346 research outputs found
Top quark associated production of the neutral top-pion at high energy colliders
In the context of topcolor-assisted technicolor (TC2) models, we calculate
the associated production of the neutral top-pion with a pair of
top quarks via the process . We
find that the production cross section is larger than that of the process both in the standard model (SM) and in the
minimal supersymmetric SM. With reasonable values of the parameters in TC2
models, the cross section can reach . The neutral top-pion
may be direct observed via this process.Comment: Latex files, 10 pages and 3 figure
Hadron Collider Signatures for New Interactions of Top and Bottom Quarks
One of the main goals for hadron colliders is the study of the properties of
the third generation quarks. We study the signatures for new TeV resonances
that couple to top or bottom quarks both at the Tevatron Run II and at the LHC.
We find that in the simplest production processes of Drell-Yan type at the
Tevatron, the signals are overwhelmed by QCD backgrounds. We also find that it
is possible to study these resonances when they are produced in association
with a pair of heavy quarks or in association with a single top at the LHC.In
particular, with an integrated luminosity of 300 fb at the LHC, it is
possible to probe resonance masses up to around 2 TeV.Comment: 24 pages, 15 figures, Minor corrections, version to appear in Phys.
Rev.
Detecting the neutral top-pion at colliders
We investigate some processes of the associated production of a neutral
top-pion with a pair of fermions() in the context of top-color-assisted technicolor(TC2)
theory at future colliders.
The studies show that the largest cross sections of the processes
could only reach the
level of 0.01fb, we can hardly detect a neutral top-pion through these
processes. For the processes ,
and ,
the cross sections of these processes are at the level of a few fb for the
favorable parameters and a few tens, even hundreds, of neutral top-pion events
can be produced at future colliders each year through these
processes. With the clean background of the flavor-changing channel,
the top-pion events can possibly be detected at the planned high luminosity
colliders. Therefore, such neutral top-pion production processes
provide a useful way to detect a neutral top-pion and test the TC2 model
directly.Comment: 13 pages, 4 figure
Construction of markov processes from hitting distributions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47648/1/440_2004_Article_BF00538487.pd
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
in NonCommutative Standard Model
We study the top quark decay to b quark and W boson in the NonCommutative
Standard Model (NCSM). The lowest contribution to the decay comes from the
terms quadratic in the matrix describing the noncommutative (NC) effects while
the linear term is seen to identically vanish because of symmetry. The NC
effects are found to be significant only for low values of the NC
characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More
discussion included. To appear in PR
Single Top Production as a Window to Physics Beyond the Standard Model
Production of single top quarks at a high energy hadron collider is studied
as a means to identify physics beyond the standard model related to the
electroweak symmetry breaking. The sensitivity of the -channel mode,
the -channel -gluon fusion mode, and the \tw mode to various possible
forms of new physics is assessed, and it is found that the three modes are
sensitive to different forms of new physics, indicating that they provide
complimentary information about the properties of the top quark. Polarization
observables are also considered, and found to provide potentially useful
information about the structure of the interactions of top.Comment: References added and minor discussion improvements; results
unchanged; Version to be published in PR
New hadrons as ultra-high energy cosmic rays
Ultra-high energy cosmic ray (UHECR) protons produced by uniformly
distributed astrophysical sources contradict the energy spectrum measured by
both the AGASA and HiRes experiments, assuming the small scale clustering of
UHECR observed by AGASA is caused by point-like sources. In that case, the
small number of sources leads to a sharp exponential cutoff at the energy
E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve
this cutoff problem. For the first time we discuss the production of such
hadrons in proton collisions with infrared/optical photons in astrophysical
sources. This production mechanism, in contrast to proton-proton collisions,
requires the acceleration of protons only to energies E<10^{21} eV. The diffuse
gamma-ray and neutrino fluxes in this model obey all existing experimental
limits. We predict large UHE neutrino fluxes well above the sensitivity of the
next generation of high-energy neutrino experiments. As an example we study
hadrons containing a light bottom squark. These models can be tested by
accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR
New lattice approaches to the rule
Lattice QCD should allow a derivation of the rule from first
principles, but numerical calculations to date have been plagued by a variety
of problems. After a brief review of these problems, we present several new
methods for calculating amplitudes. These are designed for Wilson
fermions, though they can be used also with staggered fermions. They all
involve a non-perturbative determination of matching coefficients. We show how
problems of operator mixing can be greatly reduced by using point-split
hadronic currents, and how CP violating parts of the amplitudes
can be calculated by introducing a fake top quark. Many of the methods can also
be applied to the calculation of two body non-leptonic B-meson decays.Comment: 22 pages, 1 figure, uses epsfi
Two-Loop O(alpha_s G_F M_Q^2) Heavy-Quark Corrections to the Interactions between Higgs and Intermediate Bosons
By means of a low-energy theorem, we analyze at O(alpha_s G_F M_Q^2) the
shifts in the Standard-Model W^+W^-H and ZZH couplings induced by virtual
high-mass quarks, Q, with M_Q >> M_Z, M_H, which includes the top quark.
Invoking the improved Born approximation, we then find the corresponding
corrections to various four- and five-point Higgs-boson production and decay
processes which involve the W^+W^-H and ZZH vertices with one or both of the
gauge bosons being connected to light-fermion currents, respectively. This
includes e^+e^- -> f anti-f H via Higgs-strahlung, via W^+W^- fusion (with f =
nu_e), and via ZZ fusion (with f = e), as well as H -> 2V -> 4f (with V = W,
Z).Comment: 20 pages (Latex); Physical Review D (to appear
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