33 research outputs found
On the position of a heavy Higgs pole
Higher loop calculations in the Higgs sector of the standard model at the
Higgs mass scale have shown that perturbation theory diverges very badly at
about 1 TeV in the on-shell renormalization scheme. The prediction of the
position of the Higgs pole in the complex s-plane becomes unreliable. We show
that in the pole renormalization scheme this appears to have much better
convergence properties, while showing good agreement with the on-shell scheme
over the validity range of the latter. This suggests that the pole scheme
should be preferable for phenomenological studies of heavy Higgs bosons. We
discuss whether this behaviour can be the result of a certain relation between
the on-shell mass and the pole mass at the nonperturbative level.Comment: replaced by the published version, 12 pages LaTex, 3 eps figures
include
Nonperturbative three-point functions of the O(N) sigma model in the 1/N expansion at NLO
We present a calculation of the three-point functions of the O(N)-symmetric
sigma model. The calculation is done nonperturbatively by means of a
higher-order 1/N expansion combined with a tachyonic regularization which we
proposed in previous publications. We use the results for calculating the
standard model process ff -> H -> WW nonperturbatively in the quartic coupling
of the scalar sector
Muon colliders and the non-perturbative dynamics of the Higgs boson
A muon collider operating in the TeV energy range can be an ideal s-channel
Higgs boson factory. This is especially true for a heavy Higgs boson. The
non-perturbative dynamical aspects of such a Higgs boson were recently
investigated with large N expansion methods at next to leading order, and
reveal the existence of a mass saturation effect. Even at strong coupling, the
Higgs resonance remains always below 1 TeV. However, if the coupling is strong
enough, the resonance becomes impossible to be detected.Comment: Contributed to the International Conference on Physics Potential and
Development of mumu Colliders, December 15-17, 1999, San Francisco, C
Loops and legs beyond perturbation theory
Within the non-perturbative 1/N expansion, we discuss numerical methods for
calculating multi-loop Feynman graph needed to derive physical scattering
amplitudes. We apply higher order 1/N methods to the scalar sector of the
standard model, and show the existence of a mass saturation effect. The mass
saturation has direct implications for future searches at the LHC and at
possible muon colliders.Comment: Talk presented at the Loops and Legs in Quantum Field Theory 2000
meetin
New developments in the 1/N expansion and nonperturbative Higgs physics
We show in this paper that the 1/N expansion is a reliable tool to calculate
the properties of a heavy Higgs boson. The 1/N expansion sums up all orders in
perturbation theory, and therefore avoids the renormalization scheme dependence
of the conventional perturbative approach. It is explained how effects due to
the Landau pole of the Higgs sector are isolated and subtracted, and how to
perform actual calculations, by computing the Higgs line shape for the
processes f\bar f\to H \to ZZ,f'\bar f' at next-to-leading order in the 1/N
expansion. The results are compared to the perturbative results to show the
agreement between the perturbative and the nonperturbative approach for Higgs
masses up to 1 TeV. We conclude that the theoretical predictions for Higgs
observables are well under control for the entire kinematical region of the
LHC.Comment: 23 pages, latex, eps-figures include
Reduction and evaluation of two-loop graphs with arbitrary masses
We describe a general analytic-numerical reduction scheme for evaluating any
2-loop diagrams with general kinematics and general renormalizable
interactions, whereby ten special functions form a complete set after tensor
reduction. We discuss the symmetrical analytic structure of these special
functions in their integral representation, which allows for optimized
numerical integration. The process Z -> bb is used for illustration, for which
we evaluate all the 3-point, non-factorizable g^2*alpha_s mixed electroweak-QCD
graphs, which depend on the top quark mass. The isolation of infrared
singularities is detailed, and numerical results are given for all two-loop
three-point graphs involved in this process
Exact O(g^2 alpha_s) top decay width from general massive two-loop integrals
We calculate the b-dependent self-energy of the top quark at O(g^2 \alpha_s)
by using a general massive two-loop algorithm proposed in a previous article.
From this we derive by unitarity the O(\alpha_s) radiative corrections to the
decay width of the top quark, where all effects associated with the quark
mass are included without resorting to a mass expansion. Our results agree with
the analytical results available for the O(\alpha_s) correction to the top
quark width