1,721,124 research outputs found
On the MSSM with hierarchical squark masses and a heavier Higgs boson
Full text linkIn the context of supersymmetric extensions of the Standard Model, we consider a spectrum in which the lightest Higgs boson has mass between 200 and 300 GeV and the first two generations of squarks have masses above 20TeV, considering the Higgs boson mass and the Supersymmetric Flavour Problem as related naturalness problems. After the analysis of some models in which the previous spectrum can be naturally realized, we consider the phenomenological consequences for the LHC and for Dark Matter
<i>tran</i>-SAS v1.0: a numerical model to compute catchment-scale hydrologic transport using StorAge Selection functions
Full text linkThis paper presents the tran-SAS package, which
includes a set of codes to model solute transport and water residence times
through a hydrological system. The model is based on a catchment-scale
approach that aims at reproducing the integrated response of the system at
one of its outlets. The codes are implemented in MATLAB and are meant to be
easy to edit, so that users with minimal programming knowledge can adapt them
to the desired application. The problem of large-scale solute transport has
both theoretical and practical implications. On the one side, the ability to
represent the ensemble of water flow trajectories through a heterogeneous
system helps unraveling streamflow generation processes and allows us to make
inferences on plant–water interactions. On the other side, transport models
are a practical tool that can be used to estimate the persistence of solutes
in the environment. The core of the package is based on the implementation of
an age master equation (ME), which is solved using general StorAge Selection
(SAS) functions. The age ME is first converted into a set of ordinary
differential equations, each addressing the transport of an individual
precipitation input through the catchment, and then it is discretized using
an explicit numerical scheme. Results show that the implementation is
efficient and allows the model to run in short times. The numerical accuracy
is critically evaluated and it is shown to be satisfactory in most cases of
hydrologic interest. Additionally, a higher-order implementation is provided
within the package to evaluate and, if necessary, to improve the numerical
accuracy of the results. The codes can be used to model streamflow age and
solute concentration, but a number of additional outputs can be obtained by
editing the codes to further advance the ability to understand and model
catchment transport processes
A Coupled O2‐CO2 Model for Joint Estimation of Stream Metabolism, O‐C Stoichiometry, and Inorganic Carbon Fluxes
Full text linkWe determine where stream carbon dioxide (CO2) comes from by developing a model for the joint estimation of stream metabolism, oxygen-carbon (O-C) stoichiometry, and fluxes of dissolved inorganic carbon (DIC), based on observations of stream oxygen (O2) and CO2 concentrations. The model is based on a stream reach mass balance of O2, DIC, and total alkalinity, and it accounts for the carbonate system and the contribution of lateral flow. O2 and DIC mass balances are coupled through stoichiometric coefficients for photosynthesis and combined autotrophic and heterotrophic respiration. Under the assumption of constant alkalinity and circumneutral pH, the model simplifies and includes 8 parameters, which are estimated through a Bayesian hierarchical framework. The model accurately reproduced time series of O2 and Co2 from three diverse sites across size and carbonate chemistry gradients. Results allow partitioning of the stream DIC budget, and thus the source of stream CO2 outgassing, into internal (in-stream net ecosystem production) and external (lateral input of terrestrial DIC and atmospheric input) contributions. We observed that the estimated stoichiometric coefficients were typically different from 1—contrary to typical assumptions—leading to divergent estimates of stream CO2 sources depending on the measurement (i.e., O2 vs. C). Parameter posterior distributions revealed the source of parameter uncertainty and the equifinality of some processes in reproducing stream CO2 dynamics, suggesting targeted variables to further investigate in order to better constrain stream C balance. The proposed model is a useful tool for incorporating the rapidly growing stream CO2 data sets into our understanding of terrestrial-aquatic C linkages
Mapping landscape connectivity as a driver of species richness under tectonic and climatic forcing
Full text linkSpecies distribution and richness ultimately result from complex interactions between biological, physical, and environmental factors. It has been recently shown for a static natural landscape that the elevational connectivity, which measures the proximity of a site to others with similar habitats, is a key physical driver of local species richness. Here we examine changes in elevational connectivity during mountain building using a landscape evolution model. We find that under uniform tectonic and variable climatic forcing, connectivity peaks at mid-elevations when the landscape reaches its geomorphic steady state and that the orographic effect on geomorphic evolution tends to favour lower connectivity on leeward-facing catchments. Statistical comparisons between connectivity distribution and results from a metacommunity model confirm that to the 1st order, landscape elevation connectivity explains species richness in simulated mountainous regions. Our results also predict that low-connectivity areas which favour isolation, a driver for in situ speciation, are distributed across the entire elevational range for simulated orogenic cycles. Adjustments of catchment morphology after the cessation of tectonic activity should reduce speciation by decreasing the number of isolated regions
Complex dark photon dark matter EFT
Full text linkWe construct an effective field theory for complex Stueckelberg dark photon dark matter. Such an effective construction can be realized by writing down a complete set of operators up to dimension six built with the complex dark photon and Standard Model fields. Classifying the effective operators, we find that in order to properly take into account the non-renormalizable nature of an interacting massive vector, the size of the Wilson coefficients should be naturally smaller than naively expected. This can be consistently taken into account by a proper power counting, that we suggest. First we apply this to collider bounds on light dark matter, then to direct detection searches by extending the list of non-relativistic operators to include the case of complex vectors. In the former we correctly find scaling limits for small masses, while in the latter we mostly focus on electric dipole interactions, that are the signatures of this type of dark matter. Simple UV completions that effectively realize the above scenarios are also outlined
Diphoton excess in the 2HDM: Hastening towards instability and the nonperturbative regime
No full textCatchment Dissolved Organic Carbon Transport: A Modeling Approach Combining Water Travel Times and Reactivity Continuum
Full text linkQuantifying the transfer of organic carbon from the terrestrial to the riverine ecosystems is of crucial importance to fully appreciate the carbon cycle at the catchment, regional and global scales. In this study, we propose a framework for modeling the flux of dissolved organic carbon (DOC) from hillslopes to stream and river networks which couples a transport model based on travel time distributions with the reactivity continuum (RC) approach to model DOC degradation. We test the model by applying it to the Plynlimon catchments (UK) exploiting both weekly and high-frequency (7-hr interval) time-series. We use information about chloride to get an independent estimate of water travel times using the framework of StorAge Selection functions. Following the RC model, the composition and the degradation of DOC along the flowpaths, and its consequent concentration in the streamflow, is described assuming that DOC is composed by a mixture of compounds that follows a continuous spectrum of reactivity. For the high-frequency data set, the model is able to reproduce DOC streamflow concentrations and to capture the complex hysteretic relation between DOC concentration and discharge. Weekly data are instead not frequent enough to properly describe DOC dynamics in this catchment. The distribution of the age of the water comprised in the streamflow proves thus a key variable to predict the quantity and the reactivity of the DOC exported from soils, and the effect of hydrologic variability on this process
- …
