Biomedical subjects

J H Kühn

Publications and source records attributed to J H Kühn.

4 recordsLinked to original sources

PubMed2006

Four-loop QCD corrections to the electroweak rho parameter.

The four-loop QCD corrections to the electroweak rho parameter arising from top and bottom quark loops are computed. Specifically we evaluate the missing "nonsinglet" piece. Using algebraic methods the amplitude is reduced to a set of around 50 new master integrals which are calculated with various analytical and numerical methods. The inclusion of the newly completed term halves the final value of the four-loop correction for the minimally renormalized top-quark mass. The predictions for the shift of the weak mixing angle and the W-boson mass are thus stabilized.

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PubMed2006

Scalar correlator at [symbol: see text](alpha(s)4), Higgs boson decay into bottom quarks, and bounds on the light-quark masses.

We compute, for the first time, the absorptive part of the massless correlator of two quark scalar currents in five loops. As physical applications, we consider the [symbol: see text](alpha(s)4) corrections to the decay rate of the standard model Higgs boson into quarks, as well as the constraints on the strange quark mass following from QCD sum rules.

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PubMed2005

Strange-quark mass from tau-lepton decays with O(alpha3s) accuracy.

The first complete calculation of the quadratic quark mass correction to the correlator of the two currents relevant for the strangeness-changing semihadronic tau-decay rate is presented including its real part at the four-loop level. This allows us to perform the extraction of the strange-quark mass m(s) from the decay width of the tau-lepton with full O(alpha3s) accuracy. In agreement with previous estimates, the newly computed alpha3s term proves to be rather large. This justifies inclusion of the similarly estimated alpha4s term in phenomenological analysis. Combined with an updated value of V us and an "improved" version of the renormalization group improvement of the perturbative series, this leads to an increase of the central value of m(s) by about 20% and a partial reduction of the theoretical uncertainty by about 50%.

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PubMed2001

Cross section of e(+)e(-) annihilation into hadrons of order alpha(4)(s)n(2)(f) in perturbative QCD.

We present the first genuine QCD five-loop calculation of the vacuum polarization functions: analytical terms of order alpha(4)(s)n(2)(f) to the absorptive parts of vector and scalar correlators. These corrections form an important gauge-invariant subset of the full omicron(alpha(4)(s)) correction to e(+)e(-) annihilation into hadrons and the Higgs decay rate into hadrons, respectively. They discriminate between different widely used estimates of the full result.

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