1,296 research outputs found
Techniques for computing two-loop QCD corrections to b-->c transitions
We have recently presented the complete O(alpha_s^2) corrections to the
semileptonic decay width of the b quark at maximal recoil. Here we discuss
various technical aspects of that calculation and further applications of
similar methods. In particular, we describe an expansion which facilitates the
phase space integrations and the treatment of the mixed real-virtual
corrections, for which Taylor expansion does not work and the so-called eikonal
expansion must be employed. Several terms of the expansion are given for the
O(alpha_s^2) QCD corrections to the differential semileptonic decay width of
the b --quark at maximal recoil. We also demonstrate how the light quark loop
corrections to the top quark decay rate can be obtained using the same methods.
We briefly discuss the application of these techniques to the calculation of
the O(alpha_s^2) correction to zero recoil sum rules for heavy flavor
transitions.Comment: 22 pages, revte
Two-loop QCD corrections to semileptonic b decays at maximal recoil
We present a complete correction to the differential width of
the inclusive semileptonic decay at the kinematical point of
vanishing invariant mass of the leptons, . Together with the recently
computed correction at the upper boundary of the lepton
invariant mass spectrum, this new information permits an estimate of the
effect in the total inclusive semileptonic decay width . We argue that the non-BLM part of the correction
gives at most 1% correction to the inclusive semileptonic decay width . This significantly improves the credibility of extracting
from the inclusive semileptonic decays of the b-hadrons.Comment: 8 pages, revte
Semi-Leptonic Decay of a Polarized Top Quark in the Noncommutative Standard Model
In this paper we study the noncommutative effects to the lepton spectrum from
the decay of a polarized top quark. It is shown that the lowest contribution
comes from the quadratic terms of the noncommutative parameter. The deviations
from the standard model are significant for small values of the noncommutative
characteristic scale. However, the charged lepton spin correlation coefficient
has a remarkable deviation from the standard model from very low values of the
noncommutative characteristic scale to 1 TeV.Comment: 8 pages, 4 figure
Threshold expansion for heavy-light systems and flavor off-diagonal current-current correlators
An expansion scheme is developed for Feynman diagrams describing the
production of one massive and one massless particle near the threshold. As an
example application, we compute the correlators of heavy-light quark currents,
(\bar b gamma_mu u) and (\bar b gamma_5 u), through O(alpha_s^2).Comment: 4 pages, revtex
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
Three-loop QCD corrections and b-quark decays
We present three-loop (NNNLO) corrections to the heavy-to-heavy quark
transitions in the limit of equal initial and final quark masses. In analogy
with the previously found NNLO corrections, the bulk of the result is due to
the beta_0^2 alpha_s^3 corrections. The remaining genuine three-loop effects
for the semileptonic b --> c decays are estimated to increase the decay
amplitude by 0.2(2)%. The perturbative series for the heavy-heavy axial current
converges very well.Comment: 5 page
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
is found to decrease the partial width of the top quark typically by
5%.Comment: 16 pages plus 11 figures available from the author upon request,
latex, Alberta Thy-29-9
Muon decay in orbit: spectrum of high-energy electrons
Experimental searches for lepton-flavor-violating coherent muon-to-electron
conversion in the field of a nucleus, have been proposed to reach the
unprecedented sensitivity of 10^(-16) - 10^(-18) per stopped muon. At that
level, they probe new interactions at effective-mass scales well beyond 1000
TeV. However, they must contend with background from ordinary bound muon decay.
To better understand the background-spectrum shape and rate, we have carried
out a detailed analysis of Coulombic-bound-state muon decay, including nuclear
recoil. Implications for future experiments are briefly discussed.Comment: 11 pages, 6 figures. Accepted for publication in Phys.Rev.D. v2: One
sentence modified to avoid possible misunderstandings. Journal versio
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