1,721,161 research outputs found
Supersymmetric Models with a hierarchical squark spectrum and a heavy Higgs boson
No full textLow energy Supersymmetry is one of the best motivated extensions of the
Standard Model of Particle Physics. Here we focus on a particular supersymmetric
framework, taking the masses of the squarks of the rest two generations much
larger than the others and a Higgs boson mass in the (200 ÷ 300) GeV range.
The motivation is twofold: on the one hand a high mass scale for the squarks
of the rest two generations allows at least to soften the Supersymmetric Flavour
problem; on the other hand, a higher Higgs boson mass allows to explain the
lack of signals in the Higgs sector. In Chapter 1 we summarise the main features
of supersymmetric models at the Fermi scale and we identify the problems that
shall be the subject of this thesis. In Chapter 2 we will consider the "Higgs boson
mass problem" and the "Supersymmetric Flavour problem" as related naturalness
problems. In Chapter 3 some phenomenological aspects of supersymmetric
theories with such a "non standard" sparticle spectrum will be studied, namely
gluino decays, production and decay rates of the lightest Higgs boson and some
aspects relevant for the Dark Matter direct detection. At last, in Chapter 4,
we will turn our attention to
flavour signals, implementing an eff ective Minimal
Flavour Violation in the case of a hierarchical squark spectrum and deriving lower
bounds on the masses of the heavy squarks that allow to have agreement with
experiments. The overall conclusions are summarised in Chapter 5
On the scaling of river network biogeochemical function
No full textRiver networks play a fundamental biogeochemical role in the Earth system by transporting and processing materials from terrestrial to ocean ecosystems. The cumulative biogeochemical function of a watershed of area A can broadly be referred to as the total processing rate of material performed by its river network. An important recent research, conducted through network simulations, has revealed that the biogeochemical function of rivers can scale superlinearly with the area A under certain scenarios. This finding has significant implications for the role of river networks in regional and global biogeochemical cycles. Here, we demonstrate how such scaling can be derived analytically by combining the power law distribution of drainage area, the universal fractal signature of river networks and the scaling of channel hydraulic geometry, utilising the theory of finite-size scaling. The results enable the discrimination between linear and superlinear behaviours, as well as the calculation of the exact exponent based on parameters that define how the biogeochemical function and the river width change with river drainage area. Furthermore, we investigate the difference between the scaling of the biogeochemical function with the area of the watershed (Formula presented.) and with the area of a region drained by multiple river networks, emphasising the implications for upscaling efforts
River Networks as Ecological Corridors
Full text linkRiver networks and the transport processes that take place in them provide a natural integrating framework for the study of hydrologic, biologic and ecologic processes in river basins. The profound commonalities existing among all types of river basins and their drainage networks, together with the key role that hese structures play in the above dynamics, encourage the search for general behaviours. The aim of this work is to put the basis for a general framework for the analysis of complex system associated with dendritic landscapes. In particular we investigate how the environmental matrix constituted by the ecological corridors defined by the river network could affect patterns and dynamics of the system itself. We first analyze invasion, an ecological process that describe the growth and the spreading of a species in a new territory, finding that the speed
of colonization is strongly affected by the structure of the network and the bias of the transport. These hydrological controls provide a null model for the comparison with more complex ecologic processes like the spreading of waterborne diseases. We compare epidemiological data from the real world with the spacetime evolution of infected individuals predicted by a theoretical scheme based on reactive transport of infective agents through a biased network portraying actual river pathways. The scheme is remarkably capable of reproducing actual outbreaks and shows that spatial distribution of different communities and how they are interconnected trough the river network, could indeed affect epidemic dynamics. The previous models are then generalized studying river biogeography.
We analyse how the dispersion and growth of several species that compete for the same resources control river biodiversity. We propose a neutral metacommunity model that incorporates network structure. The scheme, along with a proper description
of the habitat capacity distribution, is able to simultaneously reproduce several biodiversity patterns of the Missisiippi-Missouri freshwater fishes biota. Overall the results represent a first step toward the understanding of general hydrologic controls on complex ecologic systems
Transport in the hydrologic response: Travel time distributions, soil moisture dynamics, and the old water paradox
Full text linkWe propose a mathematical framework for the general definition and computation of
travel time distributions defined by the closure of a catchment control volume, where the
input flux is an arbitrary rainfall pattern and the output fluxes are green and blue water
flows (namely, evapotranspiration and the hydrologic response embedding runoff
production through soil water dynamics). The relevance of the problem is both practical,
owing to implications in hydrologic watershed modeling, and conceptual for the linkages
and the explanations the theory provides, chiefly concerning the role of geomorphology,
climate, soils, and vegetation through soil water dynamics and the treatment of the socalled
old water paradox. The work focuses in particular on the origins of the conditional
and time‐variant nature of travel time distributions and on the differences between unit
hydrographs and travel time distributions. Both carrier flow and solute matter transport in
the control volume are accounted for coherently. The key effect of mixing processes
occurring within runoff production is also investigated, in particular by a model that
assumes that mobilization of soil water involves randomly sampled particles from the
available storage. Travel time distributions are analytically expressed in terms of the major
water fluxes driving soil moisture dynamics, irrespectively of the specific model used to
compute them. Relevant numerical examples and a set of generalized applications are
provided and discussed
Nonpoint source transport models from empiricism to coherent theoretical frameworks
No full textBasin-scale transport of reactive solute species is studied through a class of stochastic models, termed mass response functions, which incorporate simplified concepts of chemical, physical or biological nonequilibrium kinetics into the theory of the hydrologic response. Here we examine the development of the field since its inception dealing with empirical approaches, a subject to which Giuseppe Bendoricchio actively contributed, and conclude that a coherent theoretical framework nowexists that allows to address large-scale transport problems for catchment studies where geomorphological and hydrological complexity is not simply ignored
Probing light dark scalars with future experiments
Full text linkWe investigate a dark sector containing a pair of light non-degenerate scalar
particles, with masses in the MeV-GeV range, coupled to the visible sector
through heavier mediators. The heaviest dark state is long-lived, and its
decays offer new testable signals. We analyze the prospects for detection with
the proposed beam-dump facility SHiP, and the proposed LHC experiments FASER
and MATHUSLA. Moreover, we consider bounds from the beam-dump experiment CHARM
and from colliders (LEP, LHC and BaBar). We present our results both in terms
of an effective field theory, where the heavy mediators have been integrated
out, and of a simplified model containing a vector boson mediator, which can be
heavy TeV, or light GeV. We show that
future experiments can test large portions of the parameter space currently
unexplored, and that they are complementary to future High-Luminosity LHC
searches.Comment: 25 pages, 2 appendices, 6 figures. v2: version accepted for
publication. Several clarifications added, Figs. 3-5 modified to take into
account the heaviest state decay length. Conclusions unchange
The see-saw portal at future Higgs factories: the role of dimension six operators
Full text linkWe study an extension of the Standard Model with electroweak scale
right-handed singlet fermions that induces neutrino masses, plus a generic
new physics sector at a higher scale . The latter is parametrized in
terms of effective operators in the language of the SMEFT. We study its
phenomenology considering operators up to , where additional production
and decay modes for are present in addition to those arising from the
mixing with the active neutrinos. We focus on the production with four-Fermi
operators and we identify the most relevant additional decay modes to be and . We assess the sensitivity of future Higgs factories
on the SMEFT in regions of the parameter space where the new states decay
promptly, displaced or are stable on detector lengths. We show that new physics
scale up to TeV can be explored, depending on the collider considered.Comment: 30 pages, 8 figures. v2: section with theoretical bounds added,
matches version accepted for publication in JHE
On the Lagrangian formulations of reactive solute transport in the hydrologic response
No full textWe address Lagrangian dispersion of reactive solutes in the framework of the formulation of transport by travel time distributions, specifically aiming at models of basin-scale, nonpoint transport applicable to complex geomorphological settings. We revisit existing exact solutions of the reactive transport problem derived in the convective stochastic framework and extend them to the case of transport of mass arbitrarily distributed (in time and space) within the immobile phase, a situation which is arguably suited to better describe nonpoint source solute transport driven by the hydrologic response. The initial conditions and, particularly, the mass initially stored in immobile rather than mobile phases bear a pronounced effect on the spatial and temporal moments of the solute plume. We also show that in many nonpoint source cases of interest (typically when heterogeneous conditions prevail) a simpler model of reaction kinetics, where spatial gradients in the immobile concentration are neglected, does well. Such a class of models, termed mass response functions, is known from the literature and has the property, beside being simplified in the mass exchange terms, of embedding unsteady flow forcing of the type typically employed in the theory of the hydrologic response. Thus, in the range of cases where the well-mixed assumption proves meaningful, we suggest a natural extension of current geomorphological models of the hydrologic response to generic transport phenomena
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