Christian Sturm

NLO Electroweak Corrections to Higgs Boson Production at Hadron Colliders

Results for the complete NLO electroweak corrections to Standard Model Higgs production via gluon fusion are included in the total cross section for hadronic collisions. Artificially large threshold effects are avoided working in the complex-mass scheme. The numerical impact at LHC (Tevatron) energies is explored for Higgs mass values up to 500 GeV (200 GeV). Assuming a complete factorization of the electroweak corrections, one finds a +5% shift with respect to the NNLO QCD cross section for a Higgs mass of 120 GeV both at the LHC and the Tevatron. Adopting two different factorization schemes for the electroweak effects, an estimate of the corresponding total theoretical uncertainty is computed.

Charm and Bottom Quark Masses: An Update

Using new four-loop results for the heavy quark vacuum polarization and new data for bottom quark production in electron-positron annihilation, an update on the determination of charm- and bottom-quark masses through sum rules has been performed. The previous result for the charm-quark mass,

NNLO computational techniques: The cases H→γγ and H→gg

{m}_{c}(3text{ }text{ }mathrm{GeV})=0.986(13)text{ }text{ }mathrm{GeV}

Higgs Pseudo-Observables, Second Riemann Sheet and All That

, based on the lowest moment, is supported by the new results from higher moments which lead to consistent values with comparable errors. The new value for the bottom quark,

Renormalization of quark bilinear operators in a momentum-subtraction scheme with a nonexceptional subtraction point

{m}_{b}(10text{ }text{ }mathrm{GeV})=3.610(16)text{ }text{ }mathrm{GeV}

Higgs production and decay with a fourth Standard-Model-like fermion generation

, corresponding to

Moments of heavy quark current correlators at four-loop order in perturbative QCD

{m}_{b}({m}_{b})=4.163(16)text{ }text{ }mathrm{GeV}

Two-Loop Threshold Singularities, Unstable Particles and Complex Masses

, makes use of both the new data and the new perturbative results and is consistent with the earlier determination.

Complete electroweak corrections to Higgs production in a Standard Model with four generations at the LHC

A large set of techniques needed to compute decay rates at the two-loop level are derived and systematized. The main emphasis of the paper is on the two Standard Model decays H → γγ and H → gg. The techniques, however, have a much wider range of application: they give practical examples of general rules for two-loop renormalization; they introduce simple recipes for handling internal unstable particles in two-loop processes; they illustrate simple procedures for the extraction of collinear logarithms from the amplitude. The latter is particularly relevant to show cancellations, e.g. cancellation of collinear divergencies. Furthermore, the paper deals with the proper treatment of non-enhanced two-loop QCD and electroweak contributions to different physical (pseudo-)observables, showing how they can be transformed in a way that allows for a stable numerical integration. Numerical results for the two-loop percentage corrections to H → γγ, gg are presented and discussed. When applied to the process pp → gg +X → H +X , the results show that the electroweak scaling factor for the cross section is between −4% and +6% in the range 100 GeV < M H < 500 GeV, without incongruent large effects around the physical electroweak thresholds, thereby showing that only a complete implementation of the computational scheme keeps two-loop corrections under control.

The relation between the QED charge renormalized in MSbar and on-shell schemes at four loops, the QED on-shell beta-function at five loops and asymptotic contributions to the muon anomaly at five and six loops

The relation between physical observables measured at LHC and Tevatron and standard model Higgs pseudo-observables (production cross section and partial decay widths) is revised by extensively using the notion of the Higgs complex pole on the second Riemann sheet of the S-matrix. The extension of their definition to higher orders is considered, confronting the problems that arise when QED (QCD) corrections are included in computing realistic observables. Numerical results are presented for pseudo-observables related to the standard model Higgs boson decay and production. The relevance of the result for exclusion plots of the standard model Higgs boson for high masses (up to 600 GeV) is discussed. Furthermore, a recipe for the analytical continuation of Feynman loop integrals from real to complex internal masses and complex Mandelstam invariants is thoroughly discussed.