70 research outputs found
Evaluation of modeled changes in extreme precipitation in Europe and the Rhine basin
In this study, we investigate the change in multi-day precipitation extremes in late winter in Europe using observations and climate models. The objectives of the analysis are to determine whether climate models can accurately reproduce observed trends and, if not, to find the causes of the difference in trends. Similarly to an earlier finding for mean precipitation trends, and despite a lower signal to noise ratio, climate models fail to reproduce the increase in extremes in much of northern Europe: the model simulations do not cover the observed trend in large parts of this area. A dipole in the sea-level pressure trend over continental Europe causes positive trends in extremes in northern Europe and negative trends in the Iberian Peninsula. Climate models have a much weaker pressure trend dipole and as a result a much weaker ( extreme) precipitation response. The inability of climate models to correctly simulate observed changes in atmospheric circulation is also primarily responsible for the underestimation of trends in the Rhine basin. When it has been adjusted for the circulation trend mismatch, the observed trend is well within the spread of the climate model simulations. Therefore, it is important that we improve our understanding of circulation changes, in particular related to the cause of the apparent mismatch between observed and modeled circulation trends over the past century
Electroweak effects in top-quark pair production at Hadron Colliders
Top-quark physics plays an important role at hadron colliders such as the
Tevatron collider at Fermilab or the upcoming Large Hadron Collider (LHC) at
CERN. Given the planned experimental precision, detailed theoretical
predictions are mandatory. In this article we present analytic results for the
complete electroweak corrections to gluon induced top-quark pair production,
completing our earlier results for the quark-induced reaction. As an
application we discuss top-quark pair production at Tevatron and at LHC. In
particular we show that, although small for inclusive quantities, weak
corrections can be sizeable for differential distribution
The MSSM prediction for W+/- H-/+ production by gluon fusion
We discuss the associated W+/- H-/+ production in p p collision for the Large
Hadron Collider. A complete one-loop calculation of the loop-induced subprocess
g g -> W+/- H-/+ is presented in the framework of the Minimal Supersymmetric
Standard Model (MSSM), and the possible enhancement of the hadronic cross
section is investigated under the constraint from the squark direct-search
results and the low-energy precision data. Because of the large destructive
interplay in the quark-loop contributions between triangle-type and box-type
diagrams, the squark-loop contributions turn out to be comparable with the
quark-loop ones. In particular, the hadronic cross section via gluon fusion can
be extensively enhanced by squark-pair threshold effects in the box-type
diagrams, so that it can be as large as the hadronic cross section via the b
b-bar -> W+/- H-/+ subprocess which appears at tree level.Comment: 35 pages, 7 figures, version to appear in Physical Review
QCD and QED Corrections to Higgs Boson Production in Charged Current Scattering
First order QCD and leading QED corrections to Higgs boson production in the
channel are calculated for the
kinematical conditions at LEP LHC (\sqrt{s} = 1360 \GeV) and the
interesting mass range 80 < M_H < 150 \GeV. In the DIS scheme the QCD
corrections (not including the corrections to the branching ratio, which are
well-known) are found to be about 1\% for the total cross section and
to for the observable cross section as defined by appropriate cuts. The
latter results depend on the definition of these cuts. The QED corrections
amount to about . Also obtainable with anonymous ftp from
gluon.hep.physik.uni-muenchen.de.Comment: latex, 16 pages + 9 pages figures in PostScript (included
Bounds on the mass of the b' quark, revisited
Recent results from the DELPHI collaboration led us to review the present
bounds on the b' quark mass. We use all available experimental data for m_b' >
96 GeV to constrain the b' quark mass as a function of the
Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We
find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX
Associated Top Quark-Higgs Boson Production at the LHC
We compute the O(alpha_s^3) inclusive cross section for the process pp ->
t-tbar-h in the Standard Model, at sqrt(s)=14 TeV. The next-to-leading order
corrections drastically reduce the renormalization and factorization scale
dependence of the Born cross section and increase the total cross section for
renormalization and factorization scales larger than m_t. These corrections
have important implications for models of new physics involving the top quark.Comment: 5 pages, 4 figures, RevTeX
CP Nonconservation in
CP violation effects in are examined. CP-odd,
-odd and -even observables can both be used to extract information on
the real and imaginary parts of Feynman amplitudes. Two Higgs doublet model
with CP violating phase from neutral Higgs exchange is used to estimate
possible effects.Comment: 9 pages, 4 Figures, Late
A FORTRAN code for in SM and MSSM
Through the present paper, the code gamgamZZ is presented, which may be used
to calculate all possible observables related to the process , in either the Standard Model (SM), or the minimal sypersymmetric standard
model (MSSM) with real parameters.Comment: 13 pages, 7 figures Revised according to the EPJC Referee suggestion
Chapter 11 - Near-term climate change: Projections and predictability
This chapter assesses the scientific literature describing expectations for near-term climate (present through mid-century). Unless otherwise stated, "near-term" change and the projected changes below are for the period 2016-2035 relative to the reference period 1986-2005. Atmospheric composition (apart from CO2; see Chapter 12) and air quality projections through to 2100 are also assessed
- …