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Andrzej Czarnecki

Publications and source records attributed to Andrzej Czarnecki.

137 records · Page 8Linked to original sources
arXiv1995

Electroweak Fermion-loop Contributions to the Muon Anomalous Magnetic Moment

The two-loop electroweak corrections to the anomalous magnetic moment of the muon, generated by fermionic loops, are calculated. An interesting role of the top quark in the anomaly cancellation is observed. New corrections, including terms of order $G_μαm_t^2$, are computed and a class of diagrams previously thought to vanish are found to be important. The total fermionic correction is $-(23\pm 3) \times 10^{-11}$ which decreases the electroweak effects on $g-2$, predicted from one-loop calculations, by 12\%. We give an updated theoretical prediction for $g-2$ of the muon.

hep-ph↗
arXiv1995

Two-loop Light Quark Corrections To The Top Width

A method of computing two-loop fermionic contributions to the width of a heavy quark is described. An analytical formula for this effect in the limit of mass of the quark much larger than the decay products is obtained for the first time. The result confirms previous numerical studies.

hep-ph↗
arXiv1995

Recent Results on QCD Corrections to Semileptonic $b$-Decays

We summarize recent results on QCD corrections to various observables in semileptonic $b$ quark decays. For massless leptons in the final state we present effects of such corrections on triple differential distribution of leptons which are important in studies of polarized $b$ quark decays. Analogous formulas for distributions of neutrinos are applicable in decays of polarized $c$ quarks. In the case of decays with a $τ$ lepton in the final state mass effect of $τ$ has to be included. In this case we concentrate on corrections to the total decay width.

hep-ph↗
arXiv1994

Radiative corrections to $b\to cτ\batν_τ$

Analytical calculation is presented of the QCD radiative corrections to the rate of the process $b\to cτ\barν_τ$ and to the $τ$ lepton longitudinal polarization in $τ\barν_τ$ rest frame. The results are given in the form of one dimensional infrared finite integrals over the invariant mass of the leptons. We argue that this form may be optimal for phenomelogical applications due to a possible breakdown of semilocal hadron-parton duality in decays of heavy flavours.

hep-ph↗
arXiv1994

On the new method of computing two-loop massive diagrams

A recently proposed method of calculating scalar two-loop propagator and vertex functions with massive particles is illustrated with simple examples. A double integral representation is derived with the example of a propagator function. An analogous representation is used to compute the vertex function for space-like external momenta. Ways of dealing with divergent diagrams and of controlling the accuracy of the numerical evaluation of the two-loop functions are also discussed.

hep-ph↗
arXiv1994

New representation of two-loop propagator and vertex functions

We present a new method of calculating scalar propagator and vertex functions in the two-loop approximation, for arbitrary masses of particles. It is based on a double integral representation, suitable for numerical evaluation. Real and imaginary parts of the diagrams are calculated separately, so that there is no need to use complex arithmetics in the numerical program.

hep-ph↗
arXiv1994

A Precise Determination of $\tanβ$ from Heavy Charged Higgs Decay

We compute the energy spectrum of charged leptons in the decay $H^+\to \bar b+(t\to blν_l)$. The shape of the lepton spectrum obtained, and also the mean lepton energy, are sensitive to the handedness of the intermediate top quark. This sensitivity can be used to precisely determine $\tanβ$, a fundamental parameter of two Higgs doublet models.

hep-ph↗
arXiv1993

Two-loop renormalization group analysis of hadronic decays of a charged Higgs boson

We calculate next-to-leading QCD corrections to the decay $H^+ \to u\bar d$ for generic up and down quarks in the final state. A recently developed algorithm for evaluation of massive two-loop Feynman diagrams is employed to calculate renormalization constants of the charged Higgs boson. The origin and summation of large logarithmic corrections to the decay rate of the top quark into a lighter charged Higgs boson is also explained.

hep-ph↗
arXiv1993

Electroweak corrections to decays involving a charged Higgs boson

We present complete one-loop radiative corrections to the decay rate of a top quark into a charged Higgs boson and a bottom quark, and for the decay of a charged Higgs boson into leptons. The results are discussed in the framework of the two Higgs boson extension of the Standard Model suggested by supersymmetry. The effect of electroweak corrections after exclusion of universal corrections $Δr$ is found to decrease the partial width of the top quark typically by 5%.

hep-ph↗
arXiv1993

QCD corrections to the charged Higgs decay of a heavy quark

We present an analytic formula for the $O(α_s)$ corrections to the decay $t\to H^+b$ for nonzero $m_H$ and $m_b$. The Equivalence Theorem is used to relate these corrections to those for the process $t\to W^+b$. Contrary to previously published results we find that the effect of the $b$ quark mass is negligible for a wide range of $m_t$, $m_H$ and $\tan β$.

hep-ph↗