Combining all this information, we show that, with present errors, the observed asymmetries are marginally compatible with the Standard Model. Improving the experimental accuracy could lead to an indirect signal of new physics.

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arXiv2011

Tetraquark-based analysis and predictions of the cross sections and distributions for the processes e^+ e^- --> Upsilon(1S) (pi^+ pi^-, K^+ K^-, eta pi^0) near Upsilon(5S)

We calculate the cross sections and final state distributions for the processes e^+ e^- --> Upsilon(1S) (pi^+ pi^-, K^+ K^-, eta pi^0) near the Upsilon(5S) resonance based on the tetraquark hypothesis. This framework is used to analyse the data on the Upsilon(1S) pi^+ pi^- and Upsilon(1S) K^+ K^- final states [K.F. Chen et al. (Belle Collaboration), Phys. Rev. Lett. 100, 112001 (2008); I. Adachi et al. (Belle Collaboration), arXiv:0808.2445], yielding good fits. Dimeson invariant mass spectra in these processes are shown to be dominated by the corresponding light scalar and tensor states. The resulting correlations among the cross sections are worked out. We also predict sigma(e^+ e^- --> Upsilon(1S) K^+ K^-)/sigma(e^+ e^- --> Upsilon(1S) K^0 Kbar^0) = 1/4. These features provide crucial tests of the tetraquark framework and can be searched for in the currently available and forthcoming data from the B factories.

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arXiv2011

Possible resolution of the B -> pi pi, pi K puzzles

We show that there exist uncanceled soft divergences in the k_T factorization for nonfactorizable amplitudes of two-body nonleptonic B meson decays, similar to those identified in hadron hadroproduction. These divergences can be grouped into a soft factor using the eikonal approximation, which is then treated as an additional nonperturbative input in the perturbative QCD formalism. Viewing the special role of the pion as a q-qbar bound state and as a pseudo Nambu-Goldstone boson, we postulate that the soft effect associated with it is significant. This soft factor enhances the nonfactorizable color-suppressed tree amplitudes, such that the branching ratios B(pi^0 pi^0) and B(pi^0 rho^0) are increased under the constraint of the B(rho^0 rho^0) data, the difference between the direct CP asymmetries A_{CP}(pi^\mp K^\pm) and A_{CP}(pi^0 K^\pm) is enlarged, and the mixing-induced CP asymmetry S_{pi^0 K_S} is reduced. Namely, the known pi pi and pi K puzzles can be resolved simultaneously.

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arXiv2011

Theoretical status of the B --> pi K decays

We review the theoretical status of the B --> pi K decays, focusing on recent developments in the QCD factorization and perturbative QCD approaches as well as on the Standard-Model correlation between the mixing-induced and direct CP asymmetries of the B^0 --> pi^0 K^0 mode.

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arXiv2009

Pion transition form factor in k_T factorization

It has been pointed out that the recent BaBar data on the pi gamma^* -> gamma transition form factor F_{pi gamma}(Q^2) at low (high) momentum transfer squared Q^2 indicate an asymptotic (flat) pion distribution amplitude. These seemingly contradictory observations can be reconciled in the k_T factorization theorem: the increase of the measured Q^2F_{pi gamma}(Q^2) for Q^2 > 10 GeV^2 is explained by convoluting a k_T dependent hard kernel with a flat pion distribution amplitude, k_T being a parton transverse momentum. The low Q^2 data are accommodated by including the resummation of alpha_s ln^2x, x being a parton momentum fraction, which provides a stronger suppression at the endpoints of x. The next-to-leading-order correction to the pion transition form factor is found to be less than 20% in the considered range of Q^2.

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arXiv2009

Comment on "Gauge Invariance and $k_T$-Factorization of Exclusive Processes"

We point out mistakes made in the one-loop calculation of some diagrams for the process $πγ^* \to γ$ in the preprint arXiv:0807.0296, and present correct results. Especially, we have difficulty to understand their argument that a highly off-shell gluon generates a light-cone (infrared) singularity. It is shown by means of the Ward identity that the gauge-dependent light-cone singularity found in arXiv:0807.0296 does not exist. It is then shown that a hard kernel derived in the $k_T$ factorization of exclusive processes is gauge invariant and free of the light-cone singularity.

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arXiv2007

Possible complex annihilation and B -> K pi direct CP asymmetry

We point out that a sizable strong phase could be generated from the penguin annihilation in the soft-collinear effective theory for B meson decays. Keeping a small scale suppressed by O(Lambda/m_b), Lambda being a hadronic scale and m_b the b quark mass, in the denominators of internal particle propagators without expansion, the resultant strong phase can accommodate the data of the B^0 -> K^-+ pi^+- direct CP asymmetry. Our study reconciles the opposite conclusions on the real or complex penguin annihilation amplitude drawn in the soft-collinear effective theory and in the perturbative QCD approach based on k_T factorization theorem.

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arXiv2007

Non-CKM induced flavor violation in "minimal" SUSY SU(5) models

Patterns of flavor violation induced by neutrino Yukawa couplings are discussed in realistic ``minimal'' SUSY SU(5) models, obtained by adding nonrenormalizable operators to the minimal one, in order to fix the fermion spectrum and suppress proton decay. Results are presented for the three possible implementations of the seesaw mechanisms, i.e. of Type I, II and III.

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arXiv2007

Fourth Generation CP Violation Effect on B -> K pi, phi K and rho K in NLO PQCD

We study the effect from a sequential fourth generation quark on penguin-dominated two-body nonleptonic B meson decays in the next-to-leading order perturbative QCD formalism. With an enhancement of the color-suppressed tree amplitude and possibility of a new CP phase in the electroweak penguin, we can account better for A_{CP}(B^0 -> K^+ pi^-)-A_{CP}(B^+ -> K^+ pi^0). Taking |V_{t's}V_{t'b}| \sim 0.02 with phase just below 90^\circ, which are consistent with the b -> s l^+ l^- rate and the B_s mixing parameter Δm_{B_s}, we find a downward shift in the mixing-induced CP asymmetries of B^0 -> K_S pi^0 and phi K_S. The predicted behavior for B^0 -> rho^0 K_S is opposite.

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