1,813 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
Stability of tetrons
We consider the interactions in a mesonic system, referred here to as
`tetron', consisting of two heavy quarks and two lighter antiquarks (which may
still be heavy in the scale of QCD), i.e. generally , and study the existence of bound states below the threshold for decay
into heavy meson pairs. At a small ratio of the lighter to heavier quark masses
an expansion parameter arises for treatment of the binding in such systems. We
find that in the limit where all the quarks and antiquarks are so heavy that a
Coulomb-like approximation can be applied to the gluon exchange between all of
them, such bound states arise when this parameter is below a certain critical
value. We find the parametric dependence of the critical mass ratio on the
number of colors , and confirm this dependence by numerical calculations.
In particular there are no stable tetrons when all constituents have the same
mass. We discuss an application of a similar expansion in the large limit
to realistic systems where the antiquarks are light and their interactions are
nonperturbative. In this case our findings are in agreement with the recent
claims from a phenomenological analysis that a stable
tetron is likely to exist, unlike those where one or both bottom quarks are
replaced by the charmed quark.Comment: 10 pages, 2 figure
V-a Tests Through Leptons from Polarised Top Quarks
Angular-energy distributions are studied for charged leptons and neutrinos
from the decays of polarised top quarks. A small admixture of V+A interactions
is incorporated. The polarisation dependent part of the neutrino distribution
which can be measured experimentally through the missing momentum is
particularly sensitive towards deviations from the V-A structure. This result
remains unaffected by QCD corrections which, however, cannot be neglected in a
quantitative analysis.Comment: 10 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded ps
files). A complete postscript file, including figures, is available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/ttp94-4/ttp94-4.ps, Local preprint# TTP94-
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
Theoretical pressure distributions over arbitrarily shaped periodic waves in subsonic compressible flow and comparison with experiment
Theoretical solution for pressure distribution over arbitrarily shaped periodic waves using Fourier serie
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