1,799 research outputs found
Modelling strong interactions and longitudinally polarized vector boson scattering
We study scattering of the electroweak gauge bosons in 5D warped models.
Within two different models we determine the precise manner in which the Higgs
boson and the vector resonances ensure the unitarity of longitudinal vector
boson scattering. We identify three separate scales that determine the dynamics
of the scattering process in all cases. For a quite general background geometry
of 5D, these scales can be linked to a simple functional of the warp factor.
The models smoothly interpolate between a `composite' Higgs limit and a
Higgsless limit. By holographic arguments, these models provide an effective
description of vector boson scattering in 4D models with a strongly coupled
electroweak breaking sector.Comment: 30 pages, no figure
FIRe glider: Mapping in situ chlorophyll variable fluorescence with autonomous underwater gliders
Nutrient and light availability regulate phytoplankton physiology and photosynthesis in the ocean. These physiological processes are difficult to sample in time and space over physiologically and ecologically relevant scales using traditional shipboard techniques. Gliders are changing the nature of data collection, by allowing a sustained presence at sea over regional scales, collecting data at resolution not possible using traditional techniques. The integration of a fluorescence induction and relaxation (FIRe) sensor in a Slocum glider allows autonomous high‐resolution and vertically‐resolved measurements of photosynthetic physiological variables together with oceanographic data. In situ measurements of variable fluorescence under ambient light allows a better understanding of the physical controls of primary production (PP). We demonstrate this capability in a laboratory setting and with several glider deployments in the Southern Ocean. Development of these approaches will allow for the in situ evaluation of phytoplankton light stress and photoacclimation mechanisms, as well as the role of vertical mixing in phytoplankton dynamics and the underlying physiology, especially in remote locations and for prolonged duration
CP violation in 2HDM and EFT: the ZZZ vertex
We study the CP violating ZZZ vertex in the two-Higgs doublet model, which is
a probe of a Jarlskog-type invariant in the extended Higgs sector. The form
factor is evaluated at one loop in a general gauge and its
magnitude is estimated in the realistic parameter space. Then we turn to the
decoupling limit of the two-Higgs doublet model, where the extra scalars are
heavy and the physics can be described by the Standard Model supplemented by
higher-dimensional operators. The leading operator contributing to at
one loop is identified. The CP violating ZZZ vertex is not generated in the
effective theory by dimension-8 operators, but instead arises only at the
dimension-12 level, which implies an additional suppression by powers of the
heavy Higgs mass scale.Comment: 21 pages; v2: added references and comments, appendix A on method of
regions, and appendix B on derivation of CP-violating effective Lagrangian.
Corrected discussion of dimension-12 operators contributing to ZZZ vertex.
Final JHEP versio
Volunteer Programming Impact on Urban Nebraska Nursing Home Quality of Care
CPACS Urban Research Awards
Part of the mission of the College of Public Affairs and Community Service (CPACS) is to conduct research, especially as it relates to concerns of our local and statewide constituencies. CPACS has always had an urban mission, and one way that mission is served is to preform applied research relevant to urban society in general, and the Omaha metropolitan area and other Nebraska urban communities in particular. Beginning in 2014, the CPACS Dean provided funding for the projects with high relevance to current urban issues, with the potential to apply the findings to practice in Nebraska, Iowa, and beyond
Holography, Pade Approximants and Deconstruction
We investigate the relation between holographic calculations in 5D and the
Migdal approach to correlation functions in large N theories. The latter
employs Pade approximation to extrapolate short distance correlation functions
to large distances. We make the Migdal/5D relation more precise by quantifying
the correspondence between Pade approximation and the background and boundary
conditions in 5D. We also establish a connection between the Migdal approach
and the models of deconstructed dimensions.Comment: 28 page
Supersymmetric branes with (almost) arbitrary tensions
We present a supersymmetric version of the two-brane Randall-Sundrum
scenario, with arbitrary brane tensions T_1 and T_2, subject to the bound
|T_{1,2}| \leq \sqrt{-6\Lambda_5}, where \Lambda_5 < 0 is the bulk cosmological
constant. Dimensional reduction gives N=1, D=4 supergravity, with cosmological
constant \Lambda_4 in the range \half\Lambda_5 \leq \Lambda_4 \leq 0. The case
with \Lambda_4 = 0 requires T_1 = -T_2 = \sqrt{-6\Lambda_5}. This work unifies
and generalizes previous approaches to the supersymmetric Randall-Sundrum
scenario. It also shows that the Randall-Sundrum fine-tuning is not a
consequence of supersymmetry.Comment: 19pp; Published versio
Inhibition of nitrogenase by oxygen in marine cyanobacteria controls the global nitrogen and oxygen cycles
International audienceCyanobacterial N2-fixation supplies the vast majority of biologically accessible inorganic nitrogen to nutrient-poor aquatic ecosystems. The process, catalyzed by the heterodimeric protein complex, nitrogenase, is thought to predate that of oxygenic photosynthesis. Remarkably, while the enzyme plays such a critical role in Earth's biogeochemical cycles, the activity of nitrogenase in cyanobacteria is markedly inhibited in vivo at a post-translational level by the concentration of O2 in the contemporary atmosphere leading to metabolic and biogeochemical inefficiency in N2 fixation. We illustrate this crippling effect with data from Trichodesmium spp. an important contributor of "new nitrogen" to the world's subtropical and tropical oceans. The enzymatic inefficiency of nitrogenase imposes a major elemental taxation on diazotrophic cyanobacteria both in the costs of protein synthesis and for scarce trace elements, such as iron. This restriction has, in turn, led to a global limitation of fixed nitrogen in the contemporary oceans and provides a strong biological control on the upper bound of oxygen concentration in Earth's atmosphere
Multi-nutrient, multi-group model of present and future oceanic phytoplankton communities
International audiencePhytoplankton community composition profoundly affects patterns of nutrient cycling and the dynamics of marine food webs; therefore predicting present and future phytoplankton community structure is crucial to understand how ocean ecosystems respond to physical forcing and nutrient limitations. We develop a mechanistic model of phytoplankton communities that includes multiple taxonomic groups (diatoms, coccolithophores and prasinophytes), nutrients (nitrate, ammonium, phosphate, silicate and iron), light, and a generalist zooplankton grazer. Each taxonomic group was parameterized based on an extensive literature survey. We test the model at two contrasting sites in the modern ocean, the North Atlantic (North Atlantic Bloom Experiment, NABE) and subarctic North Pacific (ocean station Papa, OSP). The model successfully predicts general patterns of community composition and succession at both sites: In the North Atlantic, the model predicts a spring diatom bloom, followed by coccolithophore and prasinophyte blooms later in the season. In the North Pacific, the model reproduces the low chlorophyll community dominated by prasinophytes and coccolithophores, with low total biomass variability and high nutrient concentrations throughout the year. Sensitivity analysis revealed that the identity of the most sensitive parameters and the range of acceptable parameters differed between the two sites. We then use the model to predict community reorganization under different global change scenarios: a later onset and extended duration of stratification, with shallower mixed layer depths due to increased greenhouse gas concentrations; increase in deep water nitrogen; decrease in deep water phosphorus and increase or decrease in iron concentration. To estimate uncertainty in our predictions, we used a Monte Carlo sampling of the parameter space where future scenarios were run using parameter combinations that produced acceptable modern day outcomes and the robustness of the predictions was determined. Change in the onset and duration of stratification altered the timing and the magnitude of the spring diatom bloom in the North Atlantic and increased total phytoplankton and zooplankton biomass in the North Pacific. Changes in nutrient concentrations in some cases changed dominance patterns of major groups, as well as total chlorophyll and zooplankton biomass. Based on these scenarios, our model suggests that global environmental change will inevitably alter phytoplankton community structure and potentially impact global biogeochemical cycles
Two loop effective kaehler potential of (non-)renormalizable supersymmetric models
We perform a supergraph computation of the effective Kaehler potential at one
and two loops for general four dimensional N=1 supersymmetric theories
described by arbitrary Kaehler potential, superpotential and gauge kinetic
function. We only insist on gauge invariance of the Kaehler potential and the
superpotential as we heavily rely on its consequences in the quantum theory.
However, we do not require gauge invariance for the gauge kinetic functions, so
that our results can also be applied to anomalous theories that involve the
Green-Schwarz mechanism. We illustrate our two loop results by considering a
few simple models: the (non-)renormalizable Wess-Zumino model and Super Quantum
Electrodynamics.Comment: 1+26 pages, LaTeX, 6 figures; a missing diagram added and typos
correcte
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