304 research outputs found
Kinematical Limits on Higgs Boson Production via Gluon Fusion in Association with Jets
In this paper, we analyze the high-energy limits for Higgs boson plus two jet
production. We consider two high-energy limits, corresponding to two different
kinematic regions: a) the Higgs boson is centrally located in rapidity between
the two jets, and very far from either jet; b) the Higgs boson is close to one
jet in rapidity, and both of these are very far from the other jet. In both
cases the amplitudes factorize into impact factors or coefficient functions
connected by gluons exchanged in the t channel. Accordingly, we compute the
coefficient function for the production of a Higgs boson from two off-shell
gluons, and the impact factors for the production of a Higgs boson in
association with a gluon or a quark jet. We include the full top quark mass
dependence and compare this with the result obtained in the large top-mass
limit.Comment: 35 pages, 6 figure
Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential
We address the issue of the reconstruction of the scalar potential of a
two-Higgs doublet model having in mind that of the MSSM.
We first consider the general CP conserving dim-4 effective potential. To
fully reconstruct this potential, we show that even if all the Higgs masses and
their couplings to the standard model particles are measured one needs not only
to measure certain trilinear Higgs self-couplings but some of the quartic
couplings as well. We also advocate expressing the Higgs self couplings in the
mass basis. We show explicitly, that in the so-called decoupling limit, the
most easily accessible Higgs self-couplings are given in terms of the Higgs
mass while all other dependencies on the parameters of the general effective
potential are screened. This helps also easily explain how, in the
MSSM, the largest radiative corrections which affect these self couplings are
reabsorbed by using the corrected Higgs mass. We also extend our analysis to
higher order operators in the effective Higgs potential. While the above
screening properties do not hold, we argue that these effects must be small and
may not be measured considering the foreseen poor experimental precision in the
extraction of the SUSY Higgs self-couplings.Comment: 25 pages, 3 figure
Electromagnetic corrections in eta --> 3 pi decays
We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at
next-to-leading order in the chiral expansion, arguing that effects of order
e^2(m_u-m_d) disregarded so far are not negligible compared to other
contributions of order e^2 times a light quark mass. Despite the appearance of
the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall
corrections remain small.Comment: 21 pages, 11 figures; references updated, version published in EPJ
Precise Prediction for M_W in the MSSM
We present the currently most accurate evaluation of the W boson mass, M_W,
in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase
dependence at the one-loop level, all available MSSM two-loop corrections as
well as the full Standard Model result have been included. We analyse the
impact of the different sectors of the MSSM at the one-loop level with a
particular emphasis on the effect of the complex phases. We discuss the
prediction for M_W based on all known higher-order contributions in
representative MSSM scenarios. Furthermore we obtain an estimate of the
remaining theoretical uncertainty from unknown higher-order corrections.Comment: 38 pages, 25 figures. Minor corrections, additional reference
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
The transverse momentum distribution is computed for inclusive Higgs
boson production at the energy of the CERN Large Hadron Collider. We focus on
the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and
incorporate contributions from the quark-gluon and quark-antiquark channels.
Using an impact-parameter -space formalism, we include all-orders
resummation of large logarithms associated with emission of soft gluons. Our
resummed results merge smoothly at large with the fixed-order
expectations in perturbative quantum chromodynamics, as they should, with no
need for a matching procedure. They show a high degree of stability with
respect to variation of parameters associated with the non-perturbative input
at low . We provide distributions for Higgs boson masses
from to 200 GeV. The average transverse momentum at zero rapidity
grows approximately linearly with mass of the Higgs boson over the range ~GeV. We provide analogous results
for boson production, for which we compute GeV. The
harder transverse momentum distribution for the Higgs boson arises because
there is more soft gluon radiation in Higgs boson production than in
production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in
wording. Published in Phys. Rev. D67, 034026 (2003
Aspects of Two-Photon Physics at Linear e+e- Colliders
We discuss various reactions at future e+e- and gamma-gamma colliders
involving real (beamstrahlung or backscattered laser) or quasi--real
(bremsstrahlung) photons in the initial state and hadrons in the final state.
The production of two central jets with large pT is described in some detail;
we give distributions for the rapidity and pT of the jets as well as the
di--jet invariant mass, and discuss the relative importance of various initial
state configurations and the uncertainties in our predictions. We also present
results for `mono--jet' production where one jet goes down a beam pipe, for the
production of charm, bottom and top quarks, and for single production of W and
Z bosons. Where appropriate, the two--photon processes are compared with
annihilation reactions leading to similar final states. We also argue that the
behaviour of the total inelastic gamma-gamma cross section at high energies
will probably have little impact on the severity of background problems caused
by soft and semi--hard (`minijet') two--photon reactions. We find very large
differences in cross sections for all two--photon processes between existing
designs for future e+e- colliders, due to the different beamstrahlung spectra;
in particular, both designs with >1 events per bunch crossing exist.Comment: 51 pages, 13 figures(not included
Higgs Boson Decay into Hadronic Jets
The remarkable agreement of electroweak data with standard model (SM)
predictions motivates the study of extensions of the SM in which the Higgs
boson is light and couples in a standard way to the weak gauge bosons.
Postulated new light particles should have small couplings to the gauge bosons.
Within this context it is natural to assume that the branching fractions of the
light SM-like Higgs boson mimic those in the standard model. This assumption
may be unwarranted, however, if there are non-standard light particles coupled
weakly to the gauge bosons but strongly to the Higgs field. In particular, the
Higgs boson may effectively decay into hadronic jets, possibly without
important bottom or charm flavor content. As an example, we present a simple
extension of the SM, in which the predominant decay of the Higgs boson occurs
into a pair of light bottom squarks that, in turn, manifest themselves as
hadronic jets. Discovery of the Higgs boson remains possible at an
electron-positron linear collider, but prospects at hadron colliders are
diminished substantially.Comment: 30 pages, 7 figure
Search for the lepton flavor violating decay A^0/H^0 --> tau^{+/-} mu^{+/-} at hadron colliders
In the two Higgs doublet model type III and in several other extensions of
the Standard Model, there are no discrete symmetries that suppress flavor
changing couplings at tree level. The experimental observation of the nu_mu --
nu_tau flavor oscillation may suggest the non-conservation of lepton number.
This would lead to the decay of the type A^0/H^0 --> tau^{+/-} mu^{+/-}. We
determine the present low energy limit on lepton flavor violating (LFV)
couplings from the muon g-2 measurement and discuss the prospects for detecting
lepton flavor violating decays at the TeVatron and at the Large Hadron
Collider. The achievable bounds on the LFV coupling parameter lambda_{tau mu}
are presented.Comment: 19 pages, 21 figures. Updated version takes into account the recent
results on the muon g-2 measurements. Submitted to Phys. Rev. D. Added minor
corrections from a refere
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