95 research outputs found
Exponentially Modified QCD Coupling
We present a specific class of models for an infrared-finite analytic QCD
coupling, such that at large space-like energy scales the coupling differs from
the perturbative one by less than any inverse power of the energy scale. This
condition is motivated by the ITEP Operator Product Expansion philosophy.
Allowed by the ambiguity in the analytization of the perturbative coupling, the
proposed class of couplings has three parameters. In the intermediate energy
region, the proposed coupling has low loop-level and renormalization scheme
dependence. The present modification of perturbative QCD must be considered as
a phenomenological attempt, with the aim of enlarging the applicability range
of the theory of the strong interactions at low energies.Comment: two references adde
The massless two-loop two-point function
We consider the massless two-loop two-point function with arbitrary powers of
the propagators and derive a representation, from which we can obtain the
Laurent expansion to any desired order in the dimensional regularization
parameter eps. As a side product, we show that in the Laurent expansion of the
two-loop integral only rational numbers and multiple zeta values occur. Our
method of calculation obtains the two-loop integral as a convolution product of
two primitive one-loop integrals. We comment on the generalization of this
product structure to higher loop integrals.Comment: 22 pages, revised version, eq. 9, 10 and 53 correcte
Neutrino Mixing Predictions of a Minimal SO(10) Model with Suppressed Proton Decay
During the past year, a minimal renormalizable supersymmetric SO(10) model
has been proposed with the following properties: it predicts a naturally stable
dark matter and neutrino mixing angles theta_atm and theta_13 while at the same
time accommodating CKM CP violation among quarks with no SUSY CP problem.
Suppression of proton decay for all allowed values of tan beta strongly
restricts the flavor structure of the model making it predictive for other
processes as well. We discuss the following predictions of the model in this
paper, e.g. down-type quark masses, and neutrino oscillation parameters, U_e3,
delta_MNSP, which will be tested by long baseline experiments such as T2K and
subsequent experiments using the neutrino beam from JPARC. We also calculate
lepton flavor violation and the lepton asymmetry of the Universe in this model.Comment: 22 pages, 11 figure
SUSY dark matter and lepton flavor violation
We study lepton flavor-violating (LFV) processes within a supersymmetric
type-I seesaw framework with flavor-blind universal boundary conditions,
properly accounting for the effect of the neutrino sector on the dark matter
relic abundance. We consider several possibilities for the neutrino Yukawa
coupling matrix and show that in regions of SUSY parameter space that yield the
correct neutralino relic density, LFV rates can differ from naive estimates by
up to two orders of magnitude. Contrary to common belief, we find that current
LFV limits do not exclude neutrino Yukawa couplings larger than top Yukawa
couplings. We introduce the ISAJET-M program that was used for the
computations.Comment: 37 pages, 9 figures, 6 tables. Version to appear in PR
Generalization of the BLM procedure and its scales in any order of pQCD
The Brodsky--Lepage--Mackenzie procedure is sequentially and unambiguously
extended to any fixed order of perturbative QCD beyond the so called
``large--\beta_0 approximation''. As a result of this procedure, the obtained
perturbation series looks like a continued-fraction representation. A
subsequent generalization of this procedure is developed, in order to optimize
the convergence of the final series, along the lines of the Fastest Convergence
Prescription. This generalized BLM procedure is applied to the Adler D function
and also to R_{e^+e^-} in QCD at NLO. A further extension of the sequential
BLM is presented which makes use of additional parameters to optimize the
convergence of the power-series at any fixed order of expansion.Comment: 24 pages, JHEP3, 4 figures are enclosed as eps-file, final version to
be published in JHE
Decays of Scalar and Pseudoscalar Higgs Bosons into Fermions: Two-loop QCD Corrections to the Higgs-Quark-Antiquark Amplitude
As a first step in the aim of arriving at a differential description of
neutral Higgs boson decays into heavy quarks, , to second
order in the QCD coupling , we have computed the
amplitude at the two-loop level in QCD for a general neutral Higgs boson which
has both scalar and pseudoscalar couplings to quarks. This amplitude is given
in terms of a scalar and a pseudoscalar vertex form factor, for which we
present closed analytic expressions in terms of one-dimensional harmonic
polylogarithms of maximum weight 4. The results hold for arbitrary
four-momentum squared, , of the Higgs boson and of the heavy quark mass,
. Moreover we derive the approximate expressions of these form factors near
threshold and in the asymptotic regime .Comment: 56 pages, 2 figure
New Uncertainties in QCD-QED Rescaling Factors using Quadrature Method
In this paper we briefly outline the quadrature method for estimating
uncertainties in a function of several variables and apply it to estimate the
numerical uncertainties in QCD-QED rescaling factors. We employ here the
one-loop order in QED and three-loop order in QCD evolution equations of
fermion mass renormalization. Our present calculations are found to be new and
also reliable compared to the earlier values employed by various authors.Comment: 14 page
Supersymmetric Higgs Yukawa Couplings to Bottom Quarks at next-to-next-to-leading Order
The effective bottom Yukawa couplings are analyzed for the minimal
supersymmetric extension of the Standard Model at two-loop accuracy within
SUSY-QCD. They include the resummation of the dominant corrections for large
values of tg(beta). In particular the two-loop SUSY-QCD corrections to the
leading SUSY-QCD and top-induced SUSY-electroweak contributions are addressed.
The residual theoretical uncertainties range at the per-cent level.Comment: 25 pages, 9 figures, added comments and references, typos corrected,
results unchanged, published versio
Wilson Expansion of QCD Propagators at Three Loops: Operators of Dimension Two and Three
In this paper we construct the Wilson short distance operator product
expansion for the gluon, quark and ghost propagators in QCD, including
operators of dimension two and three, namely, A^2, m^2, m A^2, \ovl{\psi} \psi
and m^3. We compute analytically the coefficient functions of these operators
at three loops for all three propagators in the general covariant gauge. Our
results, taken in the Landau gauge, should help to improve the accuracy of
extracting the vacuum expectation values of these operators from lattice
simulation of the QCD propagators.Comment: 20 pages, no figure
Standard Model Higgs-Boson Branching Ratios with Uncertainties
We present an update of the branching ratios for Higgs-boson decays in the
Standard Model. We list results for all relevant branching ratios together with
corresponding uncertainties resulting from input parameters and missing
higher-order corrections. As sources of parametric uncertainties we include the
masses of the charm, bottom, and top quarks as well as the QCD coupling
constant. We compare our results with other predictions in the literature.Comment: 32 pages, 4 figures, contribution to LHC Higgs Cross Section Working
Group https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections,
theoretical uncertainties for H->\mu\mu{} added, version to appear in
European Physical Journal
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