196,270 research outputs found
Detecting the Higgs boson(s) in
No full textWe consider recent experimental limits on the scalar bosons in the λSUSY framework, in which the masses of the scalar particles are increased already at tree level via a largish supersymmetric coupling between the usual Higgs doublets and a singlet. We analyze in particular the two lightest scalars, discussing the regions of parameter space excluded by LHC data
Catchment travel time distributions and water flow in soils
No full textMany details about the flow of water in soils in a hillslope are unknowable given current technologies. One way of learning about the bulk effects of water velocity distributions on hillslopes is through the use of tracers. However, this paper will demonstrate that the interpretation of tracer information needs to become more sophisticated. The paper reviews, and complements with mathematical arguments and specific examples, theory and practice of the distribution(s) of the times water particles injected through rainfall spend traveling through a catchment up to a control section (i.e., “catchment” travel times). The relevance of the work is perceived to lie in the importance of the characterization of travel time distributions as fundamental descriptors of catchment water storage, flow pathway heterogeneity, sources of water in a catchment, and the chemistry of water flows through the control section. The paper aims to correct some common misconceptions used in analyses of travel time distributions. In particular, it stresses the conceptual and practical differences between the travel time distribution conditional on a given injection time (needed for rainfall‐runoff transformations) and that conditional on a given sampling time at the outlet (as provided by isotopic dating techniques or tracer measurements), jointly with the differences of both with the residence time distributions of water particles in storage within the catchment at any time. These differences are defined precisely here, either through the results of different models or theoretically by using an extension of a classic theorem of dynamic controls. Specifically, we address different model results to highlight the features of travel times seen from different assumptions, in this case, exact solutions to a lumped model and numerical solutions of the 3‐D flow and transport equations in variably saturated, physically heterogeneous catchment domains. Our results stress the individual characters of the relevant distributions and their general nonstationarity yielding their legitimate interchange only in very particular conditions rarely achieved in the field. We also briefly discuss the impact of oversimple assumptions commonly used in analyses of tracer data
On the probability of extinction of the Haiti cholera epidemic
No full textMore than three years after its appearance in Haiti, cholera has already caused more than 8,500 deaths and 695,000 infections and it is feared to become endemic. However, no clear evidence of a stable environmental reservoir of pathogenic Vibrio cholerae, the infective agent of the disease, has emerged so far, suggesting the possibility that the transmission cycle of the disease is being maintained by bacteria freshly shed by infected individuals. Should this be the case, cholera could in principle be eradicated from Haiti. Here, we develop a framework for the estimation of the probability of extinction of the epidemic based on current information on epidemiological dynamics and health-care practice. Cholera spreading is modeled by an individual-based spatially-explicit stochastic model that accounts for the dynamics of susceptible, infected and recovered individuals hosted in different local communities connected through hydrologic and human mobility networks. Our results indicate that the probability that the epidemic goes extinct before the end of 2016 is of the order of 1 %. This low probability of extinction highlights the need for more targeted and effective interventions to possibly stop cholera in Haiti. © 2014 The Author(s)
Gravitational tests of electroweak relaxation
No full textAbstract We consider a scenario in which the electroweak scale is stabilized via the relaxion mechanism during inflation, focussing on the case in which the back-reaction potential is generated by the confinement of new strongly interacting vector-like fermions. If the reheating temperature is sufficiently high to cause the deconfinement of the new strong interactions, the back-reaction barrier then disappears and the Universe undergoes a second relaxation phase. This phase stops when the temperature drops sufficiently for the back-reaction to form again. We identify the regions of parameter space in which the second relaxation phase does not spoil the successful stabilization of the electroweak scale. In addition, the generation of the back-reaction potential that ends the second relaxation phase can be associated to a strong first order phase transition. We then study when such transition can generate a gravitational wave signal in the range of detectability of future interferometer experiments
Diphoton excess in the 2HDM: Hastening towards instability and the nonperturbative regime
No full textALPs, the on-shell way
No full textWe study how the coupling between axion-like particles (ALPs) and matter can be obtained at the level of on-shell scattering amplitudes. We identify three conditions that allow us to compute amplitudes that correspond to shift-symmetric Lagrangians, at the level of operators with dimension 5 or higher, and we discuss how they relate and extend the Adler’s zero condition. These conditions are necessary to reduce the number of coefficients consistent with the little-group scaling to the one expected from the Lagrangian approach. We also show how our formalism easily explains that the dimension-5 interaction involving one ALP and two massless spin-1 bosons receive corrections from higher order operators only when the ALP has a non-vanishing mass. As a direct application of our results, we perform a phenomenological study of the inelastic scattering l+l− → φh (with l± two charged leptons, φ the ALP and h the Higgs boson) for which, as a result of the structure of the 3-point and 4-point amplitudes, dimension-7 operators can dominate over the dimension-5 ones well before the energy reaches the cutoff of the theory
A Minimalist Model of Salt-Marsh Vegetation Dynamics Driven by Species Competition and Dispersal
No full textWe present a new bidimensional, spatially-explicit ecological model describing the dynamics of halophytic vegetation in tidal saline wetlands. Existing vegetation models employ relatively simple deterministic or stochastic mechanisms, and are driven by local environmental conditions. In the proposed model, in contrast, vegetation dynamics depend not only on the marsh local habitat, but also on spatially-explicit mechanisms of dispersal and competition among multiple interacting species. The role of habitat quality, here determined by the local elevation relative to the mean sea level as a proxy for environmental conditions, is mathematically modeled by a logistic function that represents the fundamental (theoretical) niche of each halophytic species. Hence, the model does not artificially impose any constraints to the ability of a species to colonize elevated areas where it is usually not observed: such limitations naturally arise through competition with fitter species across marsh topographic gradients. We qualitatively test our model against field data based on a suitable assemblage of focus species, and perform a sensitivity analysis aimed at determining how dynamic equilibria in vegetation distributions are affected by changes in model input parameters. Results indicate that the model is robust and can predict realistic vegetation distributions and species-richness patterns. More importantly, the model is also able to effectively reproduce the outcomes of classical ecological experiments, wherein a species is transplanted to an area outside its realized niche. A direct comparison shows that previous models not accounting for dispersal and interspecific competitions are unable to reproduce such dynamics. Our model can be easily integrated into virtually any existing morphodynamic model, thereby strengthening our ability to simulate the coupled biotic and abiotic evolution of salt marshes under changing climate forcings
How network structure can affect nitrogen removal by streams
No full textStreams and rivers can be highly reactive sites for nitrogen (N) transformation and removal. Empirical and model-based research show how location in a stream network affects rates of N removal. Because the structure of stream networks can vary widely and N cycling in headwater streams may affect N cycling in downstream reaches, we hypothesised that network structure may affect whole stream network processing of N. We generated three stream networks with the same catchment area but differing shapes, based on optimal channel network theory. We applied a model of nitrate (NO3-) transport and denitrification, and implemented model scenarios to examine how network shape affects NO3- removal with (1) increased NO3- loading from the catchment, (2) altered spatial distributions of NO3- loading and (3) decreased drainage density (i.e. loss of headwater streams). For all stream networks, the fraction of total NO3- removed decreased with increasing NO3- loading from the catchment. Stream networks in narrow catchments removed a higher fraction of NO3-, particularly at intermediate NO3- loading rates. Network shape also controlled the distribution of removal in small versus large streams, with larger streams removing a higher fraction of the total NO3- load in narrower networks. The effects of network shape on NO3- removal when the spatial distribution of NO3- loading was altered varied with the magnitude of NO3- loading. At low loads, NO3- was entirely removed when added to distal parts of the stream network, and about 50% removed when added near the outlet; there was no effect of network shape. At intermediate and high loads, the fraction of total NO3- load removed by the narrow stream network was 1.5Ã\u97 higher than the rectangular and square networks when NO3- was added to distal parts of the networks. Network shape did not have an effect when NO3- load occurred near the outlet, regardless of the magnitude of the NO3- load. The fraction of total NO3- removed by the stream network was up to 5% lower when drainage density was reduced from 1.0 to 0.74 km-1, with the least change for the narrow network. Reducing the drainage density also altered the role of small relative to large streams, with the net effect of moving the location of NO3- removal downstream. Overall, effects of network shape contributed up to 20% of the variation in the fraction of NO3- removed by stream networks. Network shape was most important at intermediate to high NO3- loads and when NO3- was loaded to distal parts of the catchment. The narrow network removed more NO3- across model scenarios, with elevated removal in larger streams explaining most of the difference. We suggest the shape of the catchment may modulate the degree to which large streams contribute to whole network NO3- removal
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