266 research outputs found
Precise predictions for Higgs production in models with color-octet scalars
We describe an effective-theory computation of the next-to-next-to-leading
order (NNLO) QCD corrections to the gluon-fusion production of a Higgs boson in
models with massive color-octet scalars in the (8,1)_0 representation.
Numerical results are presented for both the Tevatron and the LHC. The
estimated theoretical uncertainty is greatly reduced by the inclusion of the
NNLO corrections. Color-octet scalars can increase the Standard Model rate by
more than a factor of two in allowed regions of parameter space.Comment: 6 pages, 5 figures, to appear in the proceedings of the "10th DESY
Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field
Theory", Woerlitz, Germany, April 25-30, 201
Four-Loop Tadpoles: Applications in QCD
Recent applications of single-scale four-loop tadpoles are briefly reviewed.
An algorithm for the evaluation of current correlators based on differential
equations is described and applied to obtain high moments of the vacuum
polarization function at O(alphas^2) as a preparation of O(alphas^3)
calculations.Comment: 5 pages, 1 figure, to appear in the proceedings of the 8th DESY
Workshop on Elementary Particle Theory, Loops and Legs in Quantum Field
Theory, April 23-28, 2006, Eisenach, German
Charm and Bottom Quark Masses from Perturbative QCD
Using a new result for the first moment of the hadronic production cross
section at order , and new data on the and
resonances for the charm quark, we determine the \msb masses of the
charm and bottom quarks to be GeV and
GeV. We assume that the continuum
contribution to the sum rules is adequately described by pQCD. While we observe
a large reduction of the perturbative error, the shifts induced by the
theoretical input are very small. The main change in the central value of
is related to the experimental data. On the other hand, the value of is
not changed by our calculation to the assumed precision.Comment: 5 pages, 2 figures, final version as publishe
Single Scale Tadpoles and O(GF mt^2 as^3) Corrections to the rho Parameter
We present a new set of high precision numerical values of four-loop
single-scale vacuum integrals, which we subsequently use to obtain the
non-singlet corrections to the rho parameter at O(GF mt^2 as^3). Our result for
Delta rho is in agreement with the recent calculation [1].Comment: 20 pages, references added, final version as published in journa
The impact of the LHC Z-boson transverse momentum data on PDF determinations
The LHC has recently released precise measurements of the transverse momentum distribution of the Z-boson that provide a unique constraint on the structure of the proton. Theoretical developments now allow the prediction of these observables through next-to-next-to-leading order (NNLO) in perturbative QCD. In this work we study the impact of incorporating these latest advances into a determination of parton distribution functions (PDFs) through NNLO including the recent ATLAS and CMS 7 TeV and 8 TeV pTZ data. We investigate the consistency of these measurements in a global fit to the available data and quantify the impact of including the pTZ distributions on the PDFs. The inclusion of these new data sets significantly reduces the uncertainties on select parton distributions and the corresponding parton-parton luminosities. In particular, we find that the pTZ data ultimately leads to a reduction of the PDF uncertainty on the gluon-fusion and vector-boson fusion Higgs production cross sections by about 30%, while keeping the central values nearly unchanged.This research was supported in part by the National Science Foundation under Grant No. NSF PHY11-25915 to the Kavli Institute of Theoretical Physics in Santa Barbara. R. B. is supported by the DOE contract DE-AC02-06CH11357. F. P. is supported by the DOE grants DE-FG02- 91ER40684 and DE-AC02-06CH11357. M. U. is supported by a Royal Society Dorothy Hodgkin Research Fellowship and partially supported by the STFC grant ST/L000385/1. A. G. is supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Sk lodowska-Curie grant agreement No 659128 - NEXTGENPDF. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357
QCD Corrections to the Radiative Decay B -> X_s gamma
In this short review, the calculation of the next-to-next-to-leading order
QCD corrections to the inclusive radiative decay B -> X_s gamma is described. I
summarize the salient features of the calculational framework adopted, discuss
the results obtained in the last few years, and indicate the technical tools
that made the NNLO calculations possible. I conclude by comparing the current
NNLO theoretical estimate for the branching ratio with the experimental
measurement and by briefly discussing the size and origin of the residual
theoretical uncertainty.Comment: 18 pages, 7 figures. Invited review for Modern Physics Letters
Quark masses in QCD: a progress report
Recent progress on QCD sum rule determinations of the light and heavy quark
masses is reported. In the light quark sector a major breakthrough has been
made recently in connection with the historical systematic uncertainties due to
a lack of experimental information on the pseudoscalar resonance spectral
functions. It is now possible to suppress this contribution to the 1% level by
using suitable integration kernels in Finite Energy QCD sum rules. This allows
to determine the up-, down-, and strange-quark masses with an unprecedented
precision of some 8-10%. Further reduction of this uncertainty will be possible
with improved accuracy in the strong coupling, now the main source of error. In
the heavy quark sector, the availability of experimental data in the vector
channel, and the use of suitable multipurpose integration kernels allows to
increase the accuracy of the charm- and bottom-quarks masses to the 1% level.Comment: Invited review paper to be published in Modern Physics Letters
Three-loop electroweak corrections to the W-boson mass and sin^2 theta_eff in the large Higgs mass limit
We present an analytical calculation of the leading three-loop radiative
correction to the S-parameter in the Standard Model in the large Higgs mass
limit. Numerically, S^(3) = 1.1105*g^4/(1024 pi^3)*m_H^4/M_W^4. When combined
with the corresponding three-loop correction to the rho-parameter, this leads
to shifts of Delta^(3) sin^2 theta_eff = 4.6*10^-9*m_H^4/M_W^4 in the effective
weak mixing angle and Delta^(3) M_W = -6.3*10^-4*MeV*m_H^4/M_W^4 in the W boson
mass. For both of these observables, the sign of the three-loop correction is
equal to that of the one-loop correction.Comment: 12 pages, two Figure
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