Search

We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium $\eta_t$ bound state of a top and anti-top quark, that then decays di-leptonically ($gg\to\eta_t \to \bar\ell \ell b \bar{b} \nu \bar{\nu}$). We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by `reconstructing' both its top and anti-top quark constituents in the di-lepton channel., Comment: 6 pages, 2 figures and 2 tables; matches published version

To measure the helicity of a spin-1 meson from the triple vector product of the three-momenta of its decay products, one needs information about the strong phase of the decay amplitude. In this paper, taking ${a}_{1}(1260)$ meson as an example, we present a method to extract information about the strong phase from the triple vector product of the pion momenta in the $W\ensuremath{\rightarrow}\ensuremath{\nu}\ensuremath{\tau}(\ensuremath{\rightarrow}\ensuremath{\nu}{a}_{1}(\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}))$ process, where the ${a}_{1}$ helicity is known a priori from electroweak theory. This process is advantageous in that highly boosted ${a}_{1}^{\ensuremath{-}}$ mesons from ${\ensuremath{\tau}}_{L}^{\ensuremath{-}}$ decays have nearly maximal helicity asymmetry and thus most reflect the strong phase. We revisit the theoretical calculation of the ${a}_{1}$ meson helicity in the $W\ensuremath{\rightarrow}\ensuremath{\nu}\ensuremath{\tau}(\ensuremath{\rightarrow}\ensuremath{\nu}{a}_{1})$ process. Next, we formulate the differential decay rate of polarized ${a}_{1}$ mesons in a manner convenient for the study of the ${a}_{1}$ meson helicity asymmetry. Finally, we present the method for extracting information about the strong phase, and assess its feasibility at the LHC.

The conjoined production at the LHC of single top and Higgs boson via $t$-channel weak boson exchange is ideal to probe the top-quark Yukawa coupling, due to a delicate cancellation between the amplitudes with the $htt$ and the $hWW$ couplings. We find that the top quark is produced with $100\%$ polarization in the leading order, and its quantum state is determined by the spin-vector direction in the $t$-quark rest frame. We relate the spin direction to the four-momenta of the top, Higgs and a jet in the helicity amplitude framework. We identify a polarization asymmetry that is sensitive to CP violation, even after partial integration over the forward jet momentum. This CP violating asymmetry may be observed at the LHC via the component of the top-quark polarization that is perpendicular to the $th$ scattering plane., Comment: 5 pages, 5 figures; typos corrected, references added

A short review is given on the status of the anomalous magnetic moment of the muon, g − 2 . Emphasis is put on recent developments in the different sectors and the accuracy of the Standard Model prediction. We comment on the prospects for further improvements in time for the upcoming g − 2 experiments and on New Physics explanations of the discrepancy, which has been further consolidated.

We propose a novel method to reconstruct event by event the full kinematics of the cascade decay process, $h\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}({\ensuremath{\pi}}^{+}\overline{\ensuremath{\nu}})({\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\nu})$, which allows us to measure the ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ spin correlation, a measure of the $CP$ property of the Higgs boson. By noting that the ${\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}$ momenta lie on the plane spanned by the accurately measured impact parameter and momentum vectors of charged pions, we can obtain the most likely momenta of the two missing neutrinos by using the probability distribution functions of the ${\stackrel{\ensuremath{\rightarrow}}{\overline{)p}}}_{T}$ vector and the location of the primary vertex. A simple detector level simulation shows an excellent agreement between the reconstructed and the true kinematics, both in the ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ and the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ rest frames. The method can be tested in $Z\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ events, which should exhibit no correlation.

We revisit the sensitivity study of the Tokai-to-Kamioka-and-Korea (T2KK) and Tokai-to-Kamioka-and-Oki (T2KO) proposals where a water Cerenkov detector with the 100 kton fiducial volume is placed in Korea ($L = 1000$ km) and Oki island ($L = 653$ km) in Japan, respectively, in addition to the Super-Kamiokande for determination of the neutrino mass hierarchy and leptonic CP phase ($\delta_{CP}$). We systematically study the running ratio of the $\nu_\mu$ and $\bar{\nu}_\mu$ focusing beams with dedicated background estimation for the $\nu_e$ appearance and $\nu_\mu$ disappearance signals, especially improving treatment of the neutral current $\pi^0$ backgrounds. Using a $\nu_\mu$ - $\bar{\nu}_\mu$ beam ratio between 3 : 2 and 2.5 : 2.5 (in unit of $10^{21}$POT with the proton energy of 40 GeV), the mass hierarchy determination with the median sensitivity of 3 - 5 $\sigma$ by the T2KK and 1 - 4 $\sigma$ by the T2KO experiment are expected when $\sin^2\theta_{23} = 0.5$, depending on the mass hierarchy pattern and CP phase. These sensitivities are enhanced (reduced) by $30\%$ - $40\%$ in $\Delta \chi^2$ when $\sin^2\theta_{23} = 0.6\, (0.4)$. The CP phase is measured with the uncertainty of $20^\circ$ - $50^\circ$ by the T2KK and T2KO using the $\nu_\mu$ - $\bar{\nu}_\mu$ focusing beam ratio between 3.5 : 1.5 and 1.5 : 3.5. These findings indicate that inclusion of the $\bar{\nu}_\mu$ focusing beam improves the sensitivities of the T2KK and T2KO experiments to both the mass hierarchy determination and leptonic CP phase measurement simultaneously with the preferred beam ratio being between 3 : 2 - 2.5 : 2.5 ($\times 10^{21}$POT).

We revisit the current LHC constraints on the electroweak-ino sector parameters in the minimal supersymmetric standard model (MSSM) that are relevant to explaining the $(g-2)_\mu$ anomaly via the dominant chargino and muon sneutrino loop. Since the LHC bounds on electroweak-inos become weaker if they decay via an intermediate stau or a tau sneutrino instead of the first two generation sleptons, we perform a detailed analysis of the scenario with a bino as the lightest supersymmetric particle (LSP) and a light stau as the next-to-lightest one (NLSP). Even in this scenario, the chargino sector parameters in the MSSM that can account for the $(g-2)_\mu$ anomaly within $1 \sigma$ are already found to be significantly constrained by the 8 TeV LHC and the available subset of the 13 TeV LHC limits. We also estimate the current LHC exclusions in the left-smuon (and/or left-selectron) NLSP scenario from multilepton searches, and further combine the constraints from the multi-tau and multi-lepton channels for a mass spectrum in which all three generations of sleptons are lighter than the chargino. In the latter two cases, small corners of the $1 \sigma$ favoured region for $(g-2)_\mu$ are still allowed at present., Comment: 28 pages, 14 figures; v2: Note added with updated 13 TeV LHC constraints using 36.1 fb^{-1} results, version to appear in Physical Review D

We study the CP violation in the Higgs boson and toponia production process at the ILC where the toponia are produced near the threshold. With the approximation that the production vertex of the Higgs boson and toponia is contact, and neglecting the P-wave toponia, we analytically calculated the density matrix for the production and decay of the toponia. Under these assumptions, the production spectrum of the toponia is solely determined by the spin quantum number, therefore the toponia can be either singlet or triplet. We find that the production rate of the singlet toponium is highly suppressed, and behaves just like the production of a P-wave toponia. In the case of the triplet toponium, three completely independent CP observables, namely azimuthal angles of lepton and anti-lepton in the toponium rest-frame as well as their sum, are predicted based on our analytical results, and checked by using the tree-level event generator. The non-trivial correlations come from the longitudinal-transverse interferences for the azimuthal angles of leptons, and the transverse-transverse interference for their sum. These three observables are well defined at the ILC, where the rest frame of the toponium can be reconstructed directly. Furthermore, the QCD-strong corrections, which are important near the threshold region, are also studied with the approximation of spin-independent QCD-Coulomb potential. While the total cross section is enhanced, the spin correlations predicted in this paper are not affected., Comment: 32pages, 18figures, KEK-TH-1877. Accepted version by JHEP

We review the status of the Standard Model prediction of the anomalous magnetic moment of the muon and the electromagnetic coupling at the scale M Z . Recent progress in the evaluation of the hadronic contributions have consolidated the prediction of both quantities. For g − 2 , the discrepancy between the measurement from BNL and the Standard Model prediction stands at a level of more than three standard deviations.

We briefly review the Standard Model prediction of g − 2 of the muon and confront it with the formidably accurate measurement from BNL. The focus is on recent improvements of the hadronic vacuum polarisation contributions. We also calculate the running QED coupling at space- and time-like momentum transfer. Its value at the scale of the Z boson mass, α ( M Z 2 ) , is an important ingredient in electroweak precision fits and its prediction is improved considerably.

We update our Standard Model predictions for g-2 of the muon and for the hadronic contributions to the running of the QED coupling, Delta alpha^5_had(M_Z^2). Particular emphasis is put on recent changes in the hadronic contributions from new data in the 2pi channel and from the energy region just below 2 GeV.

Fortran subroutines to calculate helicity amplitudes with massive spin-2 particles (massive gravitons), which couple to the standard model particles via the energy momentum tensor, are added to the {\tt HELAS} ({\tt HEL}icity {\tt A}mplitude {\tt S}ubroutines) library. They are coded in such a way that arbitrary scattering amplitudes with one graviton production and its decays can be generated automatically by {\tt MadGraph} and {\tt MadEvent}, after slight modifications. All the codes have been tested carefully by making use of the invariance of the helicity amplitudes under the gauge and general coordinate transformations., 11 pages, 2 figures

We update the Standard Model predictions of the anomalous magnetic moment of the muon, a_\mu = (g-2)/2, and the value of the QED coupling at the Z-boson mass, incorporating the new e^+e^- \to \pi\pi data obtained by CMD-2 and KLOE, as well as the corrected SND data, and other improvements. The prediction for a_\mu=11659180.4 (5.1) \times 10^{-10} is about 3 \times 10^{-10} lower than before, and has a smaller uncertainty, which corresponds to a 3.4\sigma deviation from the measured value. The prediction for the QED coupling is \alpha(M_Z^2)^{-1}= 128.937 \pm 0.030.

We consider a light supersymmetric top-quark (top-squark) scenario, where a top squark and a neutralino are the lightest supersymmetric particles and the top-squark mass is close to the sum of the neutralino mass and the top-quark mass. In this scenario, the top quark and the neutralino coming from the decay of a top squark have almost equal velocity vectors, and hence the missing transverse momentum in top-squark pair production events at colliders is suppressed, which makes the top-squark search challenging, as in the degenerate scenario where the top-squark mass and the neutralino mass are similar. In this paper, we propose a novel analysis technique aimed at discovering the top-squark pair production signal in such an ``equal-velocity'' scenario. The key is to look for events where the missing transverse momentum vector is proportional to the transverse momentum vector of the top-quark pair with specific values for the proportionality coefficient, as this coefficient is equal to the ratio of the neutralino mass over the top-quark mass in the equal-velocity limit. We examine the possibility that the top-squark signal can be identified at the $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$ LHC using our analysis method.

Combining neutrino oscillations at T2K or T2HK with antineutrinos oscillations from muon decay at rest (DAR) allows a determination of the leptonic CP-violating phase delta. The degeneracies of this phase with theta13 and theta23 are broken and delta can be reliably distinguished from 180-delta. We present the sensitivity to delta of T2(H)K together with a muon DAR experiment using Super-K as a near detector and Hyper-K at the Tochibora site as a far detector., Comment: 24 pages, 8 figures, v2 Includes CCQE and nu-e elastic backgrounds

We studied τ polarization effects on the decay distributions of τ produced in the CNGS ν τ appearance experiments. We show that energy and angular distributions for the decay products in the laboratory frame are significantly affected by the τ polarization. Rather strong azimuthal asymmetry about the τ momentum axis is predicted, which may have observable consequences in experiments even with small statistics.

We studied the decay distributions of τ leptons produced in neutrino-nucleon scattering via charged current interaction, taking into account the τ polarization, for the long baseline neutrino oscillation experiments which aim to observe ν τ appearance. The information on the τ polarization is essential for measuring ν τ appearance since the decay particle distributions depend crucially on the τ spin. We show that τ produced via neutrino has high degree of polarization, and its spin direction depends non-trivially on the energy and the scattering angle of τ in the laboratory frame. We also show that the subsequent decay distributions are significantly affected by the produced τ polarization.

We studied polarization effects in tau production by neutrino-nucleon scattering. Quasi-elastic scattering, $Delta$ resonance production and deep inelastic scattering processes are taken into account for the CERN-to-Gran Sasso projects. We show that the tau produced by neutrino has high degree of polarization, and its spin direction depends non-trivially on the energy and the scattering angle of tau in the laboratory frame., 6 pages, 5 eps figures, espcrc2.sty; Proceedings of the 3rd International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region (NuInt04), March 17-21, 2004, Gran Sasso, Italy; minor changes, typos in Eq. (6) corrected

【背景・目的】 造血肝細胞移植を受けた患者が退院後に遭遇する困難と移植を受けたことで変化した生活を再構築できる要因を明らかにすることを目的とした. 【対象と方法】 G病院血液内科にて移植を受けた患者で順調に経過し, 重篤な移植片対症候群や免疫不全がない13名に半構成的面接を行った. 面接内容を逐語録に起こし, 質的帰納的方法を参考に, 患者の言動から造血幹細胞移植患者が退院後に遭遇する困難と移植後の生活を再構築できる要因に関する言動をコード化し類似性に従いサブカテゴリー, カテゴリーと抽象化を行った. 【結果】 退院後に遭遇する困難は『病気の不確実性』『変化した生活が辛く哀しい』『今までと違う体力』『身体的変化』『周囲への気兼ね』のカテゴリーが抽出された. 移植後の生活を再構築できる要因としては『前向きに生きる決意』『夫婦の価値観の変化』『自分のペースで生活』『経済生活の基盤の変化』『苦悩を支えられた体験』のカテゴリーが抽出された. 【結語】 移植看護において移植を受けた患者が退院後の生活を再構築するためには, 患者を支えるサポートが重要であることが示唆された.

We study the renormalization of the nonlinear realization of the SU ( 2 ) Higgs model in the modified minimal subtraction renormalization scheme. We propose that the effective field method with truncated operator series is trustworthy even when the Higgs boson is relatively light. Using the technique of background field method in the coordinate space, we derive the matching conditions at tree and one-loop order, both in the regions where the Higgs boson is heavy and where it is light. We obtain the complete one-loop anomalous couplings up to O ( p 4 ) in the SU ( 2 ) Higgs model. We observe that the contribution of the gauge bosons and the Goldstone bosons to the anomalous couplings at the one-loop level is significant. By establishing the correspondence between our coordinate space calculation and the momentum space calculation that exists in the literature, we find agreement in all the matching conditions in the heavy Higgs boson limit.

We study the possibility of the scalar charmonium and glueball mixing in e + e − annihilation at s =10.6 GeV. The effects can be used to explain the unexpected large cross section (12±4 fb) and the anomalous angular distribution ( α =−1.1 +0.8 −0.6 ) of the exclusive e + e − → J / ψχ c 0 process observed by Belle experiments at KEKB. We calculate the helicity amplitudes for the process e + e − → J / ψH (0 ++ ) in NRQCD, where H (0 ++ ) is the mixed state. We present a detailed analysis on the total cross section and various angular asymmetries which could be useful to reveal the existence of the scalar glueball state.

We investigate the pseudoscalar transition form factors of nucleon for quasi-elastic scattering and \Delta resonance production in tau-neutrino nucleon scattering via the charged current interactions. Although the pseudoscalar form factors play an important role for the \tau production in neutrino-nucleon scattering, these are not known well. In this article, we examine their effects in quasi-elastic scattering and \Delta resonance production and find that the cross section, Q^{2} distribution, and spin polarization of the produced \tau^{\pm} leptons are quite sensitive to the pseudoscalar form factors., Comment: 7 pages, 3 figures

We study effects of heavy Higgs bosons on the top-pair production process at photon linear colliders. The interference patterns between the resonant Higgs-production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the $\gamma\gamma$--Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing top decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process $\gamma\gamma \to t \bar{t} \to (bW^+) (\bar{b}W^-) \to (b f_1 \bar{f}_2) (\bar{b} f_3 \bar{f}_4)$ are presented in terms of the generic $\gamma\gamma \to t \bar{t}$ production amplitudes.

Exclusive quarkonium pair production in electron-positron collisions is studied in non-relativistic QCD. The obtained cross section for J/\psi + \eta_c production in the leading order is confronted against the recent measurements by the Belle Collaboration at KEKB. It is shown that a large renormalization K-factor is necessary to explain the experimental data. We point out that the J^{PC}=0^{-+} nature of the hadronic systems that are assigned to be \eta_c should be tested by the triple angular distributions in terms of the scattering angle, and, polar and azimuthal angles of J/\psi into leptons. We further study J/\psi + J/\psi and \Upsilon + \Upsilon productions at LEP energies. Although the axial-vector couplings of the Z-boson to charm and bottom quarks allow production of such pairs when one of them is polarised transversally and the other longitudinally, we find that the integrated luminosity at Z pole accumulated by LEP is not large enough to observe the exclusive pair production of quarkonium., Comment: 11 pages, 2 eps figures, LaTeX

We calculate (g − 2)/2 of the muon, paying particular attention to the hadronic vacuum polarisation contribution and its uncertainties. The different data sets for each e + e − exclusive channel (as well as for the inclusive e + e − → hadrons channel) have been combined in order to produce the optimum estimate of the cross sections and their uncertainties. QCD sum rules are evaluated in order to resolve an apparent discrepancy between the inclusive data and the sum of the exclusive channels. We conclude

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter ξ and an improved estimate of the renormalization group invariant (RGI) bag constant B B q both entering into the B0d,s– B 0 d,s mass-differences. The averages of the results from the Laplace and moment sum rules to order αs are f B B B ≃(247±59) MeV and ξ≡ f B s B B s f B B B ≃(1.18±0.03) , in units where fπ=130.7 MeV. Combined with the experimental data on the mass-differences ΔMd,s, one obtains the constraint on the CKM weak mixing angle |Vts/Vtd|2⩾20.0(1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔMd, one predicts ΔMs=18.6(2.2) ps−1 in agreement with the present experimental lower bound and within the reach of Tevatron 2.

W bosons produced at high transverse momentum in hadron collisions can have polarization along the direction perpendicular to the production plane, which is odd under naive T reversal where both the three-momenta and angular momenta are reversed. Perturbative QCD predicts nonzero polarization at the one-loop level, which can be measured as parity-odd components in the angular distribution of charged leptons from the decay of W bosons. We perform a detector-level simulation with the generator MadGraph5-aMC@NLO, and demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20fb-1 of data. If confirmed, it will be the first experimental measurement of the sign of the imaginary part of one-loop QCD amplitudes.

The sensitivity of a huge underground water/ice Cherenkov detector, such as PINGU in IceCube, to the neutrino mass hierarchy, the atmospheric mixing angle and its octant, is studied in detail. Based on the event rate decomposition in the propagation basis, we illustrate the smearing effects from the neutrino scattering, the visible energy and zenith angle reconstruction procedures, the energy and angular resolutions, and the muon mis-identification rate, as well as the impacts of systematic errors in the detector resolutions, the muon mis-identification rate, and the overall normalization. The sensitivity, especially the mass hierarchy sensitivity, can be enhanced by splitting the muon-like events into two channels, according to the event inelasticity. We also show that including the cascade events can improve and stabilize the sensitivity of the measurements., Comment: 21 pages, 8 figures, 6 tables, to appear in JHEP

W bosons produced at high transverse momentum in hadron collisions can have polarization along the direction perpendicular to the production plane, which is odd under naïve T reversal where both the three-momenta and angular momenta are reversed. Perturbative QCD predicts nonzero polarization at the one-loop level, which can be measured as parity-odd components in the angular distribution of charged leptons from the decay of W bosons. We perform a detector-level simulation with the generator MadGraph5_aMC@NLO, and demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20 fb(-1) of data. If confirmed, it will be the first experimental measurement of the sign of the imaginary part of one-loop QCD amplitudes.

It has recently been pointed out that a component of the observed gamma ray emission in the low-latitudes of Fermi Bubble has a spectral shape that can be explained by a 10 GeV dark matter (DM) annihilating to tau leptons with a cross-section of 2 x 10^{-27} cm^3/s. Motivated by this possibility, we revisit the annihilation of a 10 GeV neutralino DM in the MSSM via stau exchange. The required stau masses and mixing, consistent with LEP direct search and electroweak precision constraints, are correlated with a possible enhancement of the Higgs decay rate to two photons. We also explore the implications of such a scenario for DM relic density and the muon anomalous magnetic moment, taking into account the recent ATLAS bounds on the chargino and the first two generation slepton masses, as well as the constraints on the Higgsino fraction of a 10 GeV neutralino., 30 pages, 5 figures; v2: added discussions on chargino mass bound from LHC, Higgs invisible decay constraints and vacuum stability

In this report I surveyed physics potential of the gamma-gamma option of a Linear e+e- Collider with the following questions in mind: What new discovery can be expected at a gamma-gamma collider in addition to what will be learned at its `parent' e+e- Linear Collider? By taking account of the hard energy spectrum and polarization of colliding photons, produced by Compton back-scattering of laser light off incoming e- beams, we find that a gamma-gamma collider is most powerful when new physics appears in the neutral spin-zero channel at an invariant mass below about 80% of the c.m. energy of the colliding e-e- system. If a light Higgs boson exists, its properties can be studied in detail, and if its heavier partners or a heavy Higgs boson exists in the above mass range, they may be discovered at a gamma-gamma collider. CP property of the scalar sector can be explored in detail by making use of linear polarization of the colliding photons, decay angular correlations of final state particles, and the pattern of interference with the Standard model amplitudes. A few comments are given for SUSY particle studies at a gamma-gamma collider, where a pair of charged spinless particles is produced in the s-wave near the threshold. Squark-onium may be discovered. An e^\pm gamma collision mode may measure the Higgs-Z-gamma coupling accurately and probe flavor oscillations in the slepton sector. As a general remark, all the Standard Model background simulation tools should be prepared in the helicity amplitude level, so that simulation can be performed for an arbitrary set of Stokes parameters of the incoming photon beams.

In view of the recent measurement of the muon g-2 and finalization of the LEP electroweak data, we re-examine all the new particle contributions to those observables in the MSSM. The SM fits the latest electroweak data excellently with the observed top-quark mass and the Higgs-boson mass of around 100 GeV, and so does the MSSM in the decoupling limit. The MSSM gives a slightly better fit to the data than the SM (\Delta \chi^2_{min} \sim -2) when relatively light left-handed sleptons of mass \sim 200 GeV and a light chargino of mixed higgsino-wino character (\mu/M_2 \sim 1) with mass \sim 100 GeV co-exist. The improvement in the fit diminishes quickly for wino- or higgsino- dominant charginos, for heavier charginos, and for lighter sleptons. We find that the MSSM contributions to the muon g-2 is most efficient when the light chargino has a mixed character. If \tan\beta < 10, the set of a light mixed chargino and light sleptons that is favored by the electroweak data is also favored by the g-2 data for \mu >0. Models with light gauginos (\mu/M_2 > 10) or light higgsinos (\mu/M_2 < 0.1) give significant contributions to muon g-2 only for large \tan\beta (\simgt 15)., Comment: 12 pages, latex, 4 figures. reference added. version to appear in Phys.Lett.B

We examine how accurately the general HZV couplings, with V=Z,gamma, may be determined by studying e^+e^- --> Hff-bar processes at future e^+e^- linear colliders. By using the optimal-observable method, which makes use of all available experimental information, we find out which combinations of the various HZV coupling terms may be constrained most efficiently with high luminosity. We also assess the benefits of measuring the tau-lepton helicities, identifying the bottom-hadron charges, polarizing the electron beam and running at two different collider energies. The HZZ couplings are generally found to be well constrained, even without these options, while the HZ-gamma couplings are not. The constraints on the latter may be significantly improved by beam polarization., 28 pages (LaTeX), 5 figures (axodraw and eps)

The minimal supersymmetric extension of standard model (MSSM) is examined by analyzing its quantum effects on the precision electroweak measurements and the muon g-2. We examine carefully the effects of light charginos and neutralinos that are found to improve the fit to the electroweak data. We identify two distinct regions on the $(\mu, M_2)$-plane that fit well to the electroweak data and give significant contribution to muon g-2., Comment: 13 pages, LaTeX2e, 6 eps-formated figures, remarks on b to s gamma, references and acknowledgement added, accepted for publication in Phys. Lett. B

The BRS invariance of the electroweak gauge theory leads to relationships between amplitudes with external massive gauge bosons and amplitudes where some of these gauge bosons are replaced with their corresponding Nambu-Goldstone bosons. Unlike the equivalence theorem, these identities are exact at all energies. In this paper we discuss such identities which relate the process $e^+e^- \to W^+W^-$ to $W^\pm\chi^\mp$ and $\chi^+\chi^-$ production. By using a general form-factor decomposition for $e^+e^- \to W^+W^-$, $e^+e^- \to W^\pm \chi^\mp$ and $e^+e^- \to \chi^+\chi^-$ amplitudes, these identities are expressed as sum rules among scalar form factors. Because these sum rules may be applied order by order in perturbation theory, they provide a powerful test of higher order calculations. By using additional Ward-Takahashi identities we find that the various contributions are divided into separately gauge-invariant subsets, the sum rules applying independently to each subset. After a general discussion of the application of the sum rules we consider the one-loop contributions of scalar-fermions in the Minimal Supersymmetric Standard Model as an illustration., Comment: 37 pages, including 16 figures

▪ Abstract The Large Electron Positron collider LEP1 at CERN produced tens of millions of Z bosons, and the e+e− linear collider SLC at SLAC has produced Z bosons with its polarized e− beam. Along with the measurements of the top-quark and W-boson masses at the Fermilab Tevatron [Formula: see text] collider, these Z-factory experiments have tested the standard electroweak theory with unprecedented precision. This chapter reviews the renormalizable gauge theory of the electroweak interactions and its quantum-level tests. Implications of the precision measurements are then studied within the standard model and its extentions.

We investigate the constraints on four-Fermi contact interactions from low-energy lepton-quark and lepton-lepton scattering experiments — polarization asymmetries in electron (muon)-nucleon scattering experiments, cesium and thallium atom parity violation measurements, neutrino-nuclei and neutrino-electron scattering experiments. These constraints are then combined by assuming the lepton and quark universalities and SU(2)L x U(l)y gauge invariance of the contact interaction, which leave independent six lepton-quark and three pure-leptonic interactions. Impacts of these constraints on models with an additional Z-boson are briefly discussed. We also present updates of the low-energy constraints on the S and T parameters.

The success of the quantum level predictions of the Standard Model on the $Z$ boson properties, on $\mw$ and on $\mt$, which makes use of the muon lifetime as an input, implies a stringent constraint on new physics contributions to the $V-A$ charged-current interactions among leptons. Observed unitarity of the CKM matrix elements then implies constraints on non-standard contributions to the lepton-quark charged-current interactions. By using the recent electroweak data as inputs, we find the 95%~CL limits for the corresponding contact interactions: $\Lambda_{CC,+}^{\ell\ell}>7.5$ TeV and $\Lambda_{CC,-}^{\ell\ell}>10.2$ TeV for the purely leptonic terms, and $\Lambda_{CC,+}^{\ell q}>5.8$ TeV and $\Lambda_{CC,-}^{\ell q}>10.1$~TeV for the lepton-quark contact interactions., Comment: 11 pages, Latex, 1 figure, added a few references

We update our previous work on an analysis of the electroweak data by including new and partly preliminary data available up to the 1996 summer conferences. The new results on the Z partial decay widths into b and c hadrons now offer a consistent interpretation of all data in the minimal standard model. The value extracted for the strong interaction coupling constant \alpha_s(mZ) agrees well with determinations in other areas. New constraints on the universal parameters S, T and U are obtained from the updated measurements. No signal of new physics is found in the S,T,U analysis once the SM contributions with mt \sim 175GeV and those of not a too heavy Higgs boson are accounted for. The naive QCD-like technicolor model is now ruled out at the 99%CL even for the minimal model with SU(2)_{TC}. In the absence of a significant new physics effect in the electroweak observables, constraints on masses of the top quark, mt, and Higgs boson, mH, are derived as a function of \alpha_s and the QED effective coupling $\bar{\alpha}(m_Z^2)$. The preferred range of mH depends rather strongly on the actual value of mt: mH130GeV for mt=180GeV at 95%CL. Prospects due to forthcoming improved measurements of asymmetries, the mass of the weak boson W mW, mt and $\bar{\alpha}(m_Z^2)$ are discussed. Anticipating uncertainties of 0.00020 for $\sbar^2(m_Z^2)$, 20MeV for mW, and 2GeV for mt, the new physics contributions to the S,T,U parameters will be constrained more severely, and, within the SM, the logarithm of the Higgs mass can be constrained to about +-0.35. The better constraints on S,T,U and on mH within the minimal SM should be accompanied with matching precision in $\bar{\alpha}(m_Z^2)$., Comment: 48 pages, Latex, uses axodraw.sty, 32 Postscript figures, to be published in Z.Phys.C