444 research outputs found
Virtual Top-Quark Effects on the H->bb-bar Decay at Next-to-Leading Order in QCD
By means of a heavy-top-quark effective Lagrangian, we calculate the
three-loop corrections of O(alpha_s^2 G_F M_t^2) to the H->bb-bar partial decay
width of the standard-model Higgs boson with intermediate mass M_H<<2M_t. We
take advantage of a soft-Higgs theorem to construct the relevant coefficient
functions. We present our result both in the MS-bar and on-shell schemes of
mass renormalization. The MS-bar formulation turns out to be favourable with
regard to the convergence behaviour. We also test a recent idea concerning the
naive non-abelianization of QCD.Comment: 8 pages (Latex), 5 figures (Postscript
Production and decay of the Standard Model Higgs Bososn at LEP200
We collect and update theoretical predictions for the production rate and
decay branching fractions of the Standard Model Higgs boson that will be
relevant for the Higgs search at LEP200. We make full use of the present
knowledge of radiative corrections. We estimate the systematics arising from
theoretical and experimental uncertainties.Comment: 27 page
Electroweak corrections to -boson hadroproduction at finite transverse momentum
We calculate the full one-loop electroweak radiative corrections, of , to the cross section of single -boson inclusive
hadroproduction at finite transverse momentum (). This includes the corrections to production, the
corrections to production, and certain QCD-electroweak interference
contributions involving a single quark trace. We recover the QCD and purely
weak corrections and study the QED corrections and the QCD-electroweak
interference contributions for the first time. We also consider direct and
resolved photoproduction in elastic and inelastic scattering. We present
and rapidity distributions for the experimental conditions at the Fermilab
Tevatron and the CERN LHC and assess the significance of the various
contributions.Comment: 31 pages, 11 figures; discussion enhanced, figures added, references
added and updated; accepted for publication in Nucl. Phys.
A New Renormalization Scheme of Fermion Fields in Electroweak Standard Model
This paper has been withdrawn by the author,due a immature idea.Comment: 6 page
Two-Loop Corrections to the Fermionic Decay Rates of the Standard-Model Higgs Boson
Low- and intermediate mass Higgs bosons decay preferably into fermion pairs.
The one-loop electroweak corrections to the respective decay rates are
dominated by a flavour-independent term of . We calculate
the two-loop gluon correction to this term. It turns out that this correction
screens the leading high- behaviour of the one-loop result by roughly
10\%. We also present the two-loop QCD correction to the contribution induced
by a pair of fourth-generation quarks with arbitrary masses. As expected, the
inclusion of the QCD correction considerably reduces the renormalization-scheme
dependence of the prediction.Comment: 14 pages, latex, figures 2-5 appended, DESY 94-08
A critical phenomenological study of inclusive photon production in hadronic collisions
We discuss fixed target and ISR inclusive photon production and attempt a
comparison between theory and experiments. The dependence of the theoretical
predictions on the structure functions, and on the renormalization and
factorization scales is investigated. The main result of this study is that the
data cannot be simultaneously fitted with a single set of scales and structure
functions. On the other hand, there is no need for an additional intrinsic
to force the agreement between QCD predictions and experiments, with
the possible exception of one data set. Since the data cover almost overlapping
kinematical ranges this raises the question of consistency among data sets. A
comparative discussion of some possible sources of experimental uncertainties
is sketched.Comment: 22 pages, 3 tables, 10 figures, Late
Polarization of Prompt J/psi at the Tevatron
The polarization of prompt J/psi at the Fermilab Tevatron is calculated
within the nonrelativistic QCD factorization framework. The contribution from
radiative decays of P-wave charmonium states decreases, but does not eliminate,
the transverse polarization at large transverse momentum. The angular
distribution parameter alpha for leptonic decays of the J/\psi is predicted to
increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. The
prediction is consistent with measurements by the CDF Collaboration at
intermediate values of p_T, but disagrees by about 3 standard deviations at the
largest values of p_T measured.Comment: 4 pages, 2 figures, one reference added, accepted for publication in
Phys. Rev.
Heavy-Higgs Lifetime at Two Loops
The Standard-Model Higgs boson with mass decays almost
exclusively to pairs of and bosons. We calculate the dominant two-loop
corrections of to the partial widths of these decays. In
the on-mass-shell renormalization scheme, the correction factor is found to be
, where the second term is the
one-loop correction. We give full analytic results for all divergent two-loop
Feynman diagrams. A subset of finite two-loop vertex diagrams is computed to
high precision using numerical techniques. We find agreement with a previous
numerical analysis. The above correction factor is also in line with a recent
lattice calculation.Comment: 26 pages, 6 postscript figures. The complete paper including figures
is also available via WWW at
http://www.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/TUM-HEP-247-96.ps.g
Associated Production of Heavy Quarkonia and Electroweak Bosons at Present and Future Colliders
We investigate the associated production of heavy quarkonia, with
angular-momentum quantum numbers ^{2S+1}L_J = ^1S_0, ^3S_1, ^1P_1, ^3P_J (J =
0, 1, 2), and photons, Z bosons, and W bosons in photon-photon, photon-hadron,
and hadron-hadron collisions within the factorization formalism of
nonrelativistic quantum chromodynamics providing all contributing partonic
cross sections in analytic form. In the case of photoproduction, we also
include the resolved-photon contributions. We present numerical results for the
processes involving J/psi and chi_{cJ} mesons appropriate for the Fermilab
Tevatron, CERN LHC, DESY TESLA, operated in the e^+ e^- and gamma gamma modes,
and DESY THERA.Comment: 41 pages (Latex), 10 figures (Postscript
Associated Production of Bottomonia and Higgs Bosons at Hadron Colliders
We study the associated production of bottomonia and Higgs bosons at hadron
colliders within the factorization formalism of nonrelativistic quantum
chromodynamics providing all contributing partonic cross sections in analytic
form. While such processes tend to be suppressed in the standard model, they
may have interesting cross sections in its minimal supersymmetric extension,
especially at large values of tan(beta), where the bottom Yukawa couplings are
enhanced. We present numerical results for the processes involving the lighter
CP-even h^0 boson and the CP-odd A^0 boson appropriate for the Fermilab
Tevatron and the CERN LHC.Comment: 33 pages, 7 figures, Latex, to appear in Phys. Rev.
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