Ref Arxiv: hep-ph/0108065
Ref. & Cit.: NASA ADS
Résumé:

We present a new independent evaluation of the hadronic and QCD contributions to the QED running coupling \alpha(M_Z) and to the muonium hyperfine splitting \nu. We obtain: \Delta\alpha_{had}=2770(17)10^{-5} and \Delta\nu_{had}=232.5(2.5) Hz. Combined with the QED and Electroweak Standard Model contributions, they lead to: \alpha^{-1}(M_Z)=128.926(25) and to the Fermi energy splitting \nu_F=4~459~031~783(229) Hz, where for the latter, we have used, in addition, the precise measurement of the muonium hyperfine splitting \nu_{exp}. We use \nu_F in order to predict the ratios of masses m_{\mu}/m_e=206.768~276(11) and of the magnetic moments \mu_{\mu}/\mu^e_B=4.841~970~47(25)10^{-3}, which are in excellent agreement with the ones quoted by the Particle Data Group. These remarkable agreements can provide strong constraints on some contributions beyond the Standard Model.

Ref Arxiv: hep-ph/0104205
DOI: 10.1103/PhysRevD.64.053018
Ref. & Cit.: NASA ADS
13 citations
Résumé:

We compute the leading logarithm electroweak contributions to γγ→ff̅ processes in the standard model and minimal supersymmetric standard model. Several interesting properties are pointed out, such as the importance of the angular dependent terms, of the Yukawa terms, and especially of the tan2β dependence in the supersymmetry contributions. These properties are complementary to those found in e+e-→ff̅. These radiative correction effects should be largely observable at future high energy γγ colliders. Polarized beams would give interesting checks of the structure of the one-loop corrections. We finally discuss the need for two-loop calculations and resummation.

Ref Arxiv: hep-ph/0104245
DOI: 10.1103/PhysRevD.64.053016
Ref. & Cit.: NASA ADS
17 citations
Résumé:

We consider the process of top-quark–top-antiquark production from electron-positron annihilation, for center-of-mass energies in the few TeV regime, in the minimal supersymmetric standard model theoretical framework. We show that, at the one loop level, the variations of a number of observable quantities with energy (slopes) in a region of about 3 TeV are only dependent on tan β. Under optimal experimental conditions, a combined measurement of these slopes might identify tan β values in a range tan β<2, tan β>20 with acceptable precision.

Ref Arxiv: hep-ph/0205092
DOI: 10.1016/S0370-2693(02)02133-0
Ref. & Cit.: NASA ADS
16 citations
Résumé:

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter \xi and an improved estimate of the renormalization group invariant (RGI) bag constant \hat{B}_{B_q} both entering into the B^0_{d,s} - \bar{B}^0_{d,s} mass-differences. The averages of the results from the Laplace and moment sum rules to order \alpha_s are f_B\sqrt{\hat B_B} \simeq (247 \pm 59) MeV and \xi \equiv f_{B_s} \sqrt{\hat B_{B_s}} / f_{B} \sqrt{\hat B_{B}} \simeq (1.18\pm 0.03), in units where f_\pi=130.7 MeV. Combined with the experimental data on the mass-differences \Delta M_{d,s}, one obtains the constraint on the CKM weak mixing angle |V_{ts}/V_{td}|^2 > 20.0 (1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on \Delta M_d, one predicts \Delta M_s=18.6 (2.2) ps^{-1} in agreement with the present experimental lower bound and within the reach of Tevatron 2.

Ref Arxiv: hep-ph/0103335
DOI: 10.1103/PhysRevD.64.073008
Ref. & Cit.: NASA ADS
26 citations
Résumé:

We consider the separate effects on four-fermion processes, in the TeV energy range, produced at one loop by Sudakov logarithms of universal and nonuniversal kind, working in the ’t Hooft ξ=1 gauge. Summing the various vertex and box contributions allows us to isolate two quite different terms. The first one is a combination of vertex and box quadratic and linear logarithms that are universal and independent of the scattering angle θ. The second one is θ dependent, not universal, linearly logarithmic, and produced only by weak boxes. We show that for several observables, measurable at future linear e+e- colliders, the role of the latter term is dominant, and we discuss the implications of this fact for what concerns the reliability of a one-loop approximation.

Ref Arxiv: hep-ph/0103199
DOI: 10.1016/S0370-2693(01)00743-2
Ref. & Cit.: NASA ADS
90 citations
Résumé:

We present a new independent evaluation of the hadronic vacuum polarization contributions a_l{had}(l.o)=(1/2)(g-2)_l{had}(l.o) to the anomalous magnetic moment (anomaly) of the muon and tau leptons using tau-decays and e+e- data. The alone theoretical input used for describing the high-energy region not accessible experimentally is perturbative QCD plus (negligible) additional effects due to the QCD vacuum condensates. We obtain: a_mu{had}(l.o)= 7020.6(75.6)10^{-11} and a_tau{had}(l.o)= 353.6(3.8)10^{-8}, which we compare with previous determinations. Our analysis leads to the Standard Model (SM) prediction: a_mu^{SM}=116~591~846.9(78.9)10^{-11}.Confronting a_mu^{SM} with the recent BNL measurement leads to a_mu{new}= a_mu{exp}-a_mu{SM}=176(170)10^{-11}. Combined with the mean existing determinations of a_mu^{had}(l.o), this leads to the conservative range: -42 < a_mu{new}10^{11} < 413 at 90% CL, from which we derive conservative lower bounds on the scales of some new physics. We also update our old predictions of the SM contributions to a_tau. Including QED to sixth order, higher order hadronic and electroweak contributions, we obtain a_tau{SM}=117 755(7)10^{-8}, waiting for a future precise measurement of a_tau.

Commentaires: Referred to by:Erratum to: “Muon and tau anomalies updated”: [Phys. Lett. B 513 (2001) 53], Physics Letters B, Volume 526, Issues 3-4, 7 February 2002, Pages 414-415

Ref Arxiv: hep-ph/0103135
DOI: 10.2001EPJC...20..659G
Ref. & Cit.: NASA ADS
Résumé:

The process $\gamma\gamma\to Z H $ first arises at the one loop level, and as such it provides us with remarkable tests of the structure of the electroweak Higgs sector. These tests are complementary to those in the gauge sector involving $\gamma\gamma\to \gamma\gamma, \gamma Z, ZZ$. We show that in the standard model (SM) where H=HSM, as well as in the supersymmetric case where H=h0, H0 or A0, observables exist (like e.g. the energy dependence, angular distribution, photon polarization dependence or final Z polarization) which present rather spectacular properties. Such properties involve strong threshold effects with steps, bumps or peaks, reflecting the type of Higgs and heavy quarks and chargino masses and couplings predicted by the SM and supersymmetric models.