85,065 research outputs found
Singlet Model Interference Effects with High Scale UV Physics
One of the simplest extensions of the Standard Model (SM) is the addition of
a scalar gauge singlet, S. If S is not forbidden by a symmetry from mixing with
the Standard Model Higgs boson, the mixing will generate non-SM rates for Higgs
production and decays. In general, there could also be unknown high energy
physics that generates additional effective low energy interactions. We show
that interference effects between the scalar resonance of the singlet model and
the effective field theory (EFT) operators can have significant effects in the
Higgs sector. We examine a non- symmetric scalar singlet model and
demonstrate that a fit to the 125 GeV Higgs boson couplings and to limits on
high mass resonances, S, exhibit an interesting structure and possible large
cancellations of effects between the resonance contribution and the new EFT
interactions, that invalidate conclusions based on the renormalizable singlet
model alone.Comment: 18 pages, 7 figures; revised to emphasize the points of general
interest for heavy resonance searches at the LH
Proton exchange membrane electrolysis sustained by water vapor
The current–voltage characteristics of a proton exchange membrane (PEM) electrolyzer constructed with an IrRuOx water oxidation catalyst and a Pt black water reduction catalyst, under operation with water vapor from a humidified carrier gas, have been investigated as a function of the gas flow rate, the relative humidity, and the presence of oxygen. The performance of the system with water vapor was also compared to the performance when the device was immersed in liquid water. With a humidified Ar(g) input stream at 20 °C, an electrolysis current density of 10 mA cm^(−2) was sustained at an applied voltage of ~ 1.6 V, with a current density of 20 mA cm^(−2) observed at ~ 1.7 V. In the system evaluated, at current densities >40 mA cm^(−2) the electrolysis of water vapor was limited by the mass flux of water to the PEM. At <40 mA cm^(−2), the electrolysis of water vapor supported a given current density at a lower applied bias than did the electrolysis of liquid water. The relative humidity of the input carrier gas strongly affected the current–voltage behavior, with lower electrolysis current density attributed to dehydration of the PEM at reduced humidity values. The results provide a proof-of-concept that, with sufficiently active catalysts, an efficient solar photoelectrolyzer could be operated only with water vapor as the feedstock, even at the low operating temperatures that may result in the absence of active heating. This approach therefore offers a route to avoid the light attenuation and mass transport limitations that are associated with bubble formation in these systems
Scanning tunneling microscopy studies of monolayer templates: alkylthioethers and alkylethers
Scanning tunneling microscopy has been used to determine the molecular ordering in stable, ordered monolayers formed from long-chain normal and substituted alkanes in solution on highly oriented pyrolytic graphite surfaces. Monolayers were initially formed using an overlying solution of either a symmetrical dialkylthioether or a symmetrical dialkylether. Initially pure thioether solutions were then changed to nearly pure solutions of the identical chain-length ether, and vice versa. The direct application of a pure solution of long-chain symmetrical ethers onto graphite produced a lamellate monolayer within which the individual molecular axes were oriented at an angle of ~65° to the lamellar axes. In contrast, a pure solution of long-chain symmetrical thioethers on graphite produced a monolayer within which the molecular axes were oriented perpendicular to the lamellar axes. When ethers were gradually added to solutions overlying pure thioether monolayers, the ethers substituted into the existing monolayer structure. Thus, the ether molecules could be forced to orient in the perpendicular thioether-like manner through the use of a thioether template monolayer. Continued addition of ethers to the solution ultimately produced a nearly pure ether monolayer that retained the orientation of the thioether monolayer template. However, a monolayer of thioether molecules formed by gradual substitution into an ether monolayer did not retain the 65° orientation typical of dialkylethers, but exhibited the 90° orientation typical of dialkylthioether monolayers. The thioethers and ethers were easily distinguished in images of mixed monolayers, allowing both an analysis of the distribution of the molecules within the mixed monolayers and a comparison of the monolayer compositions with those of the overlying solutions. Substitution of molecules into the template monolayer did not proceed randomly; instead, a molecule within a monolayer was more likely to be replaced by a molecule in the overlying solution if it was located next to a molecule that had already been replaced
Threshold Resummed and Approximate NNLO results for W+W- Pair Production at the LHC
The next-to-leading order (NLO) QCD radiative corrections to W+W- production
at hadron colliders are well understood. We combine NLO perturbative QCD
calculations with soft-gluon resummation of threshold logarithms to find a
next-to-next-to leading logarithmic (NNLL) prediction for the total cross
section and the invariant mass distribution at the LHC. We also obtain
approximate next-to-next-to-leading order (NNLO) results for the total W+W-
cross section at the LHC which includes all contributions from the scale
dependent leading singular terms. Our result for the approximate NNLO total
cross section is the most precise theoretical prediction available.
Uncertainties due to scale variation are shown to be small when the threshold
logarithms are included. NNLL threshold resummation increases the W+W-
invariant mass distribution by ~ 3-4% in the peak region for both \sqrt{S}=8
and 14 TeV. The NNLL threshold resummed and approximate NNLO cross sections
increase the NLO cross section by 0.5-3% for \sqrt{S}=7, 8, 13, and 14 TeV.Comment: 29 pages, 7 figures, 3 tables. Discussion added to introduction,
references updated, and typos correcte
Solar energy conversion
If solar energy is to become a practical alternative to fossil fuels, we must have efficient ways to convert photons into electricity, fuel, and heat. The need for better conversion technologies is a driving force behind many recent developments in biology, materials, and especially nanoscience
Exploring Resonant di-Higgs production in the Higgs Singlet Model
We study the enhancement of the di-Higgs production cross section resulting
from the resonant decay of a heavy Higgs boson at hadron colliders in a model
with a Higgs singlet. This enhancement of the double Higgs production rate is
crucial in understanding the structure of the scalar potential and we determine
the maximum allowed enhancement such that the electroweak minimum is a global
minimum. The di-Higgs production enhancement can be as large as a factor of ~
18 (13) for the mass of the heavy Higgs around 270 (420) GeV relative to the
Standard Model rate at 14 TeV for parameters corresponding to a global
electroweak minimum.Comment: 25 pages, 14 figures. Version approved for publication. Discussion of
Z2 symmetric limit improved and references adde
Top Partners and Higgs Boson Production
The Higgs boson is produced at the LHC through gluon fusion at roughly the
Standard Model rate. New colored fermions, which can contribute to
, must have vector-like interactions in order not to be in
conflict with the experimentally measured rate. We examine the size of the
corrections to single and double Higgs production from heavy vector-like
fermions in singlets and doublets and search for regions of parameter
space where double Higgs production is enhanced relative to the Standard Model
prediction. We compare production rates and distributions for double Higgs
production from gluon fusion using an exact calculation, the low energy theorem
(LET), where the top quark and the heavy vector-like fermions are taken to be
infinitely massive, and an effective theory (EFT) where top mass effects are
included exactly and the effects of the heavy fermions are included to . Unlike the LET, the EFT gives an extremely accurate description
of the kinematic distributions for double Higgs production.Comment: 37 pages, 11 figures. Minor changes to Figs. 8-1
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