Production and decay of the Standard Model Higgs Bososn at LEP200

We collect and update theoretical predictions for the production rate and decay branching fractions of the Standard Model Higgs boson that will be relevant for the Higgs search at LEP200. We make full use of the present knowledge of radiative corrections. We estimate the systematics arising from theoretical and experimental uncertainties.Comment: 27 page

Elimination of Threshold Singularities in the Relation Between On-Shell and Pole Widths

In a previous communication by two of us, Phys. Rev. Lett. 81, 1373 (1998), the gauge-dependent deviations of the on-shell mass and total decay width from their gauge-independent pole counterparts were investigated at leading order for the Higgs boson of the Standard Model. In the case of the widths, the deviation was found to diverge at unphysical thresholds, m_H = 2 root{xi_V} m_V (V = W,Z), in the R_xi gauge. In this Brief Report, we demonstrate that these unphysical threshold singularities are properly eliminated if a recently proposed definition of wave-function renormalization for unstable particles is invoked.Comment: 8 pages (Latex), 1 figure (Postscript

Two-Loop O(αsGFmt2){\cal O}(\alpha_sG_Fm_t^2) Corrections to the Fermionic Decay Rates of the Standard-Model Higgs Boson

Low- and intermediate mass Higgs bosons decay preferably into fermion pairs. The one-loop electroweak corrections to the respective decay rates are dominated by a flavour-independent term of ${\cal O}(G_Fm_t^2)$. We calculate the two-loop gluon correction to this term. It turns out that this correction screens the leading high-$m_t$ behaviour of the one-loop result by roughly 10\%. We also present the two-loop QCD correction to the contribution induced by a pair of fourth-generation quarks with arbitrary masses. As expected, the inclusion of the QCD correction considerably reduces the renormalization-scheme dependence of the prediction.Comment: 14 pages, latex, figures 2-5 appended, DESY 94-08

Quarkonium production in deep-inelastic scattering

We discuss the inclusive production of J/psi mesons in deep-inelastic scattering (DIS) via the electromagnetic, weak neutral, and charged currents within the factorization formalism of nonrelativistic quantum chromodynamics. Theoretical predictions are confronted with experimental data of e p and nu N DIS taken by the H1 Collaboration at DESY HERA and the CHORUS Collaboration at CERN, respectively.Comment: 6 pages (Latex), 6 figures (Postscript); to appear in the Proceedings of the 6th International Symposium on Radiative Corrections: Application of Quantum Field Theory to Phenomenology (RADCOR 2002), Kloster Banz, Germany, September 8-13, 200

Two-Loop Static QCD Potential for General Colour State

In this letter, we extend the known results for the QCD potential between a static quark and its antiquark by computing the two-loop corrections to the colour-octet state.Comment: 7 page

Heavy-Higgs Lifetime at Two Loops

The Standard-Model Higgs boson with mass $M_H >> 2M_Z$ decays almost exclusively to pairs of $W$ and $Z$ bosons. We calculate the dominant two-loop corrections of $O( G_F^2 M_H^4 )$ to the partial widths of these decays. In the on-mass-shell renormalization scheme, the correction factor is found to be $1 + 14.6$, where the second term is the one-loop correction. We give full analytic results for all divergent two-loop Feynman diagrams. A subset of finite two-loop vertex diagrams is computed to high precision using numerical techniques. We find agreement with a previous numerical analysis. The above correction factor is also in line with a recent lattice calculation.Comment: 26 pages, 6 postscript figures. The complete paper including figures is also available via WWW at http://www.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/TUM-HEP-247-96.ps.g

Two-Loop O(alpha_s G_F M_Q^2) Heavy-Quark Corrections to the Interactions between Higgs and Intermediate Bosons

By means of a low-energy theorem, we analyze at O(alpha_s G_F M_Q^2) the shifts in the Standard-Model W^+W^-H and ZZH couplings induced by virtual high-mass quarks, Q, with M_Q >> M_Z, M_H, which includes the top quark. Invoking the improved Born approximation, we then find the corresponding corrections to various four- and five-point Higgs-boson production and decay processes which involve the W^+W^-H and ZZH vertices with one or both of the gauge bosons being connected to light-fermion currents, respectively. This includes e^+e^- -> f anti-f H via Higgs-strahlung, via W^+W^- fusion (with f = nu_e), and via ZZ fusion (with f = e), as well as H -> 2V -> 4f (with V = W, Z).Comment: 20 pages (Latex); Physical Review D (to appear

Irrational constants in positronium decays

We establish irrational constants, that contribute to the positronium lifetime at $O(\alpha)$ and $O(\alpha^2)$ order. In particular we show, that a new type of constants appear, which are not related to Euler--Zagier sums or multiple $\zeta$ values.Comment: Presented at 9th Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory, Sondershausen, 20-25 Apr 2008. 6 pages, 3 figure

Renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions

We obtain the next-to-next-to-leading-log renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions by using potential NRQED. These results can also be applied to the computation of the muonic Hydrogen spectrum where we are able to reproduce some known double logs at O(m\alpha^6). We compare with other formalisms dealing with log resummation available in the literature.Comment: 9 pages, LaTeX. Minor changes, note added, final versio

Inclusive Production of Single Hadrons with Finite Transverse Momenta in Deep-Inelastic Scattering at Next-to-Leading Order

We calculate the cross section for the inclusive production of single hadrons with finite transverse momenta in deep-inelastic scattering at next-to-leading order (NLO), i.e. through O(alpha_s^2), in the parton model of QCD endowed with non-perturbative parton distribution functions (PDFs) and fragmentation functions (FFs). The NLO correction is found to produce a sizeable enhancement in cross section, of up to one order of magnitude, bringing the theoretical prediction to good agreement with recent measurements for neutral pions and charged hadrons at DESY HERA. This provides a useful test for the universality and the scaling violations of the FFs predicted by the factorization theorem. Such comparisons can also be used to constrain the gluon PDF of the proton.Comment: 26 pages, 12 figure