56 research outputs found
Environmental Costs of Government-Sponsored Agrarian Settlements in Brazilian Amazonia
Brazil has presided over the most comprehensive agrarian reform frontier colonization program on Earth, in which ~1.2 million settlers have been translocated by successive governments since the 1970's, mostly into forested hinterlands of Brazilian Amazonia. These settlements encompass 5.3% of this ~5 million km2 region, but have contributed with 13.5% of all land conversion into agropastoral land uses. The Brazilian Federal Agrarian Agency (INCRA) has repeatedly claimed that deforestation in these areas largely predates the sanctioned arrival of new settlers. Here, we quantify rates of natural vegetation conversion across 1911 agrarian settlements allocated to 568 Amazonian counties and compare fire incidence and deforestation rates before and after the official occupation of settlements by migrant farmers. The timing and spatial distribution of deforestation and fires in our analysis provides irrefutable chronological and spatially explicit evidence of agropastoral conversion both inside and immediately outside agrarian settlements over the last decade. Deforestation rates are strongly related to local human population density and road access to regional markets. Agrarian settlements consistently accelerated rates of deforestation and fires, compared to neighboring areas outside settlements, but within the same counties. Relocated smallholders allocated to forest areas undoubtedly operate as pivotal agents of deforestation, and most of the forest clearance occurs in the aftermath of government-induced migration
On hypercharge flux and exotics in F-theory GUTs
We study SU(5) Grand Unified Theories within a local framework in F-theory
with multiple extra U(1) symmetries arising from a small monodromy group. The
use of hypercharge flux for doublet-triplet splitting implies massless exotics
in the spectrum that are protected from obtaining a mass by the U(1)
symmetries. We find that lifting the exotics by giving vacuum expectation
values to some GUT singlets spontaneously breaks all the U(1) symmetries which
implies that proton decay operators are induced. If we impose an additional
R-parity symmetry by hand we find all the exotics can be lifted while proton
decay operators are still forbidden. These models can retain the gauge coupling
unification accuracy of the MSSM at 1-loop. For models where the generations
are distributed across multiple curves we also present a motivation for the
quark-lepton mass splittings at the GUT scale based on a Froggatt-Nielsen
approach to flavour.Comment: 38 pages; v2: emphasised possibility of avoiding exotics in models
without a global E8 structure, added ref, journal versio
Dilaton dominance relaxes LHC and cosmological constraints in supersymmetric models
It has been pointed out recently that the presence of dilaton field in the
early Universe can dilute the neutralino dark matter (DM) abundance, if
Universe is not radiation dominated at DM decoupling, due to its
dissipative-like coupling to DM. In this scenario two basic mechanisms compete,
the modified Hubble expansion rate tending to increase the relic density and a
dissipative force that tends to decrease it. The net effect can lead to an
overall dramatic decrease of the predicted relic abundance, sometimes by
amounts of the order of O(10^2) or so. This feature is rather generic,
independent of any particular assumption on the underlying string dynamics,
provided dilaton dominates at early eras after the end of inflation but before
Big Bang Nucleosynthesis (BBN). The latter ensures that BBN is not upset by the
presence of the dilaton. In this paper, within the context of such a scenario,
we study the phenomenology of the constrained minimal supersymmetric model
(CMSSM) by taking into account all recent experimental constraints, including
those from the LHC searches. We find that the allowed parameter space is
greatly enlarged and includes regions that are beyond the reach of LHC. The
allowed regions are compatible with Direct Dark Matter searches since the small
neutralino annihilation rates, that are now in accord with the cosmological
data on the relic density, imply small neutralino-nucleon cross sections below
the sensitivities of the Direct Dark Matter experiments. It is also important
that the new cosmologically accepted regions are compatible with Higgs boson
masses larger than 120 GeV, as it is indicated from the LHC experimental data.
The smaller annihilation cross sections needed to explain WMAP data require
that the detector performances of current and planned indirect DM search
experiments through gamma rays should be greatly improved in order to probe the
CMSSM regions.Comment: 20 pages, 10 eps figures. Revised and extended version to appear in
JHEP; a section on gamma rays adde
Climate change patterns in Amazonia and biodiversity
Precise characterization of hydroclimate variability in Amazonia on various timescales is critical to understanding the link between climate change and biodiversity. Here we present absolute-dated speleothem oxygen isotope records that characterize hydroclimate variation in western and eastern Amazonia over the past 250 and 20 ka, respectively. Although our records demonstrate the coherent millennial-scale precipitation variability across tropical-subtropical South America, the orbital-scale precipitation variability between western and eastern Amazonia exhibits a quasi-dipole pattern. During the last glacial period, our records imply a modest increase in precipitation amount in western Amazonia but a significant drying in eastern Amazonia, suggesting that higher biodiversity in western Amazonia, contrary to 'Refugia Hypothesis', is maintained under relatively stable climatic conditions. In contrast, the glacial-interglacial climatic perturbations might have been instances of loss rather than gain in biodiversity in eastern Amazonia, where forests may have been more susceptible to fragmentation in response to larger swings in hydroclimate. © 2013 Macmillan Publishers Limited. All rights reserved
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