898 research outputs found
Experimental and theoretical evidence for a hydrogen stabilized c 2x2 reconstruction of the P rich InP 001 surface
The formation of hydrogen bonds was investigated on the P rich InP 001 surface employing attenuated total reflection Fourier transform infrared spectroscopy, low energy electron diffraction, and total energy density functional theory calculations. Strong evidence was found for a c 2 2 2P 3H reconstruction with a higher hydrogen coverage than is characteristic for the metal organic chemical vapor deposition prepared hydrogen stabilized 2 2 2D 2H surface. The new surface reconstruction was formed upon exposure to atomic hydrogen. Complete transformation of all the metastable atomic configurations to form the new surface reconstruction was not achieved, since prior to this the surface began to deteriorate. The latter effect was monitored as the formation of In H bonds. Two observations, i.e., nearly complete screening of the infrared peaks for excitation with p polarized light and a pronounced redshift of P H peaks with increasing hydrogen coverage were attributed to dipole dipole interaction between the vibrating adsorbate
Exact results for the reactivity of a single-file system
We derive analytical expressions for the reactivity of a Single-File System
with fast diffusion and adsorption and desorption at one end. If the conversion
reaction is fast, then the reactivity depends only very weakly on the system
size, and the conversion is about 100%. If the reaction is slow, then the
reactivity becomes proportional to the system size, the loading, and the
reaction rate constant. If the system size increases the reactivity goes to the
geometric mean of the reaction rate constant and the rate of adsorption and
desorption. For large systems the number of nonconverted particles decreases
exponentially with distance from the adsorption/desorption end.Comment: 4 pages, 2 figure
Gluino Pair Production at Linear e^+e^- Colliders
We study the potential of high-energy linear colliders for the
production of gluino pairs within the Minimal Supersymmetric Standard Model
(MSSM). In this model, the process is mediated by
quark/squark loops, dominantly of the third generation, where the mixing of
left- and right-handed states can become large. Taking into account realistic
beam polarization effects, photon and -boson exchange, and current mass
exclusion limits, we scan the MSSM parameter space for various
center-of-mass energies to determine the regions, where gluino production
should be visible.Comment: 22 pages, 9 figure
On MSSM charged Higgs boson production in association with an electroweak W boson at electron positron colliders
We present a calculation of the cross section for the process e+ e- --> W+/-
H-/+ in the minimal supersymmetric standard model (MSSM) and the Two Higgs
Doublet Model (THDM). We study the basic features of the MSSM prediction for
some distinctive parameter scenarios. We find large effects from virtual
squarks for scenarios with large mixing in the stop sector which can lead to a
cross section vastly different from a THDM with identical Higgs sector
parameters. We investigate this interesting behaviour in more detail by
thoroughly scanning the MSSM parameter space for regions of large cross
section. For a charged Higgs boson too heavy to be pair-produced at such a
machine, it turns out that a large MSSM cross section with a good chance of
observation is linked to a squark mass scale below 600 GeV and a considerable
amount of mixing in either the stop and sbottom sector.Comment: 25 pages, 10 figures (two in colour). Substantially improved on the
MSSM parameter restrictions taken into account. Added some reference
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
Electroweak Precision Observables within a Fourth Generation Model with General Flavour Structure
We calculate the contributions to electroweak precision observables (EWPOs)
due to a fourth generation of fermions with the most general (quark-)flavour
structure (but assuming Dirac neutrinos and a trivial flavour structure in the
lepton sector). The new-physics contributions to the EWPOs are calculated at
one-loop order using automated tools (FeynArts/FormCalc). No further
approximations are made in our calculation. We discuss the size of non-oblique
contributions arising from Z--quark--anti-quark vertex corrections and the
dependence of the EWPOs on all CKM mixing angles involving the fourth
generation. We find that the electroweak precision observables are sensitive to
two of the fourth-generation mixing angles and that the corresponding
constraints on these angles are competitive with those obtained from flavour
physics. For non-trivial 4x4 flavour structures, the non-oblique contributions
lead to relative corrections of several permille and should be included in a
global fit
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
Supersymmetric effects in top quark decay into polarized W-boson
We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak
(SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal
or transverse W-boson. The corrections are presented in terms of the
longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio
\Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both
SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1%
in magnitude and they tend to have opposite signs. The corrections to the total
width \Gamma(t-->W b) are also presented for comparison with the existing
results in the literature. We find that our SUSY-EW corrections to the total
width differ significantly from previous studies: the previous studies give a
large correction of more than 10% in magnitude for a large part of the
parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
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