Pade-Improved Estimate of Perturbative Contributions to Inclusive Semileptonic b→ub\to u Decays

Pade-approximant methods are used to estimate the three-loop perturbative contributions to the inclusive semileptonic $b \to u$ decay rate. These improved estimates of the decay rate reduce the theoretical uncertainty in the extraction of the CKM matrix element $|V_{ub}|$ from the measured inclusive semileptonic branching ratio.Comment: 3 pages, latex, write-up of talk presented at DPF 200

The 4-loop quark mass anomalous dimension and the invariant quark mass

We present the analytical calculation of the four-loop quark mass anomalous dimension in Quantum Chromodynamics within the minimal subtraction scheme. On the basis of this result we find that the so-called invariant quark mass is a very good reference mass for the accurate evolution of the running MS-bar quark mass in phenomenological applications. We also obtain for the first time a complete 4-th order perturbative QCD expression for a physical quantity, the total Higgs boson decay rate into hadrons, and analyze the infrared fixed point for this case.Comment: 11 pages, Late

Virtual and Soft Pair Corrections to Polarized Muon Decay Spectrum

Radiative corrections to the muon decay spectrum due to soft and virtual electron--positron pairs are calculated.Comment: 10pp, 2 PS figs, details of calculations are adde

Semileptonic b --> u decays: lepton invariant mass spectrum

We compute O(alpha_s^2) QCD corrections to the lepton invariant mass spectrum in the decay b --> u l nu_l, relevant for the determination of the CKM matrix element |V_{ub}|. Our method can also be used to evaluate moments of the lepton energy distribution with an O(alpha_s^2) accuracy. The abelian part of our result gives the neutrino invariant mass spectrum in the muon decay and, upon integration, the O(alpha^2) correction to the muon lifetime.Comment: 5 pages, revte

Radiative corrections to muon decay in leading and next to leading approximation for electron spectrum

We have noted that the electron spectrum of muon decay in the leading logarithmic approximation calculated in two lowest orders of the perturbation theory in the paper of Berman (1958), can be reproduced by the parton language. This fact permits one to generalize the result to all orders of the perturbation theory using the structure function method.Comment: 4 pages, 1 figur

Asymptotic Pade-Approximant Methods and QCD Current Correlation Functions

Asymptotic Pade-approximant methods are utilized to estimate the leading-order unknown (i.e., not-yet-calculated) contributions to the perturbative expansions of two-current QCD correlation functions obtained from scalar-channel fermion and gluon currents, as well as from vector-channel fermion currents. Such contributions to the imaginary part of each correlator are polynomials of logarithms whose coefficients (other than the constant term within the polynomial) may be extracted from prior-order contributions by use of the renormalization-group (RG) equation appropriate for each correlator. We find surprisingly good agreement between asymptotic Pade-approximant predictions and RG-determinations of such coefficients for each correlation function considered, although such agreement is seen to diminish with increasing numbers of quark flavours. The RG-determined coefficients we obtain are then utilized in conjunction with asymptotic Pade-approximant methods to predict the RG-inaccessible constant terms of the leading-order unknown contributions for all three correlators. The vector channel predictions lead to estimates for the order $(\alpha_s^4)$ contribution to $R(s) \equiv[\sigma(e^+ e^- \to hadrons) / \sigma(e^+ e^- \to \mu^+ \mu^-)]$ for three, four, and five flavours.Comment: latex2e, 15 page

Group theory factors for Feynman diagrams

We present algorithms for the group independent reduction of group theory factors of Feynman diagrams. We also give formulas and values for a large number of group invariants in which the group theory factors are expressed. This includes formulas for various contractions of symmetric invariant tensors, formulas and algorithms for the computation of characters and generalized Dynkin indices and trace identities. Tables of all Dynkin indices for all exceptional algebras are presented, as well as all trace identities to order equal to the dual Coxeter number. Further results are available through efficient computer algorithms (see http://norma.nikhef.nl/~t58/ and http://norma.nikhef.nl/~t68/ ).Comment: Latex (using axodraw.sty), 47 page

Two-loop parameter relations between dimensional regularization and dimensional reduction applied to SUSY-QCD

The two-loop relations between the running gluino-quark-squark coupling, the gluino and the quark mass defined in dimensional regularization (DREG) and dimensional reduction (DRED) in the framework of SUSY-QCD are presented. Furthermore, we verify with the help of these relations that the three-loop beta-functions derived in the minimal subtraction scheme combined with DREG or DRED transform into each other. This result confirms the equivalence of the two schemes through three-loops, if applied to SUSY-QCD.Comment: 14 pages, Latex; v2 matches published versio

Quark Mass Anomalous Dimension to alpha_s**4

We present the results of analytic calculation of the quark mass anomalous dimension to alpha_s**4.Comment: 7 pages, LaTeX; elsart.sty is used (included