2,199 research outputs found
Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function
Starting from the known one-loop result for the -annihilation
process with
massless quarks we employ analyticity and crossing to determine the absorptive
parts of the corresponding one-loop contributions in Deep Inelastic Scattering
(DIS) and in the Drell-Yan process (DY). Whereas the
absorptive parts generate a non-measurable phase factor in the
-annihilation channel one obtains measurable phase effects from the
one-loop contributions in the deep inelastic and in the Drell-Yan case. We
compare our results with the results of previous calculations where the
absorptive parts in DIS and in the DY process were calculated directly in the
respective channels. We also present some new results on the dispersive and
absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.
QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.
We consider the small velocity sum rules for heavy flavour semileptonic
transitions that are used to estimate the zero recoil values of semileptonic
heavy flavour form factors. We analyze the complete O() radiative
correction to these sum rules. The corrections are universal and influence all
"model-independent" bounds previously derived for semileptonic form factors at
zero recoil.Comment: 13 pages, LaTeX, 3 figures
Two -loop radiative corrections to the Higgs decay width for large Higgs boson masses
This note is devoted to the calculation of the two-loop
radiative corrections to the Higgs decay width for large
values of the Higgs boson mass within the Minimal Standard Model.
The use of the Equivalence Theorem makes it possible to reduce the problem to
the consideration of the physical Higgs boson field and the Goldstone bosons
. We present analytical results for the various two- and
three-particle absorptive parts of two-loop contributions, using dispersive
techniques, analytic results for all but one of the dispersive contributions.
The typical size of the correction is percent for a Higgs boson
mass of order .Comment: 21 pages, 7 uuencoded figure
Inclusive Semileptonic Decays in QCD Including Lepton Mass Effects
Starting from an Operator Product Expansion in the Heavy Quark Effective
Theory up to order 1/m_b^2 we calculate the inclusive semileptonic decays of
unpolarized bottom hadrons including lepton mass effects. We calculate the
differential decay spectra d\Gamma/(dE_\tau ), and the total decay rate for B
meson decays to final states containing a \tau lepton.Comment: 16 pages + 4 figs. appended in uuencoded form, LaTeX, MZ-TH/93-3
Helicity Analysis of Semileptonic Hyperon Decays Including Lepton Mass Effects
Using the helicity method we derive complete formulas for the joint angular
decay distributions occurring in semileptonic hyperon decays including lepton
mass and polarization effects. Compared to the traditional covariant
calculation the helicity method allows one to organize the calculation of the
angular decay distributions in a very compact and efficient way. In the
helicity method the angular analysis is of cascade type, i.e. each decay in the
decay chain is analyzed in the respective rest system of that particle. Such an
approach is ideally suited as input for a Monte Carlo event generation program.
As a specific example we take the decay () followed by the nonleptonic decay for which we show a few examples of decay distributions which are
generated from a Monte Carlo program based on the formulas presented in this
paper. All the results of this paper are also applicable to the semileptonic
and nonleptonic decays of ground state charm and bottom baryons, and to the
decays of the top quark.Comment: Published version. 40 pages, 11 figures included in the text. Typos
corrected, comments added, references added and update
Quark and Pole Models of Nonleptonic Decays of Charmed Baryons
Quark and pole models of nonleptonic decays of charmed baryons are analysed
from the point of view of their symmetry properties. The symmetry structure of
the parity conserving amplitudes that corresponds to the contribution of the
ground-state intermediate baryons is shown to differ from the one hitherto
employed in the symmetry approach. It is pointed out that the "subtraction" of
sea quark effects in hyperon decays leads to an estimate of -exchange
contributions in charmed baryon decays that is significantly smaller than
naively expected on the basis of . An constraint questioning
the reliability of the factorization technique is exhibited. Finally, a
successful fit to the available data is presented.Comment: 25 pages, LATEX, 1643/PH IFJ Krako
SU(3)_flavor analysis of two-body weak decays of charmed baryons
We study two-body weak decays of charmed baryons \Lambda_c and \Xi_c into an
octet or decuplet baryon and a pseudoscalar meson employing the SU(3) flavor
symmetry. Using certain measured Cabibbo-favored modes, we fix the reduced
amplitudes and predict the branching ratios of various decays of charmed
baryons in the Cabibbo-enhanced, -suppressed and -doubly suppressed modes.Comment: 25 pages, No figure, Phys. Rev. D (to appear
Calculation of Infrared-Divergent Feynman Diagrams with Zero Mass Threshold
Two-loop vertex Feynman diagrams with infrared and collinear divergences are
investigated by two independent methods. On the one hand, a method of
calculating Feynman diagrams from their small momentum expansion extended to
diagrams with zero mass thresholds is applied. On the other hand, a numerical
method based on a two-fold integral representation is used. The application of
the latter method is possible by using lightcone coordinates in the parallel
space. The numerical data obtained with the two methods are in impressive
agreement.Comment: 20 pages, Latex with epsf-figures, References updated, to appear in
Z.Phys.
Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme
We give a general formulation of the quark-diagram scheme for the nonleptonic
weak decays of baryons. We apply it to all the decays of the antitriplet and
sextet charmed baryons and express their decay amplitudes in terms of the
quark-diagram amplitudes. We have also given parametrizations for the effects
of final-state interactions. For SU(3) violation effects, we only parametrize
those in the horizontal -loop quark diagrams whose contributions are solely
due to SU(3)-violation effects. In the absence of all these effects, there are
many relations among various decay modes. Some of the relations are valid even
in the presence of final-state interactions when each decay amplitude in the
relation contains only a single phase shift. All these relations provide useful
frameworks to compare with future experiments and to find out the effects of
final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are:
(i) some errors in the Tables and in the relations between the quark-diagram
amplitudes of this paper and those of Ref.[10] are corrected, (ii)
improvements are made in the presentation so that comparisons with previous
works and what have been done to include SU(3) breaking and final-state
interactions are more clearly stated; to appear in the Physical Review
Exclusive semileptonic and nonleptonic decays of the Bc meson
We study exclusive nonleptonic and semileptonic decays of the Bc-meson within
a relativistic constituent quark model previously developed by us. For the
nonleptonic decays we use the factorizing approximation. We update our model
parameters by using new experimental data for the mass and the lifetime of the
Bc meson and the leptonic decay constants of the D-meson. We calculate the
branching ratios for a large set of exclusive nonleptonic and semileptonic
decays of the meson and compare our results with the results of other
studies. As a guide for further experimental exploration we provide explicit
formulas for the full angular decay distributions in the cascade decays Bc^- =>
J/psi(=> l^+l^-) + rho^-(=> pi^- pi^0) and Bc^- => J/psi(=> l^+l^-) +
W^-(off-shell)(=> l^- + nubar).Comment: 19 pages, 2 figure
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