Techniques for computing two-loop QCD corrections to b-->c transitions

We have recently presented the complete O(alpha_s^2) corrections to the semileptonic decay width of the b quark at maximal recoil. Here we discuss various technical aspects of that calculation and further applications of similar methods. In particular, we describe an expansion which facilitates the phase space integrations and the treatment of the mixed real-virtual corrections, for which Taylor expansion does not work and the so-called eikonal expansion must be employed. Several terms of the expansion are given for the O(alpha_s^2) QCD corrections to the differential semileptonic decay width of the b --quark at maximal recoil. We also demonstrate how the light quark loop corrections to the top quark decay rate can be obtained using the same methods. We briefly discuss the application of these techniques to the calculation of the O(alpha_s^2) correction to zero recoil sum rules for heavy flavor transitions.Comment: 22 pages, revte

Two-loop QCD corrections to semileptonic b decays at maximal recoil

We present a complete $O(\alpha_s^2)$ correction to the differential width of the inclusive semileptonic decay $b\to cl\nu_l$ at the kinematical point of vanishing invariant mass of the leptons, $q^2=0$. Together with the recently computed $O(\alpha_s^2)$ correction at the upper boundary of the lepton invariant mass spectrum, this new information permits an estimate of the $O(\alpha_s^2)$ effect in the total inclusive semileptonic decay width $b\to cl\nu_l$. We argue that the non-BLM part of the $O(\alpha_s^2)$ correction gives at most 1% correction to the inclusive semileptonic decay width $b\to cl\nu_l$. This significantly improves the credibility of extracting $|V_{cb}|$ from the inclusive semileptonic decays of the b-hadrons.Comment: 8 pages, revte

Electroweak interactions and the muon g-2: bosonic two-loop effects

We present a detailed evaluation of the bosonic two-loop electroweak corrections to the muon's anomalous magnetic moment. We study the Higgs mass dependence and find agreement with a previous evaluation in the large Higgs mass limit. We find $a_{\mu}^{\rm EW bos}({two-loop})=(-22.2 \pm 1.6)\times 10^{-11}$, for $114 {\rm GeV} \le M_{\rm Higgs}\le 700 {\rm GeV}$.Comment: 12 pages, 15 figure

Polarized Moller Scattering Asymmetries

The utility of polarized electron beams for precision electroweak studies is described. Parity violating Moller scattering asymmetries in e-e- --> e-e- are discussed. Effects of electroweak radiative corrections and the running sin^2(theta_W(Q^2)) are reviewed. The sensitivity of E158 (a fixed target e-e- experiment at SLAC) and future e-e- collider studies to ``new physics'' is briefly outlined.Comment: Updated Fig.

Threshold expansion for heavy-light systems and flavor off-diagonal current-current correlators

An expansion scheme is developed for Feynman diagrams describing the production of one massive and one massless particle near the threshold. As an example application, we compute the correlators of heavy-light quark currents, (\bar b gamma_mu u) and (\bar b gamma_5 u), through O(alpha_s^2).Comment: 4 pages, revtex

Photon-photon scattering: a tutorial

Long-established results for the low-energy photon-photon scattering, gamma gamma --> gamma gamma, have recently been questioned. We analyze that claim and demonstrate that it is inconsistent with experience. We demonstrate that the mistake originates from an erroneous manipulation of divergent integrals and discuss the connection with another recent claim about the Higgs decay into two photons. We show a simple way of correctly computing the low-energy gamma gamma scattering.Comment: 9 pages, 2 figures; v2: typographical errors corrected in eqs 1, 20, and 21; ref. [23] adde

A remark on the Brylinski conjecture for orbifolds

We present reformulation of Mathieu's result on representing cohomology classes of symplectic manifold with symplectically harmonic forms. We apply it to the case of foliated manifolds with transversally symplectic structure and to symplectic orbifolds. We obtain in particular that such representation is always possible for compact K\"{a}hler orbifolds.Comment: 10 page

Semi-Leptonic Decay of a Polarized Top Quark in the Noncommutative Standard Model

In this paper we study the noncommutative effects to the lepton spectrum from the decay of a polarized top quark. It is shown that the lowest contribution comes from the quadratic terms of the noncommutative parameter. The deviations from the standard model are significant for small values of the noncommutative characteristic scale. However, the charged lepton spin correlation coefficient has a remarkable deviation from the standard model from very low values of the noncommutative characteristic scale to 1 TeV.Comment: 8 pages, 4 figure