602 research outputs found
in the Two Higgs Doublet Model up to Next-to-Next-to-Leading Order in QCD
We compute three-loop matching corrections to the Wilson coefficients
and in the Two Higgs Doublet Model by applying expansions for small,
intermediate and large charged Higgs boson masses. The results are used to
evaluate the branching ratio of to next-to-next-to
leading order accuracy, and to determine an updated lower limit on the charged
Higgs boson mass. We find \mhplus \ge 380 GeV at 95% confidence level when
the recently completed BABAR data analysis is taken into account. Our results
for the charged Higgs contribution to the branching ratio exhibit considerably
weaker sensitivity to the matching scale , as compared to previous
calculations.Comment: 20 pages, 15 figures; v2: minor modifications, matches published
version in JHE
Three-Loop Mixing of Dipole Operators
We calculate the complete three-loop O(alpha_s^3) anomalous dimension matrix
for the dimension-five dipole operators that arise in the Standard Model after
integrating out the top quark and the heavy electroweak bosons. Our computation
completes the three-loop anomalous dimension matrix of operators that govern
low-energy |Delta F| = 1 flavor-changing processes, and represents an important
ingredient of the next-to-next-to-leading order QCD analysis of the Bbar -> X_s
gamma decay.Comment: 4 pages, 1 figure; journal version, text below Eq. (7) correcte
Flavor changing effects on single charged Higgs boson production associated with a bottom-charm pair at CERN Large Hadron Collider
We study flavor changing effects on the \ppbchT process at the Large Hadron
Collider(LHC), which are inspired by the left-handed up-type squark mixings in
the Minimal Supersymmetric Standard Model(MSSM). We find that the SUSY QCD
radiative corrections to coupling can significantly enhance the cross
sections at the tree-level by a factor about with our choice of
parameters. We conclude that the squark mixing mechanism in the MSSM makes the
\ppbchT process a new channel for discovering a charged Higgs boson and
investigating flavor changing effects.Comment: One Latex file, 27 pages, 8 figures,to be appeared in PR
Tree-level contributions to B -> Xs gamma
Weak radiative decay B -> X_s gamma is known to be a loop-generated process.
However, it does receive tree-level contributions from CKM-suppressed b -> u
ubar s gamma transitions. In the present paper, we evaluate such contributions
together with similar ones from the QCD penguin operators. For a low value of
the photon energy cutoff E_0 ~ m_b/20 that has often been used in the
literature, they can enhance the inclusive branching ratio by more than 10%.
For E_0 = 1.6 GeV or higher, the effect does not exceed 0.4%, which is due to
phase-space suppression. Our perturbative results contain collinear logarithms
that depend on the light quark masses m_q (q=u,d,s). We have allowed m_b/m_q to
vary from 10 to 50, which corresponds to values of m_q that are typical for the
constituent quark masses. Such a rough method of estimation may be improved in
the future with the help of fragmentation functions once the considered effects
begin to matter in the overall error budget for BR(B -> X_s gamma).Comment: v3: Corrected factors of 2 in the subdominant T_3 contributions.
Minor changes in the numerical results (Table II
Exact Calculation of , \
We present an exact calculation of the Wilson coefficients
associated with the dipole moment operators. We also give an estimate of the
branching ratio for . We find that higher dimensional
effects are under control within for .Comment: 12 pages (plain TeX), 2 postscript figures available upon request.
UM-TH-93-20 , IP-ASTP-29-9
Effective Field Theories in R_xi gauges
In effective quantum field theories, higher dimensional operators can affect
the canonical normalization of kinetic terms at tree level. These contributions
for scalars and gauge bosons should be carefully included in the gauge fixing
procedure, in order to end up with a convenient set of Feynman rules. We
develop such a setup for the linear R_xi-gauges. It involves a suitable
reduction of the operator basis, a generalized gauge fixing term, and a
corresponding ghost sector. Our approach extends previous results for the
dimension-six Standard Model Effective Field Theory to a generic class of
effective theories with operators of arbitrary dimension.Comment: 16 pages, no figure
Using to Probe Top Quark Couplings
Possible anomalous couplings of the top-quark to on-shell photons and gluons
are constrained by the recent results of the CLEO Collaboration on both
inclusive and exclusive radiative decays. We find that the process \bsg\
can lead to reasonable bounds on both the anomalous electric and magnetic
dipole moments of the top-quark, while essentially no limits are obtained on
the corresponding chromoelectric and chromomagnetic moments, which enter the
expression for the decay rate only through operator mixing.Comment: 10 pages plus 6 figures (available by request), LaTex,
ANL-HEP-PR-93-3
Decay in Extensions of the Standard Model
The rare radiative decay is studied in extensions of the Standard Model. Matching conditions for
coefficients of operators appearing in the low energy effective Hamiltonian for
this process are derived, and QCD corrections to these coefficients are
analyzed. The decay rate is then calculated and compared with
the corresponding Standard Model result. We find that observable deviations
from Standard Model predictions can occur in theories for a reasonable range of parameter values.Comment: 17 pages with 5 figures not included but available upon request,
CALT-68-1893, TUM-T31-52/9
The transition in softly broken supersymmetry
We study the effect of supersymmetric contributions to the effective quark
transition , including leading order QCD effects. We apply
the discussion to the decay . Even though one-particle
irreducible contributions could play a role, numerical cancelations make the
amplitude for the two-photon emission strongly correlated to the
amplitude which is sharply constrained by experiment. A quite general statement
follows: as long as non-standard physics effects appear only in the matching of
the Wilson coefficients of the standard effective operator basis, the
deviations from the standard model expectations of the decay rates induced by
are bound to follow closely the corresponding deviations
on . Effects of new physics are therefore bound to be small.Comment: Latex2e, RevTex, 22 pages, 8 eps figures, comments and references
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