174 research outputs found
Slepton pair production in the POWHEG BOX
We present an implementation for slepton pair production at hadron colliders
in the POWHEG BOX, a framework for combining next-to-leading order QCD
calculations with parton-shower Monte-Carlo programs. Our code provides a SUSY
Les Houches Accord interface for setting the supersymmetric input parameters.
Decays of the sleptons and parton-shower effects are simulated with PYTHIA.
Focussing on a representative point in the supersymmetric parameter space we
show results for kinematic distributions that can be observed experimentally.
While next-to-leading order QCD corrections are sizable for all distributions,
the parton shower affects the color-neutral particles only marginally.
Pronounced parton-shower effects are found for jet distributions.Comment: 10 pages, 4 figure
Deviation from Tri-Bimaximal Mixing and Large Reactor Mixing Angle
Recent observations for a non-zero have come from various
experiments. We study a model of lepton mixing with a 2-3 flavor symmetry to
accommodate the sizable measurement. In this work, we derive
deviations from the tri-bimaximal (TBM) pattern arising from breaking the
flavor symmetry in the neutrino sector, while the charged leptons contribution
has been discussed in a previous work. Contributions from both sectors towards
accommodating the non-zero measurement are presented.Comment: 25 pages, 12 figures. arXiv admin note: text overlap with
arXiv:1109.232
Global parameterization and validation of a two-leaf light use efficiency model for predicting gross primary production across FLUXNET sites:TL-LUE Parameterization and Validation
Light use efficiency (LUE) models are widely used to simulate gross primary production (GPP). However, the treatment of the plant canopy as a big leaf by these models can introduce large uncertainties in simulated GPP. Recently, a two-leaf light use efficiency (TL-LUE) model was developed to simulate GPP separately for sunlit and shaded leaves and has been shown to outperform the big-leaf MOD17 model at six FLUX sites in China. In this study we investigated the performance of the TL-LUE model for a wider range of biomes. For this we optimized the parameters and tested the TL-LUE model using data from 98 FLUXNET sites which are distributed across the globe. The results showed that the TL-LUE model performed in general better than the MOD17 model in simulating 8 day GPP. Optimized maximum light use efficiency of shaded leaves (εmsh) was 2.63 to 4.59 times that of sunlit leaves (εmsu). Generally, the relationships of εmsh and εmsu with εmax were well described by linear equations, indicating the existence of general patterns across biomes. GPP simulated by the TL-LUE model was much less sensitive to biases in the photosynthetically active radiation (PAR) input than the MOD17 model. The results of this study suggest that the proposed TL-LUE model has the potential for simulating regional and global GPP of terrestrial ecosystems, and it is more robust with regard to usual biases in input data than existing approaches which neglect the bimodal within-canopy distribution of PAR
The Social Higgs
Using published Higgs search data we investigate whether any evidence
supports the possibility that the Higgs may be mixed with other neutral
scalars. We combine the positive evidence for the Higgs at 125.5 GeV with
search constraints at other masses to explore the viability of two simple
models. The first Higgs 'friend' model is simply a neutral scalar mixed with
the Higgs. In the second Higgs 'accomplice' model the new scalar has an
enhanced coupling to photons due to couplings to additional charged fields. We
find that the latter scenario allows improvement in fitting the data by
accommodating enhanced diphoton rates and suppression in other channels for a
Higgs mass of 125.5 GeV. Small excesses at other masses allow the additional
scalar to further improve the fit to the data, particularly if it has mass in
the vicinity of 210 GeV. Due to observed event rates at 125.5 GeV and strong
limits in high mass Higgs searches, mixing angles greater than pi/4 are
typically disfavored at the 95% confidence level, depending on the mass of the
scalar.Comment: 11 pages, 4 figures. v2 references added, Higgs data update
Aircraft Regional-Scale Flux Measurements over Complex Landscapes of Mangroves, Desert, and Marine Ecosystems of Magdalena Bay, Mexico
Natural ecosystems are rarely structurally simple or functionally homogeneous. This is true for the complex coastal region of Magdalena Bay, Baja California Sur, Mexico, where the spatial variability in ecosystem fluxes from the Pacific coastal ocean, eutrophic lagoon, mangroves, and desert were studied. The Sky Arrow 650TCN environmental research aircraft proved to be an effective tool in characterizing land–atmosphere fluxes of energy, CO2, and water vapor across a heterogeneous landscape at the scale of 1 km. The aircraft was capable of discriminating fluxes from all ecosystem types, as well as between nearshore and coastal areas a few kilometers distant. Aircraft-derived average midday CO2 fluxes from the desert showed a slight uptake of −1.32 μmol CO2 m−2 s−1, the coastal ocean also showed an uptake of −3.48 μmol CO2 m−2 s−1, and the lagoon mangroves showed the highest uptake of −8.11 μmol CO2 m−2 s−1. Additional simultaneous measurements of the normalized difference vegetation index (NDVI) allowed simple linear modeling of CO2 flux as a function of NDVI for the mangroves of the Magdalena Bay region. Aircraft approaches can, therefore, be instrumental in determining regional CO2 fluxes and can be pivotal in calculating and verifying ecosystem carbon sequestration regionally when coupled with satellite-derived products and ecosystem models
Constraining Nonstandard Neutrino-Electron Interactions due to a New Light Spin-1 Boson
We consider nonstandard interactions of neutrinos with electrons arising from
a new light spin-1 particle with mass of tens of GeV or lower and couplings to
the neutrinos and electron. This boson is not necessarily a gauge boson and is
assumed to have no mixing with standard-model gauge bosons. Adopting a
model-independent approach, we study constraints on the flavor-conserving and
-violating couplings of the boson with the leptons from a number of
experimental data. Specifically, we take into account the
(anti)neutrino-electron scattering and e^+ e^- -> nu nubar gamma measurements
and keep explicitly the dependence on the new particle mass in all
calculations. We find that one of the two sets of data can provide the stronger
constraints, depending on the mass and width of the boson. Also, we evaluate
complementary constraints on its separate flavor-conserving couplings to the
electron and neutrinos from other latest experimental results.Comment: 24 pages, 8 figures, expanded including supplementary experimental
constraints, references added, matches journal versio
Author Correction: The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data
The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data
The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.Peer reviewe
Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector
A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements
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